1 //===------- SemaTemplateInstantiate.cpp - C++ Template Instantiation ------===/
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //===----------------------------------------------------------------------===/
8 //
9 //  This file implements C++ template instantiation.
10 //
11 //===----------------------------------------------------------------------===/
12 
13 #include "clang/Sema/SemaInternal.h"
14 #include "TreeTransform.h"
15 #include "clang/AST/ASTConsumer.h"
16 #include "clang/AST/ASTContext.h"
17 #include "clang/AST/ASTLambda.h"
18 #include "clang/AST/DeclTemplate.h"
19 #include "clang/AST/Expr.h"
20 #include "clang/Basic/LangOptions.h"
21 #include "clang/Sema/DeclSpec.h"
22 #include "clang/Sema/Initialization.h"
23 #include "clang/Sema/Lookup.h"
24 #include "clang/Sema/Template.h"
25 #include "clang/Sema/TemplateDeduction.h"
26 
27 using namespace clang;
28 using namespace sema;
29 
30 //===----------------------------------------------------------------------===/
31 // Template Instantiation Support
32 //===----------------------------------------------------------------------===/
33 
34 /// \brief Retrieve the template argument list(s) that should be used to
35 /// instantiate the definition of the given declaration.
36 ///
37 /// \param D the declaration for which we are computing template instantiation
38 /// arguments.
39 ///
40 /// \param Innermost if non-NULL, the innermost template argument list.
41 ///
42 /// \param RelativeToPrimary true if we should get the template
43 /// arguments relative to the primary template, even when we're
44 /// dealing with a specialization. This is only relevant for function
45 /// template specializations.
46 ///
47 /// \param Pattern If non-NULL, indicates the pattern from which we will be
48 /// instantiating the definition of the given declaration, \p D. This is
49 /// used to determine the proper set of template instantiation arguments for
50 /// friend function template specializations.
51 MultiLevelTemplateArgumentList
52 Sema::getTemplateInstantiationArgs(NamedDecl *D,
53                                    const TemplateArgumentList *Innermost,
54                                    bool RelativeToPrimary,
55                                    const FunctionDecl *Pattern) {
56   // Accumulate the set of template argument lists in this structure.
57   MultiLevelTemplateArgumentList Result;
58 
59   if (Innermost)
60     Result.addOuterTemplateArguments(Innermost);
61 
62   DeclContext *Ctx = dyn_cast<DeclContext>(D);
63   if (!Ctx) {
64     Ctx = D->getDeclContext();
65 
66     // Add template arguments from a variable template instantiation.
67     if (VarTemplateSpecializationDecl *Spec =
68             dyn_cast<VarTemplateSpecializationDecl>(D)) {
69       // We're done when we hit an explicit specialization.
70       if (Spec->getSpecializationKind() == TSK_ExplicitSpecialization &&
71           !isa<VarTemplatePartialSpecializationDecl>(Spec))
72         return Result;
73 
74       Result.addOuterTemplateArguments(&Spec->getTemplateInstantiationArgs());
75 
76       // If this variable template specialization was instantiated from a
77       // specialized member that is a variable template, we're done.
78       assert(Spec->getSpecializedTemplate() && "No variable template?");
79       llvm::PointerUnion<VarTemplateDecl*,
80                          VarTemplatePartialSpecializationDecl*> Specialized
81                              = Spec->getSpecializedTemplateOrPartial();
82       if (VarTemplatePartialSpecializationDecl *Partial =
83               Specialized.dyn_cast<VarTemplatePartialSpecializationDecl *>()) {
84         if (Partial->isMemberSpecialization())
85           return Result;
86       } else {
87         VarTemplateDecl *Tmpl = Specialized.get<VarTemplateDecl *>();
88         if (Tmpl->isMemberSpecialization())
89           return Result;
90       }
91     }
92 
93     // If we have a template template parameter with translation unit context,
94     // then we're performing substitution into a default template argument of
95     // this template template parameter before we've constructed the template
96     // that will own this template template parameter. In this case, we
97     // use empty template parameter lists for all of the outer templates
98     // to avoid performing any substitutions.
99     if (Ctx->isTranslationUnit()) {
100       if (TemplateTemplateParmDecl *TTP
101                                       = dyn_cast<TemplateTemplateParmDecl>(D)) {
102         for (unsigned I = 0, N = TTP->getDepth() + 1; I != N; ++I)
103           Result.addOuterTemplateArguments(None);
104         return Result;
105       }
106     }
107   }
108 
109   while (!Ctx->isFileContext()) {
110     // Add template arguments from a class template instantiation.
111     if (ClassTemplateSpecializationDecl *Spec
112           = dyn_cast<ClassTemplateSpecializationDecl>(Ctx)) {
113       // We're done when we hit an explicit specialization.
114       if (Spec->getSpecializationKind() == TSK_ExplicitSpecialization &&
115           !isa<ClassTemplatePartialSpecializationDecl>(Spec))
116         break;
117 
118       Result.addOuterTemplateArguments(&Spec->getTemplateInstantiationArgs());
119 
120       // If this class template specialization was instantiated from a
121       // specialized member that is a class template, we're done.
122       assert(Spec->getSpecializedTemplate() && "No class template?");
123       if (Spec->getSpecializedTemplate()->isMemberSpecialization())
124         break;
125     }
126     // Add template arguments from a function template specialization.
127     else if (FunctionDecl *Function = dyn_cast<FunctionDecl>(Ctx)) {
128       if (!RelativeToPrimary &&
129           (Function->getTemplateSpecializationKind() ==
130                                                   TSK_ExplicitSpecialization &&
131            !Function->getClassScopeSpecializationPattern()))
132         break;
133 
134       if (const TemplateArgumentList *TemplateArgs
135             = Function->getTemplateSpecializationArgs()) {
136         // Add the template arguments for this specialization.
137         Result.addOuterTemplateArguments(TemplateArgs);
138 
139         // If this function was instantiated from a specialized member that is
140         // a function template, we're done.
141         assert(Function->getPrimaryTemplate() && "No function template?");
142         if (Function->getPrimaryTemplate()->isMemberSpecialization())
143           break;
144 
145         // If this function is a generic lambda specialization, we are done.
146         if (isGenericLambdaCallOperatorSpecialization(Function))
147           break;
148 
149       } else if (FunctionTemplateDecl *FunTmpl
150                                    = Function->getDescribedFunctionTemplate()) {
151         // Add the "injected" template arguments.
152         Result.addOuterTemplateArguments(FunTmpl->getInjectedTemplateArgs());
153       }
154 
155       // If this is a friend declaration and it declares an entity at
156       // namespace scope, take arguments from its lexical parent
157       // instead of its semantic parent, unless of course the pattern we're
158       // instantiating actually comes from the file's context!
159       if (Function->getFriendObjectKind() &&
160           Function->getDeclContext()->isFileContext() &&
161           (!Pattern || !Pattern->getLexicalDeclContext()->isFileContext())) {
162         Ctx = Function->getLexicalDeclContext();
163         RelativeToPrimary = false;
164         continue;
165       }
166     } else if (CXXRecordDecl *Rec = dyn_cast<CXXRecordDecl>(Ctx)) {
167       if (ClassTemplateDecl *ClassTemplate = Rec->getDescribedClassTemplate()) {
168         QualType T = ClassTemplate->getInjectedClassNameSpecialization();
169         const TemplateSpecializationType *TST =
170             cast<TemplateSpecializationType>(Context.getCanonicalType(T));
171         Result.addOuterTemplateArguments(
172             llvm::makeArrayRef(TST->getArgs(), TST->getNumArgs()));
173         if (ClassTemplate->isMemberSpecialization())
174           break;
175       }
176     }
177 
178     Ctx = Ctx->getParent();
179     RelativeToPrimary = false;
180   }
181 
182   return Result;
183 }
184 
185 bool Sema::ActiveTemplateInstantiation::isInstantiationRecord() const {
186   switch (Kind) {
187   case TemplateInstantiation:
188   case ExceptionSpecInstantiation:
189   case DefaultTemplateArgumentInstantiation:
190   case DefaultFunctionArgumentInstantiation:
191   case ExplicitTemplateArgumentSubstitution:
192   case DeducedTemplateArgumentSubstitution:
193   case PriorTemplateArgumentSubstitution:
194     return true;
195 
196   case DefaultTemplateArgumentChecking:
197     return false;
198   }
199 
200   llvm_unreachable("Invalid InstantiationKind!");
201 }
202 
203 Sema::InstantiatingTemplate::InstantiatingTemplate(
204     Sema &SemaRef, ActiveTemplateInstantiation::InstantiationKind Kind,
205     SourceLocation PointOfInstantiation, SourceRange InstantiationRange,
206     Decl *Entity, NamedDecl *Template, ArrayRef<TemplateArgument> TemplateArgs,
207     sema::TemplateDeductionInfo *DeductionInfo)
208     : SemaRef(SemaRef), SavedInNonInstantiationSFINAEContext(
209                             SemaRef.InNonInstantiationSFINAEContext) {
210   // Don't allow further instantiation if a fatal error has occcured.  Any
211   // diagnostics we might have raised will not be visible.
212   if (SemaRef.Diags.hasFatalErrorOccurred()) {
213     Invalid = true;
214     return;
215   }
216   Invalid = CheckInstantiationDepth(PointOfInstantiation, InstantiationRange);
217   if (!Invalid) {
218     ActiveTemplateInstantiation Inst;
219     Inst.Kind = Kind;
220     Inst.PointOfInstantiation = PointOfInstantiation;
221     Inst.Entity = Entity;
222     Inst.Template = Template;
223     Inst.TemplateArgs = TemplateArgs.data();
224     Inst.NumTemplateArgs = TemplateArgs.size();
225     Inst.DeductionInfo = DeductionInfo;
226     Inst.InstantiationRange = InstantiationRange;
227     SemaRef.InNonInstantiationSFINAEContext = false;
228     SemaRef.ActiveTemplateInstantiations.push_back(Inst);
229     if (!Inst.isInstantiationRecord())
230       ++SemaRef.NonInstantiationEntries;
231   }
232 }
233 
234 Sema::InstantiatingTemplate::InstantiatingTemplate(
235     Sema &SemaRef, SourceLocation PointOfInstantiation, Decl *Entity,
236     SourceRange InstantiationRange)
237     : InstantiatingTemplate(SemaRef,
238                             ActiveTemplateInstantiation::TemplateInstantiation,
239                             PointOfInstantiation, InstantiationRange, Entity) {}
240 
241 Sema::InstantiatingTemplate::InstantiatingTemplate(
242     Sema &SemaRef, SourceLocation PointOfInstantiation, FunctionDecl *Entity,
243     ExceptionSpecification, SourceRange InstantiationRange)
244     : InstantiatingTemplate(
245           SemaRef, ActiveTemplateInstantiation::ExceptionSpecInstantiation,
246           PointOfInstantiation, InstantiationRange, Entity) {}
247 
248 Sema::InstantiatingTemplate::InstantiatingTemplate(
249     Sema &SemaRef, SourceLocation PointOfInstantiation, TemplateDecl *Template,
250     ArrayRef<TemplateArgument> TemplateArgs, SourceRange InstantiationRange)
251     : InstantiatingTemplate(
252           SemaRef,
253           ActiveTemplateInstantiation::DefaultTemplateArgumentInstantiation,
254           PointOfInstantiation, InstantiationRange, Template, nullptr,
255           TemplateArgs) {}
256 
257 Sema::InstantiatingTemplate::InstantiatingTemplate(
258     Sema &SemaRef, SourceLocation PointOfInstantiation,
259     FunctionTemplateDecl *FunctionTemplate,
260     ArrayRef<TemplateArgument> TemplateArgs,
261     ActiveTemplateInstantiation::InstantiationKind Kind,
262     sema::TemplateDeductionInfo &DeductionInfo, SourceRange InstantiationRange)
263     : InstantiatingTemplate(SemaRef, Kind, PointOfInstantiation,
264                             InstantiationRange, FunctionTemplate, nullptr,
265                             TemplateArgs, &DeductionInfo) {}
266 
267 Sema::InstantiatingTemplate::InstantiatingTemplate(
268     Sema &SemaRef, SourceLocation PointOfInstantiation,
269     ClassTemplatePartialSpecializationDecl *PartialSpec,
270     ArrayRef<TemplateArgument> TemplateArgs,
271     sema::TemplateDeductionInfo &DeductionInfo, SourceRange InstantiationRange)
272     : InstantiatingTemplate(
273           SemaRef,
274           ActiveTemplateInstantiation::DeducedTemplateArgumentSubstitution,
275           PointOfInstantiation, InstantiationRange, PartialSpec, nullptr,
276           TemplateArgs, &DeductionInfo) {}
277 
278 Sema::InstantiatingTemplate::InstantiatingTemplate(
279     Sema &SemaRef, SourceLocation PointOfInstantiation,
280     VarTemplatePartialSpecializationDecl *PartialSpec,
281     ArrayRef<TemplateArgument> TemplateArgs,
282     sema::TemplateDeductionInfo &DeductionInfo, SourceRange InstantiationRange)
283     : InstantiatingTemplate(
284           SemaRef,
285           ActiveTemplateInstantiation::DeducedTemplateArgumentSubstitution,
286           PointOfInstantiation, InstantiationRange, PartialSpec, nullptr,
287           TemplateArgs, &DeductionInfo) {}
288 
289 Sema::InstantiatingTemplate::InstantiatingTemplate(
290     Sema &SemaRef, SourceLocation PointOfInstantiation, ParmVarDecl *Param,
291     ArrayRef<TemplateArgument> TemplateArgs, SourceRange InstantiationRange)
292     : InstantiatingTemplate(
293           SemaRef,
294           ActiveTemplateInstantiation::DefaultFunctionArgumentInstantiation,
295           PointOfInstantiation, InstantiationRange, Param, nullptr,
296           TemplateArgs) {}
297 
298 Sema::InstantiatingTemplate::InstantiatingTemplate(
299     Sema &SemaRef, SourceLocation PointOfInstantiation, NamedDecl *Template,
300     NonTypeTemplateParmDecl *Param, ArrayRef<TemplateArgument> TemplateArgs,
301     SourceRange InstantiationRange)
302     : InstantiatingTemplate(
303           SemaRef,
304           ActiveTemplateInstantiation::PriorTemplateArgumentSubstitution,
305           PointOfInstantiation, InstantiationRange, Param, Template,
306           TemplateArgs) {}
307 
308 Sema::InstantiatingTemplate::InstantiatingTemplate(
309     Sema &SemaRef, SourceLocation PointOfInstantiation, NamedDecl *Template,
310     TemplateTemplateParmDecl *Param, ArrayRef<TemplateArgument> TemplateArgs,
311     SourceRange InstantiationRange)
312     : InstantiatingTemplate(
313           SemaRef,
314           ActiveTemplateInstantiation::PriorTemplateArgumentSubstitution,
315           PointOfInstantiation, InstantiationRange, Param, Template,
316           TemplateArgs) {}
317 
318 Sema::InstantiatingTemplate::InstantiatingTemplate(
319     Sema &SemaRef, SourceLocation PointOfInstantiation, TemplateDecl *Template,
320     NamedDecl *Param, ArrayRef<TemplateArgument> TemplateArgs,
321     SourceRange InstantiationRange)
322     : InstantiatingTemplate(
323           SemaRef, ActiveTemplateInstantiation::DefaultTemplateArgumentChecking,
324           PointOfInstantiation, InstantiationRange, Param, Template,
325           TemplateArgs) {}
326 
327 void Sema::InstantiatingTemplate::Clear() {
328   if (!Invalid) {
329     if (!SemaRef.ActiveTemplateInstantiations.back().isInstantiationRecord()) {
330       assert(SemaRef.NonInstantiationEntries > 0);
331       --SemaRef.NonInstantiationEntries;
332     }
333     SemaRef.InNonInstantiationSFINAEContext
334       = SavedInNonInstantiationSFINAEContext;
335 
336     // Name lookup no longer looks in this template's defining module.
337     assert(SemaRef.ActiveTemplateInstantiations.size() >=
338            SemaRef.ActiveTemplateInstantiationLookupModules.size() &&
339            "forgot to remove a lookup module for a template instantiation");
340     if (SemaRef.ActiveTemplateInstantiations.size() ==
341         SemaRef.ActiveTemplateInstantiationLookupModules.size()) {
342       if (Module *M = SemaRef.ActiveTemplateInstantiationLookupModules.back())
343         SemaRef.LookupModulesCache.erase(M);
344       SemaRef.ActiveTemplateInstantiationLookupModules.pop_back();
345     }
346 
347     SemaRef.ActiveTemplateInstantiations.pop_back();
348     Invalid = true;
349   }
350 }
351 
352 bool Sema::InstantiatingTemplate::CheckInstantiationDepth(
353                                         SourceLocation PointOfInstantiation,
354                                            SourceRange InstantiationRange) {
355   assert(SemaRef.NonInstantiationEntries <=
356                                    SemaRef.ActiveTemplateInstantiations.size());
357   if ((SemaRef.ActiveTemplateInstantiations.size() -
358           SemaRef.NonInstantiationEntries)
359         <= SemaRef.getLangOpts().InstantiationDepth)
360     return false;
361 
362   SemaRef.Diag(PointOfInstantiation,
363                diag::err_template_recursion_depth_exceeded)
364     << SemaRef.getLangOpts().InstantiationDepth
365     << InstantiationRange;
366   SemaRef.Diag(PointOfInstantiation, diag::note_template_recursion_depth)
367     << SemaRef.getLangOpts().InstantiationDepth;
368   return true;
369 }
370 
371 /// \brief Prints the current instantiation stack through a series of
372 /// notes.
373 void Sema::PrintInstantiationStack() {
374   // Determine which template instantiations to skip, if any.
375   unsigned SkipStart = ActiveTemplateInstantiations.size(), SkipEnd = SkipStart;
376   unsigned Limit = Diags.getTemplateBacktraceLimit();
377   if (Limit && Limit < ActiveTemplateInstantiations.size()) {
378     SkipStart = Limit / 2 + Limit % 2;
379     SkipEnd = ActiveTemplateInstantiations.size() - Limit / 2;
380   }
381 
382   // FIXME: In all of these cases, we need to show the template arguments
383   unsigned InstantiationIdx = 0;
384   for (SmallVectorImpl<ActiveTemplateInstantiation>::reverse_iterator
385          Active = ActiveTemplateInstantiations.rbegin(),
386          ActiveEnd = ActiveTemplateInstantiations.rend();
387        Active != ActiveEnd;
388        ++Active, ++InstantiationIdx) {
389     // Skip this instantiation?
390     if (InstantiationIdx >= SkipStart && InstantiationIdx < SkipEnd) {
391       if (InstantiationIdx == SkipStart) {
392         // Note that we're skipping instantiations.
393         Diags.Report(Active->PointOfInstantiation,
394                      diag::note_instantiation_contexts_suppressed)
395           << unsigned(ActiveTemplateInstantiations.size() - Limit);
396       }
397       continue;
398     }
399 
400     switch (Active->Kind) {
401     case ActiveTemplateInstantiation::TemplateInstantiation: {
402       Decl *D = Active->Entity;
403       if (CXXRecordDecl *Record = dyn_cast<CXXRecordDecl>(D)) {
404         unsigned DiagID = diag::note_template_member_class_here;
405         if (isa<ClassTemplateSpecializationDecl>(Record))
406           DiagID = diag::note_template_class_instantiation_here;
407         Diags.Report(Active->PointOfInstantiation, DiagID)
408           << Context.getTypeDeclType(Record)
409           << Active->InstantiationRange;
410       } else if (FunctionDecl *Function = dyn_cast<FunctionDecl>(D)) {
411         unsigned DiagID;
412         if (Function->getPrimaryTemplate())
413           DiagID = diag::note_function_template_spec_here;
414         else
415           DiagID = diag::note_template_member_function_here;
416         Diags.Report(Active->PointOfInstantiation, DiagID)
417           << Function
418           << Active->InstantiationRange;
419       } else if (VarDecl *VD = dyn_cast<VarDecl>(D)) {
420         Diags.Report(Active->PointOfInstantiation,
421                      VD->isStaticDataMember()?
422                        diag::note_template_static_data_member_def_here
423                      : diag::note_template_variable_def_here)
424           << VD
425           << Active->InstantiationRange;
426       } else if (EnumDecl *ED = dyn_cast<EnumDecl>(D)) {
427         Diags.Report(Active->PointOfInstantiation,
428                      diag::note_template_enum_def_here)
429           << ED
430           << Active->InstantiationRange;
431       } else if (FieldDecl *FD = dyn_cast<FieldDecl>(D)) {
432         Diags.Report(Active->PointOfInstantiation,
433                      diag::note_template_nsdmi_here)
434             << FD << Active->InstantiationRange;
435       } else {
436         Diags.Report(Active->PointOfInstantiation,
437                      diag::note_template_type_alias_instantiation_here)
438           << cast<TypeAliasTemplateDecl>(D)
439           << Active->InstantiationRange;
440       }
441       break;
442     }
443 
444     case ActiveTemplateInstantiation::DefaultTemplateArgumentInstantiation: {
445       TemplateDecl *Template = cast<TemplateDecl>(Active->Entity);
446       SmallVector<char, 128> TemplateArgsStr;
447       llvm::raw_svector_ostream OS(TemplateArgsStr);
448       Template->printName(OS);
449       TemplateSpecializationType::PrintTemplateArgumentList(OS,
450                                                          Active->TemplateArgs,
451                                                       Active->NumTemplateArgs,
452                                                       getPrintingPolicy());
453       Diags.Report(Active->PointOfInstantiation,
454                    diag::note_default_arg_instantiation_here)
455         << OS.str()
456         << Active->InstantiationRange;
457       break;
458     }
459 
460     case ActiveTemplateInstantiation::ExplicitTemplateArgumentSubstitution: {
461       FunctionTemplateDecl *FnTmpl = cast<FunctionTemplateDecl>(Active->Entity);
462       Diags.Report(Active->PointOfInstantiation,
463                    diag::note_explicit_template_arg_substitution_here)
464         << FnTmpl
465         << getTemplateArgumentBindingsText(FnTmpl->getTemplateParameters(),
466                                            Active->TemplateArgs,
467                                            Active->NumTemplateArgs)
468         << Active->InstantiationRange;
469       break;
470     }
471 
472     case ActiveTemplateInstantiation::DeducedTemplateArgumentSubstitution:
473       if (ClassTemplatePartialSpecializationDecl *PartialSpec =
474             dyn_cast<ClassTemplatePartialSpecializationDecl>(Active->Entity)) {
475         Diags.Report(Active->PointOfInstantiation,
476                      diag::note_partial_spec_deduct_instantiation_here)
477           << Context.getTypeDeclType(PartialSpec)
478           << getTemplateArgumentBindingsText(
479                                          PartialSpec->getTemplateParameters(),
480                                              Active->TemplateArgs,
481                                              Active->NumTemplateArgs)
482           << Active->InstantiationRange;
483       } else {
484         FunctionTemplateDecl *FnTmpl
485           = cast<FunctionTemplateDecl>(Active->Entity);
486         Diags.Report(Active->PointOfInstantiation,
487                      diag::note_function_template_deduction_instantiation_here)
488           << FnTmpl
489           << getTemplateArgumentBindingsText(FnTmpl->getTemplateParameters(),
490                                              Active->TemplateArgs,
491                                              Active->NumTemplateArgs)
492           << Active->InstantiationRange;
493       }
494       break;
495 
496     case ActiveTemplateInstantiation::DefaultFunctionArgumentInstantiation: {
497       ParmVarDecl *Param = cast<ParmVarDecl>(Active->Entity);
498       FunctionDecl *FD = cast<FunctionDecl>(Param->getDeclContext());
499 
500       SmallVector<char, 128> TemplateArgsStr;
501       llvm::raw_svector_ostream OS(TemplateArgsStr);
502       FD->printName(OS);
503       TemplateSpecializationType::PrintTemplateArgumentList(OS,
504                                                          Active->TemplateArgs,
505                                                       Active->NumTemplateArgs,
506                                                       getPrintingPolicy());
507       Diags.Report(Active->PointOfInstantiation,
508                    diag::note_default_function_arg_instantiation_here)
509         << OS.str()
510         << Active->InstantiationRange;
511       break;
512     }
513 
514     case ActiveTemplateInstantiation::PriorTemplateArgumentSubstitution: {
515       NamedDecl *Parm = cast<NamedDecl>(Active->Entity);
516       std::string Name;
517       if (!Parm->getName().empty())
518         Name = std::string(" '") + Parm->getName().str() + "'";
519 
520       TemplateParameterList *TemplateParams = nullptr;
521       if (TemplateDecl *Template = dyn_cast<TemplateDecl>(Active->Template))
522         TemplateParams = Template->getTemplateParameters();
523       else
524         TemplateParams =
525           cast<ClassTemplatePartialSpecializationDecl>(Active->Template)
526                                                       ->getTemplateParameters();
527       Diags.Report(Active->PointOfInstantiation,
528                    diag::note_prior_template_arg_substitution)
529         << isa<TemplateTemplateParmDecl>(Parm)
530         << Name
531         << getTemplateArgumentBindingsText(TemplateParams,
532                                            Active->TemplateArgs,
533                                            Active->NumTemplateArgs)
534         << Active->InstantiationRange;
535       break;
536     }
537 
538     case ActiveTemplateInstantiation::DefaultTemplateArgumentChecking: {
539       TemplateParameterList *TemplateParams = nullptr;
540       if (TemplateDecl *Template = dyn_cast<TemplateDecl>(Active->Template))
541         TemplateParams = Template->getTemplateParameters();
542       else
543         TemplateParams =
544           cast<ClassTemplatePartialSpecializationDecl>(Active->Template)
545                                                       ->getTemplateParameters();
546 
547       Diags.Report(Active->PointOfInstantiation,
548                    diag::note_template_default_arg_checking)
549         << getTemplateArgumentBindingsText(TemplateParams,
550                                            Active->TemplateArgs,
551                                            Active->NumTemplateArgs)
552         << Active->InstantiationRange;
553       break;
554     }
555 
556     case ActiveTemplateInstantiation::ExceptionSpecInstantiation:
557       Diags.Report(Active->PointOfInstantiation,
558                    diag::note_template_exception_spec_instantiation_here)
559         << cast<FunctionDecl>(Active->Entity)
560         << Active->InstantiationRange;
561       break;
562     }
563   }
564 }
565 
566 Optional<TemplateDeductionInfo *> Sema::isSFINAEContext() const {
567   if (InNonInstantiationSFINAEContext)
568     return Optional<TemplateDeductionInfo *>(nullptr);
569 
570   for (SmallVectorImpl<ActiveTemplateInstantiation>::const_reverse_iterator
571          Active = ActiveTemplateInstantiations.rbegin(),
572          ActiveEnd = ActiveTemplateInstantiations.rend();
573        Active != ActiveEnd;
574        ++Active)
575   {
576     switch(Active->Kind) {
577     case ActiveTemplateInstantiation::TemplateInstantiation:
578       // An instantiation of an alias template may or may not be a SFINAE
579       // context, depending on what else is on the stack.
580       if (isa<TypeAliasTemplateDecl>(Active->Entity))
581         break;
582       // Fall through.
583     case ActiveTemplateInstantiation::DefaultFunctionArgumentInstantiation:
584     case ActiveTemplateInstantiation::ExceptionSpecInstantiation:
585       // This is a template instantiation, so there is no SFINAE.
586       return None;
587 
588     case ActiveTemplateInstantiation::DefaultTemplateArgumentInstantiation:
589     case ActiveTemplateInstantiation::PriorTemplateArgumentSubstitution:
590     case ActiveTemplateInstantiation::DefaultTemplateArgumentChecking:
591       // A default template argument instantiation and substitution into
592       // template parameters with arguments for prior parameters may or may
593       // not be a SFINAE context; look further up the stack.
594       break;
595 
596     case ActiveTemplateInstantiation::ExplicitTemplateArgumentSubstitution:
597     case ActiveTemplateInstantiation::DeducedTemplateArgumentSubstitution:
598       // We're either substitution explicitly-specified template arguments
599       // or deduced template arguments, so SFINAE applies.
600       assert(Active->DeductionInfo && "Missing deduction info pointer");
601       return Active->DeductionInfo;
602     }
603   }
604 
605   return None;
606 }
607 
608 /// \brief Retrieve the depth and index of a parameter pack.
609 static std::pair<unsigned, unsigned>
610 getDepthAndIndex(NamedDecl *ND) {
611   if (TemplateTypeParmDecl *TTP = dyn_cast<TemplateTypeParmDecl>(ND))
612     return std::make_pair(TTP->getDepth(), TTP->getIndex());
613 
614   if (NonTypeTemplateParmDecl *NTTP = dyn_cast<NonTypeTemplateParmDecl>(ND))
615     return std::make_pair(NTTP->getDepth(), NTTP->getIndex());
616 
617   TemplateTemplateParmDecl *TTP = cast<TemplateTemplateParmDecl>(ND);
618   return std::make_pair(TTP->getDepth(), TTP->getIndex());
619 }
620 
621 //===----------------------------------------------------------------------===/
622 // Template Instantiation for Types
623 //===----------------------------------------------------------------------===/
624 namespace {
625   class TemplateInstantiator : public TreeTransform<TemplateInstantiator> {
626     const MultiLevelTemplateArgumentList &TemplateArgs;
627     SourceLocation Loc;
628     DeclarationName Entity;
629 
630   public:
631     typedef TreeTransform<TemplateInstantiator> inherited;
632 
633     TemplateInstantiator(Sema &SemaRef,
634                          const MultiLevelTemplateArgumentList &TemplateArgs,
635                          SourceLocation Loc,
636                          DeclarationName Entity)
637       : inherited(SemaRef), TemplateArgs(TemplateArgs), Loc(Loc),
638         Entity(Entity) { }
639 
640     /// \brief Determine whether the given type \p T has already been
641     /// transformed.
642     ///
643     /// For the purposes of template instantiation, a type has already been
644     /// transformed if it is NULL or if it is not dependent.
645     bool AlreadyTransformed(QualType T);
646 
647     /// \brief Returns the location of the entity being instantiated, if known.
648     SourceLocation getBaseLocation() { return Loc; }
649 
650     /// \brief Returns the name of the entity being instantiated, if any.
651     DeclarationName getBaseEntity() { return Entity; }
652 
653     /// \brief Sets the "base" location and entity when that
654     /// information is known based on another transformation.
655     void setBase(SourceLocation Loc, DeclarationName Entity) {
656       this->Loc = Loc;
657       this->Entity = Entity;
658     }
659 
660     bool TryExpandParameterPacks(SourceLocation EllipsisLoc,
661                                  SourceRange PatternRange,
662                                  ArrayRef<UnexpandedParameterPack> Unexpanded,
663                                  bool &ShouldExpand, bool &RetainExpansion,
664                                  Optional<unsigned> &NumExpansions) {
665       return getSema().CheckParameterPacksForExpansion(EllipsisLoc,
666                                                        PatternRange, Unexpanded,
667                                                        TemplateArgs,
668                                                        ShouldExpand,
669                                                        RetainExpansion,
670                                                        NumExpansions);
671     }
672 
673     void ExpandingFunctionParameterPack(ParmVarDecl *Pack) {
674       SemaRef.CurrentInstantiationScope->MakeInstantiatedLocalArgPack(Pack);
675     }
676 
677     TemplateArgument ForgetPartiallySubstitutedPack() {
678       TemplateArgument Result;
679       if (NamedDecl *PartialPack
680             = SemaRef.CurrentInstantiationScope->getPartiallySubstitutedPack()){
681         MultiLevelTemplateArgumentList &TemplateArgs
682           = const_cast<MultiLevelTemplateArgumentList &>(this->TemplateArgs);
683         unsigned Depth, Index;
684         std::tie(Depth, Index) = getDepthAndIndex(PartialPack);
685         if (TemplateArgs.hasTemplateArgument(Depth, Index)) {
686           Result = TemplateArgs(Depth, Index);
687           TemplateArgs.setArgument(Depth, Index, TemplateArgument());
688         }
689       }
690 
691       return Result;
692     }
693 
694     void RememberPartiallySubstitutedPack(TemplateArgument Arg) {
695       if (Arg.isNull())
696         return;
697 
698       if (NamedDecl *PartialPack
699             = SemaRef.CurrentInstantiationScope->getPartiallySubstitutedPack()){
700         MultiLevelTemplateArgumentList &TemplateArgs
701         = const_cast<MultiLevelTemplateArgumentList &>(this->TemplateArgs);
702         unsigned Depth, Index;
703         std::tie(Depth, Index) = getDepthAndIndex(PartialPack);
704         TemplateArgs.setArgument(Depth, Index, Arg);
705       }
706     }
707 
708     /// \brief Transform the given declaration by instantiating a reference to
709     /// this declaration.
710     Decl *TransformDecl(SourceLocation Loc, Decl *D);
711 
712     void transformAttrs(Decl *Old, Decl *New) {
713       SemaRef.InstantiateAttrs(TemplateArgs, Old, New);
714     }
715 
716     void transformedLocalDecl(Decl *Old, Decl *New) {
717       // If we've instantiated the call operator of a lambda or the call
718       // operator template of a generic lambda, update the "instantiation of"
719       // information.
720       auto *NewMD = dyn_cast<CXXMethodDecl>(New);
721       if (NewMD && isLambdaCallOperator(NewMD)) {
722         auto *OldMD = dyn_cast<CXXMethodDecl>(Old);
723         if (auto *NewTD = NewMD->getDescribedFunctionTemplate())
724           NewTD->setInstantiatedFromMemberTemplate(
725               OldMD->getDescribedFunctionTemplate());
726         else
727           NewMD->setInstantiationOfMemberFunction(OldMD,
728                                                   TSK_ImplicitInstantiation);
729       }
730 
731       SemaRef.CurrentInstantiationScope->InstantiatedLocal(Old, New);
732     }
733 
734     /// \brief Transform the definition of the given declaration by
735     /// instantiating it.
736     Decl *TransformDefinition(SourceLocation Loc, Decl *D);
737 
738     /// \brief Transform the first qualifier within a scope by instantiating the
739     /// declaration.
740     NamedDecl *TransformFirstQualifierInScope(NamedDecl *D, SourceLocation Loc);
741 
742     /// \brief Rebuild the exception declaration and register the declaration
743     /// as an instantiated local.
744     VarDecl *RebuildExceptionDecl(VarDecl *ExceptionDecl,
745                                   TypeSourceInfo *Declarator,
746                                   SourceLocation StartLoc,
747                                   SourceLocation NameLoc,
748                                   IdentifierInfo *Name);
749 
750     /// \brief Rebuild the Objective-C exception declaration and register the
751     /// declaration as an instantiated local.
752     VarDecl *RebuildObjCExceptionDecl(VarDecl *ExceptionDecl,
753                                       TypeSourceInfo *TSInfo, QualType T);
754 
755     /// \brief Check for tag mismatches when instantiating an
756     /// elaborated type.
757     QualType RebuildElaboratedType(SourceLocation KeywordLoc,
758                                    ElaboratedTypeKeyword Keyword,
759                                    NestedNameSpecifierLoc QualifierLoc,
760                                    QualType T);
761 
762     TemplateName
763     TransformTemplateName(CXXScopeSpec &SS, TemplateName Name,
764                           SourceLocation NameLoc,
765                           QualType ObjectType = QualType(),
766                           NamedDecl *FirstQualifierInScope = nullptr);
767 
768     const LoopHintAttr *TransformLoopHintAttr(const LoopHintAttr *LH);
769 
770     ExprResult TransformPredefinedExpr(PredefinedExpr *E);
771     ExprResult TransformDeclRefExpr(DeclRefExpr *E);
772     ExprResult TransformCXXDefaultArgExpr(CXXDefaultArgExpr *E);
773 
774     ExprResult TransformTemplateParmRefExpr(DeclRefExpr *E,
775                                             NonTypeTemplateParmDecl *D);
776     ExprResult TransformSubstNonTypeTemplateParmPackExpr(
777                                            SubstNonTypeTemplateParmPackExpr *E);
778 
779     /// \brief Rebuild a DeclRefExpr for a ParmVarDecl reference.
780     ExprResult RebuildParmVarDeclRefExpr(ParmVarDecl *PD, SourceLocation Loc);
781 
782     /// \brief Transform a reference to a function parameter pack.
783     ExprResult TransformFunctionParmPackRefExpr(DeclRefExpr *E,
784                                                 ParmVarDecl *PD);
785 
786     /// \brief Transform a FunctionParmPackExpr which was built when we couldn't
787     /// expand a function parameter pack reference which refers to an expanded
788     /// pack.
789     ExprResult TransformFunctionParmPackExpr(FunctionParmPackExpr *E);
790 
791     QualType TransformFunctionProtoType(TypeLocBuilder &TLB,
792                                         FunctionProtoTypeLoc TL) {
793       // Call the base version; it will forward to our overridden version below.
794       return inherited::TransformFunctionProtoType(TLB, TL);
795     }
796 
797     template<typename Fn>
798     QualType TransformFunctionProtoType(TypeLocBuilder &TLB,
799                                         FunctionProtoTypeLoc TL,
800                                         CXXRecordDecl *ThisContext,
801                                         unsigned ThisTypeQuals,
802                                         Fn TransformExceptionSpec);
803 
804     ParmVarDecl *TransformFunctionTypeParam(ParmVarDecl *OldParm,
805                                             int indexAdjustment,
806                                             Optional<unsigned> NumExpansions,
807                                             bool ExpectParameterPack);
808 
809     /// \brief Transforms a template type parameter type by performing
810     /// substitution of the corresponding template type argument.
811     QualType TransformTemplateTypeParmType(TypeLocBuilder &TLB,
812                                            TemplateTypeParmTypeLoc TL);
813 
814     /// \brief Transforms an already-substituted template type parameter pack
815     /// into either itself (if we aren't substituting into its pack expansion)
816     /// or the appropriate substituted argument.
817     QualType TransformSubstTemplateTypeParmPackType(TypeLocBuilder &TLB,
818                                            SubstTemplateTypeParmPackTypeLoc TL);
819 
820     ExprResult TransformLambdaExpr(LambdaExpr *E) {
821       LocalInstantiationScope Scope(SemaRef, /*CombineWithOuterScope=*/true);
822       return TreeTransform<TemplateInstantiator>::TransformLambdaExpr(E);
823     }
824 
825     TemplateParameterList *TransformTemplateParameterList(
826                               TemplateParameterList *OrigTPL)  {
827       if (!OrigTPL || !OrigTPL->size()) return OrigTPL;
828 
829       DeclContext *Owner = OrigTPL->getParam(0)->getDeclContext();
830       TemplateDeclInstantiator  DeclInstantiator(getSema(),
831                         /* DeclContext *Owner */ Owner, TemplateArgs);
832       return DeclInstantiator.SubstTemplateParams(OrigTPL);
833     }
834   private:
835     ExprResult transformNonTypeTemplateParmRef(NonTypeTemplateParmDecl *parm,
836                                                SourceLocation loc,
837                                                TemplateArgument arg);
838   };
839 }
840 
841 bool TemplateInstantiator::AlreadyTransformed(QualType T) {
842   if (T.isNull())
843     return true;
844 
845   if (T->isInstantiationDependentType() || T->isVariablyModifiedType())
846     return false;
847 
848   getSema().MarkDeclarationsReferencedInType(Loc, T);
849   return true;
850 }
851 
852 static TemplateArgument
853 getPackSubstitutedTemplateArgument(Sema &S, TemplateArgument Arg) {
854   assert(S.ArgumentPackSubstitutionIndex >= 0);
855   assert(S.ArgumentPackSubstitutionIndex < (int)Arg.pack_size());
856   Arg = Arg.pack_begin()[S.ArgumentPackSubstitutionIndex];
857   if (Arg.isPackExpansion())
858     Arg = Arg.getPackExpansionPattern();
859   return Arg;
860 }
861 
862 Decl *TemplateInstantiator::TransformDecl(SourceLocation Loc, Decl *D) {
863   if (!D)
864     return nullptr;
865 
866   if (TemplateTemplateParmDecl *TTP = dyn_cast<TemplateTemplateParmDecl>(D)) {
867     if (TTP->getDepth() < TemplateArgs.getNumLevels()) {
868       // If the corresponding template argument is NULL or non-existent, it's
869       // because we are performing instantiation from explicitly-specified
870       // template arguments in a function template, but there were some
871       // arguments left unspecified.
872       if (!TemplateArgs.hasTemplateArgument(TTP->getDepth(),
873                                             TTP->getPosition()))
874         return D;
875 
876       TemplateArgument Arg = TemplateArgs(TTP->getDepth(), TTP->getPosition());
877 
878       if (TTP->isParameterPack()) {
879         assert(Arg.getKind() == TemplateArgument::Pack &&
880                "Missing argument pack");
881         Arg = getPackSubstitutedTemplateArgument(getSema(), Arg);
882       }
883 
884       TemplateName Template = Arg.getAsTemplate();
885       assert(!Template.isNull() && Template.getAsTemplateDecl() &&
886              "Wrong kind of template template argument");
887       return Template.getAsTemplateDecl();
888     }
889 
890     // Fall through to find the instantiated declaration for this template
891     // template parameter.
892   }
893 
894   return SemaRef.FindInstantiatedDecl(Loc, cast<NamedDecl>(D), TemplateArgs);
895 }
896 
897 Decl *TemplateInstantiator::TransformDefinition(SourceLocation Loc, Decl *D) {
898   Decl *Inst = getSema().SubstDecl(D, getSema().CurContext, TemplateArgs);
899   if (!Inst)
900     return nullptr;
901 
902   getSema().CurrentInstantiationScope->InstantiatedLocal(D, Inst);
903   return Inst;
904 }
905 
906 NamedDecl *
907 TemplateInstantiator::TransformFirstQualifierInScope(NamedDecl *D,
908                                                      SourceLocation Loc) {
909   // If the first part of the nested-name-specifier was a template type
910   // parameter, instantiate that type parameter down to a tag type.
911   if (TemplateTypeParmDecl *TTPD = dyn_cast_or_null<TemplateTypeParmDecl>(D)) {
912     const TemplateTypeParmType *TTP
913       = cast<TemplateTypeParmType>(getSema().Context.getTypeDeclType(TTPD));
914 
915     if (TTP->getDepth() < TemplateArgs.getNumLevels()) {
916       // FIXME: This needs testing w/ member access expressions.
917       TemplateArgument Arg = TemplateArgs(TTP->getDepth(), TTP->getIndex());
918 
919       if (TTP->isParameterPack()) {
920         assert(Arg.getKind() == TemplateArgument::Pack &&
921                "Missing argument pack");
922 
923         if (getSema().ArgumentPackSubstitutionIndex == -1)
924           return nullptr;
925 
926         Arg = getPackSubstitutedTemplateArgument(getSema(), Arg);
927       }
928 
929       QualType T = Arg.getAsType();
930       if (T.isNull())
931         return cast_or_null<NamedDecl>(TransformDecl(Loc, D));
932 
933       if (const TagType *Tag = T->getAs<TagType>())
934         return Tag->getDecl();
935 
936       // The resulting type is not a tag; complain.
937       getSema().Diag(Loc, diag::err_nested_name_spec_non_tag) << T;
938       return nullptr;
939     }
940   }
941 
942   return cast_or_null<NamedDecl>(TransformDecl(Loc, D));
943 }
944 
945 VarDecl *
946 TemplateInstantiator::RebuildExceptionDecl(VarDecl *ExceptionDecl,
947                                            TypeSourceInfo *Declarator,
948                                            SourceLocation StartLoc,
949                                            SourceLocation NameLoc,
950                                            IdentifierInfo *Name) {
951   VarDecl *Var = inherited::RebuildExceptionDecl(ExceptionDecl, Declarator,
952                                                  StartLoc, NameLoc, Name);
953   if (Var)
954     getSema().CurrentInstantiationScope->InstantiatedLocal(ExceptionDecl, Var);
955   return Var;
956 }
957 
958 VarDecl *TemplateInstantiator::RebuildObjCExceptionDecl(VarDecl *ExceptionDecl,
959                                                         TypeSourceInfo *TSInfo,
960                                                         QualType T) {
961   VarDecl *Var = inherited::RebuildObjCExceptionDecl(ExceptionDecl, TSInfo, T);
962   if (Var)
963     getSema().CurrentInstantiationScope->InstantiatedLocal(ExceptionDecl, Var);
964   return Var;
965 }
966 
967 QualType
968 TemplateInstantiator::RebuildElaboratedType(SourceLocation KeywordLoc,
969                                             ElaboratedTypeKeyword Keyword,
970                                             NestedNameSpecifierLoc QualifierLoc,
971                                             QualType T) {
972   if (const TagType *TT = T->getAs<TagType>()) {
973     TagDecl* TD = TT->getDecl();
974 
975     SourceLocation TagLocation = KeywordLoc;
976 
977     IdentifierInfo *Id = TD->getIdentifier();
978 
979     // TODO: should we even warn on struct/class mismatches for this?  Seems
980     // like it's likely to produce a lot of spurious errors.
981     if (Id && Keyword != ETK_None && Keyword != ETK_Typename) {
982       TagTypeKind Kind = TypeWithKeyword::getTagTypeKindForKeyword(Keyword);
983       if (!SemaRef.isAcceptableTagRedeclaration(TD, Kind, /*isDefinition*/false,
984                                                 TagLocation, Id)) {
985         SemaRef.Diag(TagLocation, diag::err_use_with_wrong_tag)
986           << Id
987           << FixItHint::CreateReplacement(SourceRange(TagLocation),
988                                           TD->getKindName());
989         SemaRef.Diag(TD->getLocation(), diag::note_previous_use);
990       }
991     }
992   }
993 
994   return TreeTransform<TemplateInstantiator>::RebuildElaboratedType(KeywordLoc,
995                                                                     Keyword,
996                                                                   QualifierLoc,
997                                                                     T);
998 }
999 
1000 TemplateName TemplateInstantiator::TransformTemplateName(CXXScopeSpec &SS,
1001                                                          TemplateName Name,
1002                                                          SourceLocation NameLoc,
1003                                                          QualType ObjectType,
1004                                              NamedDecl *FirstQualifierInScope) {
1005   if (TemplateTemplateParmDecl *TTP
1006        = dyn_cast_or_null<TemplateTemplateParmDecl>(Name.getAsTemplateDecl())) {
1007     if (TTP->getDepth() < TemplateArgs.getNumLevels()) {
1008       // If the corresponding template argument is NULL or non-existent, it's
1009       // because we are performing instantiation from explicitly-specified
1010       // template arguments in a function template, but there were some
1011       // arguments left unspecified.
1012       if (!TemplateArgs.hasTemplateArgument(TTP->getDepth(),
1013                                             TTP->getPosition()))
1014         return Name;
1015 
1016       TemplateArgument Arg = TemplateArgs(TTP->getDepth(), TTP->getPosition());
1017 
1018       if (TTP->isParameterPack()) {
1019         assert(Arg.getKind() == TemplateArgument::Pack &&
1020                "Missing argument pack");
1021 
1022         if (getSema().ArgumentPackSubstitutionIndex == -1) {
1023           // We have the template argument pack to substitute, but we're not
1024           // actually expanding the enclosing pack expansion yet. So, just
1025           // keep the entire argument pack.
1026           return getSema().Context.getSubstTemplateTemplateParmPack(TTP, Arg);
1027         }
1028 
1029         Arg = getPackSubstitutedTemplateArgument(getSema(), Arg);
1030       }
1031 
1032       TemplateName Template = Arg.getAsTemplate();
1033       assert(!Template.isNull() && "Null template template argument");
1034 
1035       // We don't ever want to substitute for a qualified template name, since
1036       // the qualifier is handled separately. So, look through the qualified
1037       // template name to its underlying declaration.
1038       if (QualifiedTemplateName *QTN = Template.getAsQualifiedTemplateName())
1039         Template = TemplateName(QTN->getTemplateDecl());
1040 
1041       Template = getSema().Context.getSubstTemplateTemplateParm(TTP, Template);
1042       return Template;
1043     }
1044   }
1045 
1046   if (SubstTemplateTemplateParmPackStorage *SubstPack
1047       = Name.getAsSubstTemplateTemplateParmPack()) {
1048     if (getSema().ArgumentPackSubstitutionIndex == -1)
1049       return Name;
1050 
1051     TemplateArgument Arg = SubstPack->getArgumentPack();
1052     Arg = getPackSubstitutedTemplateArgument(getSema(), Arg);
1053     return Arg.getAsTemplate();
1054   }
1055 
1056   return inherited::TransformTemplateName(SS, Name, NameLoc, ObjectType,
1057                                           FirstQualifierInScope);
1058 }
1059 
1060 ExprResult
1061 TemplateInstantiator::TransformPredefinedExpr(PredefinedExpr *E) {
1062   if (!E->isTypeDependent())
1063     return E;
1064 
1065   return getSema().BuildPredefinedExpr(E->getLocation(), E->getIdentType());
1066 }
1067 
1068 ExprResult
1069 TemplateInstantiator::TransformTemplateParmRefExpr(DeclRefExpr *E,
1070                                                NonTypeTemplateParmDecl *NTTP) {
1071   // If the corresponding template argument is NULL or non-existent, it's
1072   // because we are performing instantiation from explicitly-specified
1073   // template arguments in a function template, but there were some
1074   // arguments left unspecified.
1075   if (!TemplateArgs.hasTemplateArgument(NTTP->getDepth(),
1076                                         NTTP->getPosition()))
1077     return E;
1078 
1079   TemplateArgument Arg = TemplateArgs(NTTP->getDepth(), NTTP->getPosition());
1080   if (NTTP->isParameterPack()) {
1081     assert(Arg.getKind() == TemplateArgument::Pack &&
1082            "Missing argument pack");
1083 
1084     if (getSema().ArgumentPackSubstitutionIndex == -1) {
1085       // We have an argument pack, but we can't select a particular argument
1086       // out of it yet. Therefore, we'll build an expression to hold on to that
1087       // argument pack.
1088       QualType TargetType = SemaRef.SubstType(NTTP->getType(), TemplateArgs,
1089                                               E->getLocation(),
1090                                               NTTP->getDeclName());
1091       if (TargetType.isNull())
1092         return ExprError();
1093 
1094       return new (SemaRef.Context) SubstNonTypeTemplateParmPackExpr(TargetType,
1095                                                                     NTTP,
1096                                                               E->getLocation(),
1097                                                                     Arg);
1098     }
1099 
1100     Arg = getPackSubstitutedTemplateArgument(getSema(), Arg);
1101   }
1102 
1103   return transformNonTypeTemplateParmRef(NTTP, E->getLocation(), Arg);
1104 }
1105 
1106 const LoopHintAttr *
1107 TemplateInstantiator::TransformLoopHintAttr(const LoopHintAttr *LH) {
1108   Expr *TransformedExpr = getDerived().TransformExpr(LH->getValue()).get();
1109 
1110   if (TransformedExpr == LH->getValue())
1111     return LH;
1112 
1113   // Generate error if there is a problem with the value.
1114   if (getSema().CheckLoopHintExpr(TransformedExpr, LH->getLocation()))
1115     return LH;
1116 
1117   // Create new LoopHintValueAttr with integral expression in place of the
1118   // non-type template parameter.
1119   return LoopHintAttr::CreateImplicit(
1120       getSema().Context, LH->getSemanticSpelling(), LH->getOption(),
1121       LH->getState(), TransformedExpr, LH->getRange());
1122 }
1123 
1124 ExprResult TemplateInstantiator::transformNonTypeTemplateParmRef(
1125                                                  NonTypeTemplateParmDecl *parm,
1126                                                  SourceLocation loc,
1127                                                  TemplateArgument arg) {
1128   ExprResult result;
1129   QualType type;
1130 
1131   // The template argument itself might be an expression, in which
1132   // case we just return that expression.
1133   if (arg.getKind() == TemplateArgument::Expression) {
1134     Expr *argExpr = arg.getAsExpr();
1135     result = argExpr;
1136     type = argExpr->getType();
1137 
1138   } else if (arg.getKind() == TemplateArgument::Declaration ||
1139              arg.getKind() == TemplateArgument::NullPtr) {
1140     ValueDecl *VD;
1141     if (arg.getKind() == TemplateArgument::Declaration) {
1142       VD = cast<ValueDecl>(arg.getAsDecl());
1143 
1144       // Find the instantiation of the template argument.  This is
1145       // required for nested templates.
1146       VD = cast_or_null<ValueDecl>(
1147              getSema().FindInstantiatedDecl(loc, VD, TemplateArgs));
1148       if (!VD)
1149         return ExprError();
1150     } else {
1151       // Propagate NULL template argument.
1152       VD = nullptr;
1153     }
1154 
1155     // Derive the type we want the substituted decl to have.  This had
1156     // better be non-dependent, or these checks will have serious problems.
1157     if (parm->isExpandedParameterPack()) {
1158       type = parm->getExpansionType(SemaRef.ArgumentPackSubstitutionIndex);
1159     } else if (parm->isParameterPack() &&
1160                isa<PackExpansionType>(parm->getType())) {
1161       type = SemaRef.SubstType(
1162                         cast<PackExpansionType>(parm->getType())->getPattern(),
1163                                      TemplateArgs, loc, parm->getDeclName());
1164     } else {
1165       type = SemaRef.SubstType(parm->getType(), TemplateArgs,
1166                                loc, parm->getDeclName());
1167     }
1168     assert(!type.isNull() && "type substitution failed for param type");
1169     assert(!type->isDependentType() && "param type still dependent");
1170     result = SemaRef.BuildExpressionFromDeclTemplateArgument(arg, type, loc);
1171 
1172     if (!result.isInvalid()) type = result.get()->getType();
1173   } else {
1174     result = SemaRef.BuildExpressionFromIntegralTemplateArgument(arg, loc);
1175 
1176     // Note that this type can be different from the type of 'result',
1177     // e.g. if it's an enum type.
1178     type = arg.getIntegralType();
1179   }
1180   if (result.isInvalid()) return ExprError();
1181 
1182   Expr *resultExpr = result.get();
1183   return new (SemaRef.Context) SubstNonTypeTemplateParmExpr(
1184       type, resultExpr->getValueKind(), loc, parm, resultExpr);
1185 }
1186 
1187 ExprResult
1188 TemplateInstantiator::TransformSubstNonTypeTemplateParmPackExpr(
1189                                           SubstNonTypeTemplateParmPackExpr *E) {
1190   if (getSema().ArgumentPackSubstitutionIndex == -1) {
1191     // We aren't expanding the parameter pack, so just return ourselves.
1192     return E;
1193   }
1194 
1195   TemplateArgument Arg = E->getArgumentPack();
1196   Arg = getPackSubstitutedTemplateArgument(getSema(), Arg);
1197   return transformNonTypeTemplateParmRef(E->getParameterPack(),
1198                                          E->getParameterPackLocation(),
1199                                          Arg);
1200 }
1201 
1202 ExprResult
1203 TemplateInstantiator::RebuildParmVarDeclRefExpr(ParmVarDecl *PD,
1204                                                 SourceLocation Loc) {
1205   DeclarationNameInfo NameInfo(PD->getDeclName(), Loc);
1206   return getSema().BuildDeclarationNameExpr(CXXScopeSpec(), NameInfo, PD);
1207 }
1208 
1209 ExprResult
1210 TemplateInstantiator::TransformFunctionParmPackExpr(FunctionParmPackExpr *E) {
1211   if (getSema().ArgumentPackSubstitutionIndex != -1) {
1212     // We can expand this parameter pack now.
1213     ParmVarDecl *D = E->getExpansion(getSema().ArgumentPackSubstitutionIndex);
1214     ValueDecl *VD = cast_or_null<ValueDecl>(TransformDecl(E->getExprLoc(), D));
1215     if (!VD)
1216       return ExprError();
1217     return RebuildParmVarDeclRefExpr(cast<ParmVarDecl>(VD), E->getExprLoc());
1218   }
1219 
1220   QualType T = TransformType(E->getType());
1221   if (T.isNull())
1222     return ExprError();
1223 
1224   // Transform each of the parameter expansions into the corresponding
1225   // parameters in the instantiation of the function decl.
1226   SmallVector<ParmVarDecl *, 8> Parms;
1227   Parms.reserve(E->getNumExpansions());
1228   for (FunctionParmPackExpr::iterator I = E->begin(), End = E->end();
1229        I != End; ++I) {
1230     ParmVarDecl *D =
1231         cast_or_null<ParmVarDecl>(TransformDecl(E->getExprLoc(), *I));
1232     if (!D)
1233       return ExprError();
1234     Parms.push_back(D);
1235   }
1236 
1237   return FunctionParmPackExpr::Create(getSema().Context, T,
1238                                       E->getParameterPack(),
1239                                       E->getParameterPackLocation(), Parms);
1240 }
1241 
1242 ExprResult
1243 TemplateInstantiator::TransformFunctionParmPackRefExpr(DeclRefExpr *E,
1244                                                        ParmVarDecl *PD) {
1245   typedef LocalInstantiationScope::DeclArgumentPack DeclArgumentPack;
1246   llvm::PointerUnion<Decl *, DeclArgumentPack *> *Found
1247     = getSema().CurrentInstantiationScope->findInstantiationOf(PD);
1248   assert(Found && "no instantiation for parameter pack");
1249 
1250   Decl *TransformedDecl;
1251   if (DeclArgumentPack *Pack = Found->dyn_cast<DeclArgumentPack *>()) {
1252     // If this is a reference to a function parameter pack which we can
1253     // substitute but can't yet expand, build a FunctionParmPackExpr for it.
1254     if (getSema().ArgumentPackSubstitutionIndex == -1) {
1255       QualType T = TransformType(E->getType());
1256       if (T.isNull())
1257         return ExprError();
1258       return FunctionParmPackExpr::Create(getSema().Context, T, PD,
1259                                           E->getExprLoc(), *Pack);
1260     }
1261 
1262     TransformedDecl = (*Pack)[getSema().ArgumentPackSubstitutionIndex];
1263   } else {
1264     TransformedDecl = Found->get<Decl*>();
1265   }
1266 
1267   // We have either an unexpanded pack or a specific expansion.
1268   return RebuildParmVarDeclRefExpr(cast<ParmVarDecl>(TransformedDecl),
1269                                    E->getExprLoc());
1270 }
1271 
1272 ExprResult
1273 TemplateInstantiator::TransformDeclRefExpr(DeclRefExpr *E) {
1274   NamedDecl *D = E->getDecl();
1275 
1276   // Handle references to non-type template parameters and non-type template
1277   // parameter packs.
1278   if (NonTypeTemplateParmDecl *NTTP = dyn_cast<NonTypeTemplateParmDecl>(D)) {
1279     if (NTTP->getDepth() < TemplateArgs.getNumLevels())
1280       return TransformTemplateParmRefExpr(E, NTTP);
1281 
1282     // We have a non-type template parameter that isn't fully substituted;
1283     // FindInstantiatedDecl will find it in the local instantiation scope.
1284   }
1285 
1286   // Handle references to function parameter packs.
1287   if (ParmVarDecl *PD = dyn_cast<ParmVarDecl>(D))
1288     if (PD->isParameterPack())
1289       return TransformFunctionParmPackRefExpr(E, PD);
1290 
1291   return TreeTransform<TemplateInstantiator>::TransformDeclRefExpr(E);
1292 }
1293 
1294 ExprResult TemplateInstantiator::TransformCXXDefaultArgExpr(
1295     CXXDefaultArgExpr *E) {
1296   assert(!cast<FunctionDecl>(E->getParam()->getDeclContext())->
1297              getDescribedFunctionTemplate() &&
1298          "Default arg expressions are never formed in dependent cases.");
1299   return SemaRef.BuildCXXDefaultArgExpr(E->getUsedLocation(),
1300                            cast<FunctionDecl>(E->getParam()->getDeclContext()),
1301                                         E->getParam());
1302 }
1303 
1304 template<typename Fn>
1305 QualType TemplateInstantiator::TransformFunctionProtoType(TypeLocBuilder &TLB,
1306                                  FunctionProtoTypeLoc TL,
1307                                  CXXRecordDecl *ThisContext,
1308                                  unsigned ThisTypeQuals,
1309                                  Fn TransformExceptionSpec) {
1310   // We need a local instantiation scope for this function prototype.
1311   LocalInstantiationScope Scope(SemaRef, /*CombineWithOuterScope=*/true);
1312   return inherited::TransformFunctionProtoType(
1313       TLB, TL, ThisContext, ThisTypeQuals, TransformExceptionSpec);
1314 }
1315 
1316 ParmVarDecl *
1317 TemplateInstantiator::TransformFunctionTypeParam(ParmVarDecl *OldParm,
1318                                                  int indexAdjustment,
1319                                                Optional<unsigned> NumExpansions,
1320                                                  bool ExpectParameterPack) {
1321   return SemaRef.SubstParmVarDecl(OldParm, TemplateArgs, indexAdjustment,
1322                                   NumExpansions, ExpectParameterPack);
1323 }
1324 
1325 QualType
1326 TemplateInstantiator::TransformTemplateTypeParmType(TypeLocBuilder &TLB,
1327                                                 TemplateTypeParmTypeLoc TL) {
1328   const TemplateTypeParmType *T = TL.getTypePtr();
1329   if (T->getDepth() < TemplateArgs.getNumLevels()) {
1330     // Replace the template type parameter with its corresponding
1331     // template argument.
1332 
1333     // If the corresponding template argument is NULL or doesn't exist, it's
1334     // because we are performing instantiation from explicitly-specified
1335     // template arguments in a function template class, but there were some
1336     // arguments left unspecified.
1337     if (!TemplateArgs.hasTemplateArgument(T->getDepth(), T->getIndex())) {
1338       TemplateTypeParmTypeLoc NewTL
1339         = TLB.push<TemplateTypeParmTypeLoc>(TL.getType());
1340       NewTL.setNameLoc(TL.getNameLoc());
1341       return TL.getType();
1342     }
1343 
1344     TemplateArgument Arg = TemplateArgs(T->getDepth(), T->getIndex());
1345 
1346     if (T->isParameterPack()) {
1347       assert(Arg.getKind() == TemplateArgument::Pack &&
1348              "Missing argument pack");
1349 
1350       if (getSema().ArgumentPackSubstitutionIndex == -1) {
1351         // We have the template argument pack, but we're not expanding the
1352         // enclosing pack expansion yet. Just save the template argument
1353         // pack for later substitution.
1354         QualType Result
1355           = getSema().Context.getSubstTemplateTypeParmPackType(T, Arg);
1356         SubstTemplateTypeParmPackTypeLoc NewTL
1357           = TLB.push<SubstTemplateTypeParmPackTypeLoc>(Result);
1358         NewTL.setNameLoc(TL.getNameLoc());
1359         return Result;
1360       }
1361 
1362       Arg = getPackSubstitutedTemplateArgument(getSema(), Arg);
1363     }
1364 
1365     assert(Arg.getKind() == TemplateArgument::Type &&
1366            "Template argument kind mismatch");
1367 
1368     QualType Replacement = Arg.getAsType();
1369 
1370     // TODO: only do this uniquing once, at the start of instantiation.
1371     QualType Result
1372       = getSema().Context.getSubstTemplateTypeParmType(T, Replacement);
1373     SubstTemplateTypeParmTypeLoc NewTL
1374       = TLB.push<SubstTemplateTypeParmTypeLoc>(Result);
1375     NewTL.setNameLoc(TL.getNameLoc());
1376     return Result;
1377   }
1378 
1379   // The template type parameter comes from an inner template (e.g.,
1380   // the template parameter list of a member template inside the
1381   // template we are instantiating). Create a new template type
1382   // parameter with the template "level" reduced by one.
1383   TemplateTypeParmDecl *NewTTPDecl = nullptr;
1384   if (TemplateTypeParmDecl *OldTTPDecl = T->getDecl())
1385     NewTTPDecl = cast_or_null<TemplateTypeParmDecl>(
1386                                   TransformDecl(TL.getNameLoc(), OldTTPDecl));
1387 
1388   QualType Result
1389     = getSema().Context.getTemplateTypeParmType(T->getDepth()
1390                                                  - TemplateArgs.getNumLevels(),
1391                                                 T->getIndex(),
1392                                                 T->isParameterPack(),
1393                                                 NewTTPDecl);
1394   TemplateTypeParmTypeLoc NewTL = TLB.push<TemplateTypeParmTypeLoc>(Result);
1395   NewTL.setNameLoc(TL.getNameLoc());
1396   return Result;
1397 }
1398 
1399 QualType
1400 TemplateInstantiator::TransformSubstTemplateTypeParmPackType(
1401                                                             TypeLocBuilder &TLB,
1402                                          SubstTemplateTypeParmPackTypeLoc TL) {
1403   if (getSema().ArgumentPackSubstitutionIndex == -1) {
1404     // We aren't expanding the parameter pack, so just return ourselves.
1405     SubstTemplateTypeParmPackTypeLoc NewTL
1406       = TLB.push<SubstTemplateTypeParmPackTypeLoc>(TL.getType());
1407     NewTL.setNameLoc(TL.getNameLoc());
1408     return TL.getType();
1409   }
1410 
1411   TemplateArgument Arg = TL.getTypePtr()->getArgumentPack();
1412   Arg = getPackSubstitutedTemplateArgument(getSema(), Arg);
1413   QualType Result = Arg.getAsType();
1414 
1415   Result = getSema().Context.getSubstTemplateTypeParmType(
1416                                       TL.getTypePtr()->getReplacedParameter(),
1417                                                           Result);
1418   SubstTemplateTypeParmTypeLoc NewTL
1419     = TLB.push<SubstTemplateTypeParmTypeLoc>(Result);
1420   NewTL.setNameLoc(TL.getNameLoc());
1421   return Result;
1422 }
1423 
1424 /// \brief Perform substitution on the type T with a given set of template
1425 /// arguments.
1426 ///
1427 /// This routine substitutes the given template arguments into the
1428 /// type T and produces the instantiated type.
1429 ///
1430 /// \param T the type into which the template arguments will be
1431 /// substituted. If this type is not dependent, it will be returned
1432 /// immediately.
1433 ///
1434 /// \param Args the template arguments that will be
1435 /// substituted for the top-level template parameters within T.
1436 ///
1437 /// \param Loc the location in the source code where this substitution
1438 /// is being performed. It will typically be the location of the
1439 /// declarator (if we're instantiating the type of some declaration)
1440 /// or the location of the type in the source code (if, e.g., we're
1441 /// instantiating the type of a cast expression).
1442 ///
1443 /// \param Entity the name of the entity associated with a declaration
1444 /// being instantiated (if any). May be empty to indicate that there
1445 /// is no such entity (if, e.g., this is a type that occurs as part of
1446 /// a cast expression) or that the entity has no name (e.g., an
1447 /// unnamed function parameter).
1448 ///
1449 /// \returns If the instantiation succeeds, the instantiated
1450 /// type. Otherwise, produces diagnostics and returns a NULL type.
1451 TypeSourceInfo *Sema::SubstType(TypeSourceInfo *T,
1452                                 const MultiLevelTemplateArgumentList &Args,
1453                                 SourceLocation Loc,
1454                                 DeclarationName Entity) {
1455   assert(!ActiveTemplateInstantiations.empty() &&
1456          "Cannot perform an instantiation without some context on the "
1457          "instantiation stack");
1458 
1459   if (!T->getType()->isInstantiationDependentType() &&
1460       !T->getType()->isVariablyModifiedType())
1461     return T;
1462 
1463   TemplateInstantiator Instantiator(*this, Args, Loc, Entity);
1464   return Instantiator.TransformType(T);
1465 }
1466 
1467 TypeSourceInfo *Sema::SubstType(TypeLoc TL,
1468                                 const MultiLevelTemplateArgumentList &Args,
1469                                 SourceLocation Loc,
1470                                 DeclarationName Entity) {
1471   assert(!ActiveTemplateInstantiations.empty() &&
1472          "Cannot perform an instantiation without some context on the "
1473          "instantiation stack");
1474 
1475   if (TL.getType().isNull())
1476     return nullptr;
1477 
1478   if (!TL.getType()->isInstantiationDependentType() &&
1479       !TL.getType()->isVariablyModifiedType()) {
1480     // FIXME: Make a copy of the TypeLoc data here, so that we can
1481     // return a new TypeSourceInfo. Inefficient!
1482     TypeLocBuilder TLB;
1483     TLB.pushFullCopy(TL);
1484     return TLB.getTypeSourceInfo(Context, TL.getType());
1485   }
1486 
1487   TemplateInstantiator Instantiator(*this, Args, Loc, Entity);
1488   TypeLocBuilder TLB;
1489   TLB.reserve(TL.getFullDataSize());
1490   QualType Result = Instantiator.TransformType(TLB, TL);
1491   if (Result.isNull())
1492     return nullptr;
1493 
1494   return TLB.getTypeSourceInfo(Context, Result);
1495 }
1496 
1497 /// Deprecated form of the above.
1498 QualType Sema::SubstType(QualType T,
1499                          const MultiLevelTemplateArgumentList &TemplateArgs,
1500                          SourceLocation Loc, DeclarationName Entity) {
1501   assert(!ActiveTemplateInstantiations.empty() &&
1502          "Cannot perform an instantiation without some context on the "
1503          "instantiation stack");
1504 
1505   // If T is not a dependent type or a variably-modified type, there
1506   // is nothing to do.
1507   if (!T->isInstantiationDependentType() && !T->isVariablyModifiedType())
1508     return T;
1509 
1510   TemplateInstantiator Instantiator(*this, TemplateArgs, Loc, Entity);
1511   return Instantiator.TransformType(T);
1512 }
1513 
1514 static bool NeedsInstantiationAsFunctionType(TypeSourceInfo *T) {
1515   if (T->getType()->isInstantiationDependentType() ||
1516       T->getType()->isVariablyModifiedType())
1517     return true;
1518 
1519   TypeLoc TL = T->getTypeLoc().IgnoreParens();
1520   if (!TL.getAs<FunctionProtoTypeLoc>())
1521     return false;
1522 
1523   FunctionProtoTypeLoc FP = TL.castAs<FunctionProtoTypeLoc>();
1524   for (ParmVarDecl *P : FP.getParams()) {
1525     // This must be synthesized from a typedef.
1526     if (!P) continue;
1527 
1528     // If there are any parameters, a new TypeSourceInfo that refers to the
1529     // instantiated parameters must be built.
1530     return true;
1531   }
1532 
1533   return false;
1534 }
1535 
1536 /// A form of SubstType intended specifically for instantiating the
1537 /// type of a FunctionDecl.  Its purpose is solely to force the
1538 /// instantiation of default-argument expressions and to avoid
1539 /// instantiating an exception-specification.
1540 TypeSourceInfo *Sema::SubstFunctionDeclType(TypeSourceInfo *T,
1541                                 const MultiLevelTemplateArgumentList &Args,
1542                                 SourceLocation Loc,
1543                                 DeclarationName Entity,
1544                                 CXXRecordDecl *ThisContext,
1545                                 unsigned ThisTypeQuals) {
1546   assert(!ActiveTemplateInstantiations.empty() &&
1547          "Cannot perform an instantiation without some context on the "
1548          "instantiation stack");
1549 
1550   if (!NeedsInstantiationAsFunctionType(T))
1551     return T;
1552 
1553   TemplateInstantiator Instantiator(*this, Args, Loc, Entity);
1554 
1555   TypeLocBuilder TLB;
1556 
1557   TypeLoc TL = T->getTypeLoc();
1558   TLB.reserve(TL.getFullDataSize());
1559 
1560   QualType Result;
1561 
1562   if (FunctionProtoTypeLoc Proto =
1563           TL.IgnoreParens().getAs<FunctionProtoTypeLoc>()) {
1564     // Instantiate the type, other than its exception specification. The
1565     // exception specification is instantiated in InitFunctionInstantiation
1566     // once we've built the FunctionDecl.
1567     // FIXME: Set the exception specification to EST_Uninstantiated here,
1568     // instead of rebuilding the function type again later.
1569     Result = Instantiator.TransformFunctionProtoType(
1570         TLB, Proto, ThisContext, ThisTypeQuals,
1571         [](FunctionProtoType::ExceptionSpecInfo &ESI,
1572            bool &Changed) { return false; });
1573   } else {
1574     Result = Instantiator.TransformType(TLB, TL);
1575   }
1576   if (Result.isNull())
1577     return nullptr;
1578 
1579   return TLB.getTypeSourceInfo(Context, Result);
1580 }
1581 
1582 void Sema::SubstExceptionSpec(FunctionDecl *New, const FunctionProtoType *Proto,
1583                               const MultiLevelTemplateArgumentList &Args) {
1584   FunctionProtoType::ExceptionSpecInfo ESI =
1585       Proto->getExtProtoInfo().ExceptionSpec;
1586   assert(ESI.Type != EST_Uninstantiated);
1587 
1588   TemplateInstantiator Instantiator(*this, Args, New->getLocation(),
1589                                     New->getDeclName());
1590 
1591   SmallVector<QualType, 4> ExceptionStorage;
1592   bool Changed = false;
1593   if (Instantiator.TransformExceptionSpec(
1594           New->getTypeSourceInfo()->getTypeLoc().getLocEnd(), ESI,
1595           ExceptionStorage, Changed))
1596     // On error, recover by dropping the exception specification.
1597     ESI.Type = EST_None;
1598 
1599   UpdateExceptionSpec(New, ESI);
1600 }
1601 
1602 ParmVarDecl *Sema::SubstParmVarDecl(ParmVarDecl *OldParm,
1603                             const MultiLevelTemplateArgumentList &TemplateArgs,
1604                                     int indexAdjustment,
1605                                     Optional<unsigned> NumExpansions,
1606                                     bool ExpectParameterPack) {
1607   TypeSourceInfo *OldDI = OldParm->getTypeSourceInfo();
1608   TypeSourceInfo *NewDI = nullptr;
1609 
1610   TypeLoc OldTL = OldDI->getTypeLoc();
1611   if (PackExpansionTypeLoc ExpansionTL = OldTL.getAs<PackExpansionTypeLoc>()) {
1612 
1613     // We have a function parameter pack. Substitute into the pattern of the
1614     // expansion.
1615     NewDI = SubstType(ExpansionTL.getPatternLoc(), TemplateArgs,
1616                       OldParm->getLocation(), OldParm->getDeclName());
1617     if (!NewDI)
1618       return nullptr;
1619 
1620     if (NewDI->getType()->containsUnexpandedParameterPack()) {
1621       // We still have unexpanded parameter packs, which means that
1622       // our function parameter is still a function parameter pack.
1623       // Therefore, make its type a pack expansion type.
1624       NewDI = CheckPackExpansion(NewDI, ExpansionTL.getEllipsisLoc(),
1625                                  NumExpansions);
1626     } else if (ExpectParameterPack) {
1627       // We expected to get a parameter pack but didn't (because the type
1628       // itself is not a pack expansion type), so complain. This can occur when
1629       // the substitution goes through an alias template that "loses" the
1630       // pack expansion.
1631       Diag(OldParm->getLocation(),
1632            diag::err_function_parameter_pack_without_parameter_packs)
1633         << NewDI->getType();
1634       return nullptr;
1635     }
1636   } else {
1637     NewDI = SubstType(OldDI, TemplateArgs, OldParm->getLocation(),
1638                       OldParm->getDeclName());
1639   }
1640 
1641   if (!NewDI)
1642     return nullptr;
1643 
1644   if (NewDI->getType()->isVoidType()) {
1645     Diag(OldParm->getLocation(), diag::err_param_with_void_type);
1646     return nullptr;
1647   }
1648 
1649   ParmVarDecl *NewParm = CheckParameter(Context.getTranslationUnitDecl(),
1650                                         OldParm->getInnerLocStart(),
1651                                         OldParm->getLocation(),
1652                                         OldParm->getIdentifier(),
1653                                         NewDI->getType(), NewDI,
1654                                         OldParm->getStorageClass());
1655   if (!NewParm)
1656     return nullptr;
1657 
1658   // Mark the (new) default argument as uninstantiated (if any).
1659   if (OldParm->hasUninstantiatedDefaultArg()) {
1660     Expr *Arg = OldParm->getUninstantiatedDefaultArg();
1661     NewParm->setUninstantiatedDefaultArg(Arg);
1662   } else if (OldParm->hasUnparsedDefaultArg()) {
1663     NewParm->setUnparsedDefaultArg();
1664     UnparsedDefaultArgInstantiations[OldParm].push_back(NewParm);
1665   } else if (Expr *Arg = OldParm->getDefaultArg()) {
1666     FunctionDecl *OwningFunc = cast<FunctionDecl>(OldParm->getDeclContext());
1667     if (OwningFunc->isLexicallyWithinFunctionOrMethod()) {
1668       // Instantiate default arguments for methods of local classes (DR1484)
1669       // and non-defining declarations.
1670       Sema::ContextRAII SavedContext(*this, OwningFunc);
1671       LocalInstantiationScope Local(*this);
1672       ExprResult NewArg = SubstExpr(Arg, TemplateArgs);
1673       if (NewArg.isUsable()) {
1674         // It would be nice if we still had this.
1675         SourceLocation EqualLoc = NewArg.get()->getLocStart();
1676         SetParamDefaultArgument(NewParm, NewArg.get(), EqualLoc);
1677       }
1678     } else {
1679       // FIXME: if we non-lazily instantiated non-dependent default args for
1680       // non-dependent parameter types we could remove a bunch of duplicate
1681       // conversion warnings for such arguments.
1682       NewParm->setUninstantiatedDefaultArg(Arg);
1683     }
1684   }
1685 
1686   NewParm->setHasInheritedDefaultArg(OldParm->hasInheritedDefaultArg());
1687 
1688   if (OldParm->isParameterPack() && !NewParm->isParameterPack()) {
1689     // Add the new parameter to the instantiated parameter pack.
1690     CurrentInstantiationScope->InstantiatedLocalPackArg(OldParm, NewParm);
1691   } else {
1692     // Introduce an Old -> New mapping
1693     CurrentInstantiationScope->InstantiatedLocal(OldParm, NewParm);
1694   }
1695 
1696   // FIXME: OldParm may come from a FunctionProtoType, in which case CurContext
1697   // can be anything, is this right ?
1698   NewParm->setDeclContext(CurContext);
1699 
1700   NewParm->setScopeInfo(OldParm->getFunctionScopeDepth(),
1701                         OldParm->getFunctionScopeIndex() + indexAdjustment);
1702 
1703   InstantiateAttrs(TemplateArgs, OldParm, NewParm);
1704 
1705   return NewParm;
1706 }
1707 
1708 /// \brief Substitute the given template arguments into the given set of
1709 /// parameters, producing the set of parameter types that would be generated
1710 /// from such a substitution.
1711 bool Sema::SubstParmTypes(SourceLocation Loc,
1712                           ParmVarDecl **Params, unsigned NumParams,
1713                           const MultiLevelTemplateArgumentList &TemplateArgs,
1714                           SmallVectorImpl<QualType> &ParamTypes,
1715                           SmallVectorImpl<ParmVarDecl *> *OutParams) {
1716   assert(!ActiveTemplateInstantiations.empty() &&
1717          "Cannot perform an instantiation without some context on the "
1718          "instantiation stack");
1719 
1720   TemplateInstantiator Instantiator(*this, TemplateArgs, Loc,
1721                                     DeclarationName());
1722   return Instantiator.TransformFunctionTypeParams(Loc, Params, NumParams,
1723                                                   nullptr, ParamTypes,
1724                                                   OutParams);
1725 }
1726 
1727 /// \brief Perform substitution on the base class specifiers of the
1728 /// given class template specialization.
1729 ///
1730 /// Produces a diagnostic and returns true on error, returns false and
1731 /// attaches the instantiated base classes to the class template
1732 /// specialization if successful.
1733 bool
1734 Sema::SubstBaseSpecifiers(CXXRecordDecl *Instantiation,
1735                           CXXRecordDecl *Pattern,
1736                           const MultiLevelTemplateArgumentList &TemplateArgs) {
1737   bool Invalid = false;
1738   SmallVector<CXXBaseSpecifier*, 4> InstantiatedBases;
1739   for (const auto &Base : Pattern->bases()) {
1740     if (!Base.getType()->isDependentType()) {
1741       if (const CXXRecordDecl *RD = Base.getType()->getAsCXXRecordDecl()) {
1742         if (RD->isInvalidDecl())
1743           Instantiation->setInvalidDecl();
1744       }
1745       InstantiatedBases.push_back(new (Context) CXXBaseSpecifier(Base));
1746       continue;
1747     }
1748 
1749     SourceLocation EllipsisLoc;
1750     TypeSourceInfo *BaseTypeLoc;
1751     if (Base.isPackExpansion()) {
1752       // This is a pack expansion. See whether we should expand it now, or
1753       // wait until later.
1754       SmallVector<UnexpandedParameterPack, 2> Unexpanded;
1755       collectUnexpandedParameterPacks(Base.getTypeSourceInfo()->getTypeLoc(),
1756                                       Unexpanded);
1757       bool ShouldExpand = false;
1758       bool RetainExpansion = false;
1759       Optional<unsigned> NumExpansions;
1760       if (CheckParameterPacksForExpansion(Base.getEllipsisLoc(),
1761                                           Base.getSourceRange(),
1762                                           Unexpanded,
1763                                           TemplateArgs, ShouldExpand,
1764                                           RetainExpansion,
1765                                           NumExpansions)) {
1766         Invalid = true;
1767         continue;
1768       }
1769 
1770       // If we should expand this pack expansion now, do so.
1771       if (ShouldExpand) {
1772         for (unsigned I = 0; I != *NumExpansions; ++I) {
1773             Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(*this, I);
1774 
1775           TypeSourceInfo *BaseTypeLoc = SubstType(Base.getTypeSourceInfo(),
1776                                                   TemplateArgs,
1777                                               Base.getSourceRange().getBegin(),
1778                                                   DeclarationName());
1779           if (!BaseTypeLoc) {
1780             Invalid = true;
1781             continue;
1782           }
1783 
1784           if (CXXBaseSpecifier *InstantiatedBase
1785                 = CheckBaseSpecifier(Instantiation,
1786                                      Base.getSourceRange(),
1787                                      Base.isVirtual(),
1788                                      Base.getAccessSpecifierAsWritten(),
1789                                      BaseTypeLoc,
1790                                      SourceLocation()))
1791             InstantiatedBases.push_back(InstantiatedBase);
1792           else
1793             Invalid = true;
1794         }
1795 
1796         continue;
1797       }
1798 
1799       // The resulting base specifier will (still) be a pack expansion.
1800       EllipsisLoc = Base.getEllipsisLoc();
1801       Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(*this, -1);
1802       BaseTypeLoc = SubstType(Base.getTypeSourceInfo(),
1803                               TemplateArgs,
1804                               Base.getSourceRange().getBegin(),
1805                               DeclarationName());
1806     } else {
1807       BaseTypeLoc = SubstType(Base.getTypeSourceInfo(),
1808                               TemplateArgs,
1809                               Base.getSourceRange().getBegin(),
1810                               DeclarationName());
1811     }
1812 
1813     if (!BaseTypeLoc) {
1814       Invalid = true;
1815       continue;
1816     }
1817 
1818     if (CXXBaseSpecifier *InstantiatedBase
1819           = CheckBaseSpecifier(Instantiation,
1820                                Base.getSourceRange(),
1821                                Base.isVirtual(),
1822                                Base.getAccessSpecifierAsWritten(),
1823                                BaseTypeLoc,
1824                                EllipsisLoc))
1825       InstantiatedBases.push_back(InstantiatedBase);
1826     else
1827       Invalid = true;
1828   }
1829 
1830   if (!Invalid && AttachBaseSpecifiers(Instantiation, InstantiatedBases))
1831     Invalid = true;
1832 
1833   return Invalid;
1834 }
1835 
1836 // Defined via #include from SemaTemplateInstantiateDecl.cpp
1837 namespace clang {
1838   namespace sema {
1839     Attr *instantiateTemplateAttribute(const Attr *At, ASTContext &C, Sema &S,
1840                             const MultiLevelTemplateArgumentList &TemplateArgs);
1841   }
1842 }
1843 
1844 /// Determine whether we would be unable to instantiate this template (because
1845 /// it either has no definition, or is in the process of being instantiated).
1846 static bool DiagnoseUninstantiableTemplate(Sema &S,
1847                                            SourceLocation PointOfInstantiation,
1848                                            TagDecl *Instantiation,
1849                                            bool InstantiatedFromMember,
1850                                            TagDecl *Pattern,
1851                                            TagDecl *PatternDef,
1852                                            TemplateSpecializationKind TSK,
1853                                            bool Complain = true) {
1854   if (PatternDef && !PatternDef->isBeingDefined())
1855     return false;
1856 
1857   if (!Complain || (PatternDef && PatternDef->isInvalidDecl())) {
1858     // Say nothing
1859   } else if (PatternDef) {
1860     assert(PatternDef->isBeingDefined());
1861     S.Diag(PointOfInstantiation,
1862            diag::err_template_instantiate_within_definition)
1863       << (TSK != TSK_ImplicitInstantiation)
1864       << S.Context.getTypeDeclType(Instantiation);
1865     // Not much point in noting the template declaration here, since
1866     // we're lexically inside it.
1867     Instantiation->setInvalidDecl();
1868   } else if (InstantiatedFromMember) {
1869     S.Diag(PointOfInstantiation,
1870            diag::err_implicit_instantiate_member_undefined)
1871       << S.Context.getTypeDeclType(Instantiation);
1872     S.Diag(Pattern->getLocation(), diag::note_member_declared_at);
1873   } else {
1874     S.Diag(PointOfInstantiation, diag::err_template_instantiate_undefined)
1875       << (TSK != TSK_ImplicitInstantiation)
1876       << S.Context.getTypeDeclType(Instantiation);
1877     S.Diag(Pattern->getLocation(), diag::note_template_decl_here);
1878   }
1879 
1880   // In general, Instantiation isn't marked invalid to get more than one
1881   // error for multiple undefined instantiations. But the code that does
1882   // explicit declaration -> explicit definition conversion can't handle
1883   // invalid declarations, so mark as invalid in that case.
1884   if (TSK == TSK_ExplicitInstantiationDeclaration)
1885     Instantiation->setInvalidDecl();
1886   return true;
1887 }
1888 
1889 /// \brief Instantiate the definition of a class from a given pattern.
1890 ///
1891 /// \param PointOfInstantiation The point of instantiation within the
1892 /// source code.
1893 ///
1894 /// \param Instantiation is the declaration whose definition is being
1895 /// instantiated. This will be either a class template specialization
1896 /// or a member class of a class template specialization.
1897 ///
1898 /// \param Pattern is the pattern from which the instantiation
1899 /// occurs. This will be either the declaration of a class template or
1900 /// the declaration of a member class of a class template.
1901 ///
1902 /// \param TemplateArgs The template arguments to be substituted into
1903 /// the pattern.
1904 ///
1905 /// \param TSK the kind of implicit or explicit instantiation to perform.
1906 ///
1907 /// \param Complain whether to complain if the class cannot be instantiated due
1908 /// to the lack of a definition.
1909 ///
1910 /// \returns true if an error occurred, false otherwise.
1911 bool
1912 Sema::InstantiateClass(SourceLocation PointOfInstantiation,
1913                        CXXRecordDecl *Instantiation, CXXRecordDecl *Pattern,
1914                        const MultiLevelTemplateArgumentList &TemplateArgs,
1915                        TemplateSpecializationKind TSK,
1916                        bool Complain) {
1917   CXXRecordDecl *PatternDef
1918     = cast_or_null<CXXRecordDecl>(Pattern->getDefinition());
1919   if (DiagnoseUninstantiableTemplate(*this, PointOfInstantiation, Instantiation,
1920                                 Instantiation->getInstantiatedFromMemberClass(),
1921                                      Pattern, PatternDef, TSK, Complain))
1922     return true;
1923   Pattern = PatternDef;
1924 
1925   // \brief Record the point of instantiation.
1926   if (MemberSpecializationInfo *MSInfo
1927         = Instantiation->getMemberSpecializationInfo()) {
1928     MSInfo->setTemplateSpecializationKind(TSK);
1929     MSInfo->setPointOfInstantiation(PointOfInstantiation);
1930   } else if (ClassTemplateSpecializationDecl *Spec
1931         = dyn_cast<ClassTemplateSpecializationDecl>(Instantiation)) {
1932     Spec->setTemplateSpecializationKind(TSK);
1933     Spec->setPointOfInstantiation(PointOfInstantiation);
1934   }
1935 
1936   InstantiatingTemplate Inst(*this, PointOfInstantiation, Instantiation);
1937   if (Inst.isInvalid())
1938     return true;
1939 
1940   // Enter the scope of this instantiation. We don't use
1941   // PushDeclContext because we don't have a scope.
1942   ContextRAII SavedContext(*this, Instantiation);
1943   EnterExpressionEvaluationContext EvalContext(*this,
1944                                                Sema::PotentiallyEvaluated);
1945 
1946   // If this is an instantiation of a local class, merge this local
1947   // instantiation scope with the enclosing scope. Otherwise, every
1948   // instantiation of a class has its own local instantiation scope.
1949   bool MergeWithParentScope = !Instantiation->isDefinedOutsideFunctionOrMethod();
1950   LocalInstantiationScope Scope(*this, MergeWithParentScope);
1951 
1952   // Pull attributes from the pattern onto the instantiation.
1953   InstantiateAttrs(TemplateArgs, Pattern, Instantiation);
1954 
1955   // Start the definition of this instantiation.
1956   Instantiation->startDefinition();
1957 
1958   // The instantiation is visible here, even if it was first declared in an
1959   // unimported module.
1960   Instantiation->setHidden(false);
1961 
1962   // FIXME: This loses the as-written tag kind for an explicit instantiation.
1963   Instantiation->setTagKind(Pattern->getTagKind());
1964 
1965   // Do substitution on the base class specifiers.
1966   if (SubstBaseSpecifiers(Instantiation, Pattern, TemplateArgs))
1967     Instantiation->setInvalidDecl();
1968 
1969   TemplateDeclInstantiator Instantiator(*this, Instantiation, TemplateArgs);
1970   SmallVector<Decl*, 4> Fields;
1971   // Delay instantiation of late parsed attributes.
1972   LateInstantiatedAttrVec LateAttrs;
1973   Instantiator.enableLateAttributeInstantiation(&LateAttrs);
1974 
1975   for (auto *Member : Pattern->decls()) {
1976     // Don't instantiate members not belonging in this semantic context.
1977     // e.g. for:
1978     // @code
1979     //    template <int i> class A {
1980     //      class B *g;
1981     //    };
1982     // @endcode
1983     // 'class B' has the template as lexical context but semantically it is
1984     // introduced in namespace scope.
1985     if (Member->getDeclContext() != Pattern)
1986       continue;
1987 
1988     if (Member->isInvalidDecl()) {
1989       Instantiation->setInvalidDecl();
1990       continue;
1991     }
1992 
1993     Decl *NewMember = Instantiator.Visit(Member);
1994     if (NewMember) {
1995       if (FieldDecl *Field = dyn_cast<FieldDecl>(NewMember)) {
1996         Fields.push_back(Field);
1997       } else if (EnumDecl *Enum = dyn_cast<EnumDecl>(NewMember)) {
1998         // C++11 [temp.inst]p1: The implicit instantiation of a class template
1999         // specialization causes the implicit instantiation of the definitions
2000         // of unscoped member enumerations.
2001         // Record a point of instantiation for this implicit instantiation.
2002         if (TSK == TSK_ImplicitInstantiation && !Enum->isScoped() &&
2003             Enum->isCompleteDefinition()) {
2004           MemberSpecializationInfo *MSInfo =Enum->getMemberSpecializationInfo();
2005           assert(MSInfo && "no spec info for member enum specialization");
2006           MSInfo->setTemplateSpecializationKind(TSK_ImplicitInstantiation);
2007           MSInfo->setPointOfInstantiation(PointOfInstantiation);
2008         }
2009       } else if (StaticAssertDecl *SA = dyn_cast<StaticAssertDecl>(NewMember)) {
2010         if (SA->isFailed()) {
2011           // A static_assert failed. Bail out; instantiating this
2012           // class is probably not meaningful.
2013           Instantiation->setInvalidDecl();
2014           break;
2015         }
2016       }
2017 
2018       if (NewMember->isInvalidDecl())
2019         Instantiation->setInvalidDecl();
2020     } else {
2021       // FIXME: Eventually, a NULL return will mean that one of the
2022       // instantiations was a semantic disaster, and we'll want to mark the
2023       // declaration invalid.
2024       // For now, we expect to skip some members that we can't yet handle.
2025     }
2026   }
2027 
2028   // Finish checking fields.
2029   ActOnFields(nullptr, Instantiation->getLocation(), Instantiation, Fields,
2030               SourceLocation(), SourceLocation(), nullptr);
2031   CheckCompletedCXXClass(Instantiation);
2032 
2033   // Default arguments are parsed, if not instantiated. We can go instantiate
2034   // default arg exprs for default constructors if necessary now.
2035   ActOnFinishCXXNonNestedClass(Instantiation);
2036 
2037   // Instantiate late parsed attributes, and attach them to their decls.
2038   // See Sema::InstantiateAttrs
2039   for (LateInstantiatedAttrVec::iterator I = LateAttrs.begin(),
2040        E = LateAttrs.end(); I != E; ++I) {
2041     assert(CurrentInstantiationScope == Instantiator.getStartingScope());
2042     CurrentInstantiationScope = I->Scope;
2043 
2044     // Allow 'this' within late-parsed attributes.
2045     NamedDecl *ND = dyn_cast<NamedDecl>(I->NewDecl);
2046     CXXRecordDecl *ThisContext =
2047         dyn_cast_or_null<CXXRecordDecl>(ND->getDeclContext());
2048     CXXThisScopeRAII ThisScope(*this, ThisContext, /*TypeQuals*/0,
2049                                ND && ND->isCXXInstanceMember());
2050 
2051     Attr *NewAttr =
2052       instantiateTemplateAttribute(I->TmplAttr, Context, *this, TemplateArgs);
2053     I->NewDecl->addAttr(NewAttr);
2054     LocalInstantiationScope::deleteScopes(I->Scope,
2055                                           Instantiator.getStartingScope());
2056   }
2057   Instantiator.disableLateAttributeInstantiation();
2058   LateAttrs.clear();
2059 
2060   ActOnFinishDelayedMemberInitializers(Instantiation);
2061 
2062   // FIXME: We should do something similar for explicit instantiations so they
2063   // end up in the right module.
2064   if (TSK == TSK_ImplicitInstantiation) {
2065     Instantiation->setLocation(Pattern->getLocation());
2066     Instantiation->setLocStart(Pattern->getInnerLocStart());
2067     Instantiation->setRBraceLoc(Pattern->getRBraceLoc());
2068   }
2069 
2070   if (!Instantiation->isInvalidDecl()) {
2071     // Perform any dependent diagnostics from the pattern.
2072     PerformDependentDiagnostics(Pattern, TemplateArgs);
2073 
2074     // Instantiate any out-of-line class template partial
2075     // specializations now.
2076     for (TemplateDeclInstantiator::delayed_partial_spec_iterator
2077               P = Instantiator.delayed_partial_spec_begin(),
2078            PEnd = Instantiator.delayed_partial_spec_end();
2079          P != PEnd; ++P) {
2080       if (!Instantiator.InstantiateClassTemplatePartialSpecialization(
2081               P->first, P->second)) {
2082         Instantiation->setInvalidDecl();
2083         break;
2084       }
2085     }
2086 
2087     // Instantiate any out-of-line variable template partial
2088     // specializations now.
2089     for (TemplateDeclInstantiator::delayed_var_partial_spec_iterator
2090               P = Instantiator.delayed_var_partial_spec_begin(),
2091            PEnd = Instantiator.delayed_var_partial_spec_end();
2092          P != PEnd; ++P) {
2093       if (!Instantiator.InstantiateVarTemplatePartialSpecialization(
2094               P->first, P->second)) {
2095         Instantiation->setInvalidDecl();
2096         break;
2097       }
2098     }
2099   }
2100 
2101   // Exit the scope of this instantiation.
2102   SavedContext.pop();
2103 
2104   if (!Instantiation->isInvalidDecl()) {
2105     Consumer.HandleTagDeclDefinition(Instantiation);
2106 
2107     // Always emit the vtable for an explicit instantiation definition
2108     // of a polymorphic class template specialization.
2109     if (TSK == TSK_ExplicitInstantiationDefinition)
2110       MarkVTableUsed(PointOfInstantiation, Instantiation, true);
2111   }
2112 
2113   return Instantiation->isInvalidDecl();
2114 }
2115 
2116 /// \brief Instantiate the definition of an enum from a given pattern.
2117 ///
2118 /// \param PointOfInstantiation The point of instantiation within the
2119 ///        source code.
2120 /// \param Instantiation is the declaration whose definition is being
2121 ///        instantiated. This will be a member enumeration of a class
2122 ///        temploid specialization, or a local enumeration within a
2123 ///        function temploid specialization.
2124 /// \param Pattern The templated declaration from which the instantiation
2125 ///        occurs.
2126 /// \param TemplateArgs The template arguments to be substituted into
2127 ///        the pattern.
2128 /// \param TSK The kind of implicit or explicit instantiation to perform.
2129 ///
2130 /// \return \c true if an error occurred, \c false otherwise.
2131 bool Sema::InstantiateEnum(SourceLocation PointOfInstantiation,
2132                            EnumDecl *Instantiation, EnumDecl *Pattern,
2133                            const MultiLevelTemplateArgumentList &TemplateArgs,
2134                            TemplateSpecializationKind TSK) {
2135   EnumDecl *PatternDef = Pattern->getDefinition();
2136   if (DiagnoseUninstantiableTemplate(*this, PointOfInstantiation, Instantiation,
2137                                  Instantiation->getInstantiatedFromMemberEnum(),
2138                                      Pattern, PatternDef, TSK,/*Complain*/true))
2139     return true;
2140   Pattern = PatternDef;
2141 
2142   // Record the point of instantiation.
2143   if (MemberSpecializationInfo *MSInfo
2144         = Instantiation->getMemberSpecializationInfo()) {
2145     MSInfo->setTemplateSpecializationKind(TSK);
2146     MSInfo->setPointOfInstantiation(PointOfInstantiation);
2147   }
2148 
2149   InstantiatingTemplate Inst(*this, PointOfInstantiation, Instantiation);
2150   if (Inst.isInvalid())
2151     return true;
2152 
2153   // The instantiation is visible here, even if it was first declared in an
2154   // unimported module.
2155   Instantiation->setHidden(false);
2156 
2157   // Enter the scope of this instantiation. We don't use
2158   // PushDeclContext because we don't have a scope.
2159   ContextRAII SavedContext(*this, Instantiation);
2160   EnterExpressionEvaluationContext EvalContext(*this,
2161                                                Sema::PotentiallyEvaluated);
2162 
2163   LocalInstantiationScope Scope(*this, /*MergeWithParentScope*/true);
2164 
2165   // Pull attributes from the pattern onto the instantiation.
2166   InstantiateAttrs(TemplateArgs, Pattern, Instantiation);
2167 
2168   TemplateDeclInstantiator Instantiator(*this, Instantiation, TemplateArgs);
2169   Instantiator.InstantiateEnumDefinition(Instantiation, Pattern);
2170 
2171   // Exit the scope of this instantiation.
2172   SavedContext.pop();
2173 
2174   return Instantiation->isInvalidDecl();
2175 }
2176 
2177 
2178 /// \brief Instantiate the definition of a field from the given pattern.
2179 ///
2180 /// \param PointOfInstantiation The point of instantiation within the
2181 ///        source code.
2182 /// \param Instantiation is the declaration whose definition is being
2183 ///        instantiated. This will be a class of a class temploid
2184 ///        specialization, or a local enumeration within a function temploid
2185 ///        specialization.
2186 /// \param Pattern The templated declaration from which the instantiation
2187 ///        occurs.
2188 /// \param TemplateArgs The template arguments to be substituted into
2189 ///        the pattern.
2190 ///
2191 /// \return \c true if an error occurred, \c false otherwise.
2192 bool Sema::InstantiateInClassInitializer(
2193     SourceLocation PointOfInstantiation, FieldDecl *Instantiation,
2194     FieldDecl *Pattern, const MultiLevelTemplateArgumentList &TemplateArgs) {
2195   // If there is no initializer, we don't need to do anything.
2196   if (!Pattern->hasInClassInitializer())
2197     return false;
2198 
2199   assert(Instantiation->getInClassInitStyle() ==
2200              Pattern->getInClassInitStyle() &&
2201          "pattern and instantiation disagree about init style");
2202 
2203   // Error out if we haven't parsed the initializer of the pattern yet because
2204   // we are waiting for the closing brace of the outer class.
2205   Expr *OldInit = Pattern->getInClassInitializer();
2206   if (!OldInit) {
2207     RecordDecl *PatternRD = Pattern->getParent();
2208     RecordDecl *OutermostClass = PatternRD->getOuterLexicalRecordContext();
2209     if (OutermostClass == PatternRD) {
2210       Diag(Pattern->getLocEnd(), diag::err_in_class_initializer_not_yet_parsed)
2211           << PatternRD << Pattern;
2212     } else {
2213       Diag(Pattern->getLocEnd(),
2214            diag::err_in_class_initializer_not_yet_parsed_outer_class)
2215           << PatternRD << OutermostClass << Pattern;
2216     }
2217     Instantiation->setInvalidDecl();
2218     return true;
2219   }
2220 
2221   InstantiatingTemplate Inst(*this, PointOfInstantiation, Instantiation);
2222   if (Inst.isInvalid())
2223     return true;
2224 
2225   // Enter the scope of this instantiation. We don't use PushDeclContext because
2226   // we don't have a scope.
2227   ContextRAII SavedContext(*this, Instantiation->getParent());
2228   EnterExpressionEvaluationContext EvalContext(*this,
2229                                                Sema::PotentiallyEvaluated);
2230 
2231   LocalInstantiationScope Scope(*this, true);
2232 
2233   // Instantiate the initializer.
2234   ActOnStartCXXInClassMemberInitializer();
2235   CXXThisScopeRAII ThisScope(*this, Instantiation->getParent(), /*TypeQuals=*/0);
2236 
2237   ExprResult NewInit = SubstInitializer(OldInit, TemplateArgs,
2238                                         /*CXXDirectInit=*/false);
2239   Expr *Init = NewInit.get();
2240   assert((!Init || !isa<ParenListExpr>(Init)) && "call-style init in class");
2241   ActOnFinishCXXInClassMemberInitializer(
2242       Instantiation, Init ? Init->getLocStart() : SourceLocation(), Init);
2243 
2244   // Exit the scope of this instantiation.
2245   SavedContext.pop();
2246 
2247   // Return true if the in-class initializer is still missing.
2248   return !Instantiation->getInClassInitializer();
2249 }
2250 
2251 namespace {
2252   /// \brief A partial specialization whose template arguments have matched
2253   /// a given template-id.
2254   struct PartialSpecMatchResult {
2255     ClassTemplatePartialSpecializationDecl *Partial;
2256     TemplateArgumentList *Args;
2257   };
2258 }
2259 
2260 bool Sema::InstantiateClassTemplateSpecialization(
2261     SourceLocation PointOfInstantiation,
2262     ClassTemplateSpecializationDecl *ClassTemplateSpec,
2263     TemplateSpecializationKind TSK, bool Complain) {
2264   // Perform the actual instantiation on the canonical declaration.
2265   ClassTemplateSpec = cast<ClassTemplateSpecializationDecl>(
2266                                          ClassTemplateSpec->getCanonicalDecl());
2267   if (ClassTemplateSpec->isInvalidDecl())
2268     return true;
2269 
2270   ClassTemplateDecl *Template = ClassTemplateSpec->getSpecializedTemplate();
2271   CXXRecordDecl *Pattern = nullptr;
2272 
2273   // C++ [temp.class.spec.match]p1:
2274   //   When a class template is used in a context that requires an
2275   //   instantiation of the class, it is necessary to determine
2276   //   whether the instantiation is to be generated using the primary
2277   //   template or one of the partial specializations. This is done by
2278   //   matching the template arguments of the class template
2279   //   specialization with the template argument lists of the partial
2280   //   specializations.
2281   typedef PartialSpecMatchResult MatchResult;
2282   SmallVector<MatchResult, 4> Matched;
2283   SmallVector<ClassTemplatePartialSpecializationDecl *, 4> PartialSpecs;
2284   Template->getPartialSpecializations(PartialSpecs);
2285   TemplateSpecCandidateSet FailedCandidates(PointOfInstantiation);
2286   for (unsigned I = 0, N = PartialSpecs.size(); I != N; ++I) {
2287     ClassTemplatePartialSpecializationDecl *Partial = PartialSpecs[I];
2288     TemplateDeductionInfo Info(FailedCandidates.getLocation());
2289     if (TemplateDeductionResult Result
2290           = DeduceTemplateArguments(Partial,
2291                                     ClassTemplateSpec->getTemplateArgs(),
2292                                     Info)) {
2293       // Store the failed-deduction information for use in diagnostics, later.
2294       // TODO: Actually use the failed-deduction info?
2295       FailedCandidates.addCandidate()
2296           .set(Partial, MakeDeductionFailureInfo(Context, Result, Info));
2297       (void)Result;
2298     } else {
2299       Matched.push_back(PartialSpecMatchResult());
2300       Matched.back().Partial = Partial;
2301       Matched.back().Args = Info.take();
2302     }
2303   }
2304 
2305   // If we're dealing with a member template where the template parameters
2306   // have been instantiated, this provides the original template parameters
2307   // from which the member template's parameters were instantiated.
2308 
2309   if (Matched.size() >= 1) {
2310     SmallVectorImpl<MatchResult>::iterator Best = Matched.begin();
2311     if (Matched.size() == 1) {
2312       //   -- If exactly one matching specialization is found, the
2313       //      instantiation is generated from that specialization.
2314       // We don't need to do anything for this.
2315     } else {
2316       //   -- If more than one matching specialization is found, the
2317       //      partial order rules (14.5.4.2) are used to determine
2318       //      whether one of the specializations is more specialized
2319       //      than the others. If none of the specializations is more
2320       //      specialized than all of the other matching
2321       //      specializations, then the use of the class template is
2322       //      ambiguous and the program is ill-formed.
2323       for (SmallVectorImpl<MatchResult>::iterator P = Best + 1,
2324                                                PEnd = Matched.end();
2325            P != PEnd; ++P) {
2326         if (getMoreSpecializedPartialSpecialization(P->Partial, Best->Partial,
2327                                                     PointOfInstantiation)
2328               == P->Partial)
2329           Best = P;
2330       }
2331 
2332       // Determine if the best partial specialization is more specialized than
2333       // the others.
2334       bool Ambiguous = false;
2335       for (SmallVectorImpl<MatchResult>::iterator P = Matched.begin(),
2336                                                PEnd = Matched.end();
2337            P != PEnd; ++P) {
2338         if (P != Best &&
2339             getMoreSpecializedPartialSpecialization(P->Partial, Best->Partial,
2340                                                     PointOfInstantiation)
2341               != Best->Partial) {
2342           Ambiguous = true;
2343           break;
2344         }
2345       }
2346 
2347       if (Ambiguous) {
2348         // Partial ordering did not produce a clear winner. Complain.
2349         ClassTemplateSpec->setInvalidDecl();
2350         Diag(PointOfInstantiation, diag::err_partial_spec_ordering_ambiguous)
2351           << ClassTemplateSpec;
2352 
2353         // Print the matching partial specializations.
2354         for (SmallVectorImpl<MatchResult>::iterator P = Matched.begin(),
2355                                                  PEnd = Matched.end();
2356              P != PEnd; ++P)
2357           Diag(P->Partial->getLocation(), diag::note_partial_spec_match)
2358             << getTemplateArgumentBindingsText(
2359                                             P->Partial->getTemplateParameters(),
2360                                                *P->Args);
2361 
2362         return true;
2363       }
2364     }
2365 
2366     // Instantiate using the best class template partial specialization.
2367     ClassTemplatePartialSpecializationDecl *OrigPartialSpec = Best->Partial;
2368     while (OrigPartialSpec->getInstantiatedFromMember()) {
2369       // If we've found an explicit specialization of this class template,
2370       // stop here and use that as the pattern.
2371       if (OrigPartialSpec->isMemberSpecialization())
2372         break;
2373 
2374       OrigPartialSpec = OrigPartialSpec->getInstantiatedFromMember();
2375     }
2376 
2377     Pattern = OrigPartialSpec;
2378     ClassTemplateSpec->setInstantiationOf(Best->Partial, Best->Args);
2379   } else {
2380     //   -- If no matches are found, the instantiation is generated
2381     //      from the primary template.
2382     ClassTemplateDecl *OrigTemplate = Template;
2383     while (OrigTemplate->getInstantiatedFromMemberTemplate()) {
2384       // If we've found an explicit specialization of this class template,
2385       // stop here and use that as the pattern.
2386       if (OrigTemplate->isMemberSpecialization())
2387         break;
2388 
2389       OrigTemplate = OrigTemplate->getInstantiatedFromMemberTemplate();
2390     }
2391 
2392     Pattern = OrigTemplate->getTemplatedDecl();
2393   }
2394 
2395   bool Result = InstantiateClass(PointOfInstantiation, ClassTemplateSpec,
2396                                  Pattern,
2397                                 getTemplateInstantiationArgs(ClassTemplateSpec),
2398                                  TSK,
2399                                  Complain);
2400 
2401   return Result;
2402 }
2403 
2404 /// \brief Instantiates the definitions of all of the member
2405 /// of the given class, which is an instantiation of a class template
2406 /// or a member class of a template.
2407 void
2408 Sema::InstantiateClassMembers(SourceLocation PointOfInstantiation,
2409                               CXXRecordDecl *Instantiation,
2410                         const MultiLevelTemplateArgumentList &TemplateArgs,
2411                               TemplateSpecializationKind TSK) {
2412   // FIXME: We need to notify the ASTMutationListener that we did all of these
2413   // things, in case we have an explicit instantiation definition in a PCM, a
2414   // module, or preamble, and the declaration is in an imported AST.
2415   assert(
2416       (TSK == TSK_ExplicitInstantiationDefinition ||
2417        TSK == TSK_ExplicitInstantiationDeclaration ||
2418        (TSK == TSK_ImplicitInstantiation && Instantiation->isLocalClass())) &&
2419       "Unexpected template specialization kind!");
2420   for (auto *D : Instantiation->decls()) {
2421     bool SuppressNew = false;
2422     if (auto *Function = dyn_cast<FunctionDecl>(D)) {
2423       if (FunctionDecl *Pattern
2424             = Function->getInstantiatedFromMemberFunction()) {
2425         MemberSpecializationInfo *MSInfo
2426           = Function->getMemberSpecializationInfo();
2427         assert(MSInfo && "No member specialization information?");
2428         if (MSInfo->getTemplateSpecializationKind()
2429                                                  == TSK_ExplicitSpecialization)
2430           continue;
2431 
2432         if (CheckSpecializationInstantiationRedecl(PointOfInstantiation, TSK,
2433                                                    Function,
2434                                         MSInfo->getTemplateSpecializationKind(),
2435                                               MSInfo->getPointOfInstantiation(),
2436                                                    SuppressNew) ||
2437             SuppressNew)
2438           continue;
2439 
2440         // C++11 [temp.explicit]p8:
2441         //   An explicit instantiation definition that names a class template
2442         //   specialization explicitly instantiates the class template
2443         //   specialization and is only an explicit instantiation definition
2444         //   of members whose definition is visible at the point of
2445         //   instantiation.
2446         if (TSK == TSK_ExplicitInstantiationDefinition && !Pattern->isDefined())
2447           continue;
2448 
2449         Function->setTemplateSpecializationKind(TSK, PointOfInstantiation);
2450 
2451         if (Function->isDefined()) {
2452           // Let the ASTConsumer know that this function has been explicitly
2453           // instantiated now, and its linkage might have changed.
2454           Consumer.HandleTopLevelDecl(DeclGroupRef(Function));
2455         } else if (TSK == TSK_ExplicitInstantiationDefinition) {
2456           InstantiateFunctionDefinition(PointOfInstantiation, Function);
2457         } else if (TSK == TSK_ImplicitInstantiation) {
2458           PendingLocalImplicitInstantiations.push_back(
2459               std::make_pair(Function, PointOfInstantiation));
2460         }
2461       }
2462     } else if (auto *Var = dyn_cast<VarDecl>(D)) {
2463       if (isa<VarTemplateSpecializationDecl>(Var))
2464         continue;
2465 
2466       if (Var->isStaticDataMember()) {
2467         MemberSpecializationInfo *MSInfo = Var->getMemberSpecializationInfo();
2468         assert(MSInfo && "No member specialization information?");
2469         if (MSInfo->getTemplateSpecializationKind()
2470                                                  == TSK_ExplicitSpecialization)
2471           continue;
2472 
2473         if (CheckSpecializationInstantiationRedecl(PointOfInstantiation, TSK,
2474                                                    Var,
2475                                         MSInfo->getTemplateSpecializationKind(),
2476                                               MSInfo->getPointOfInstantiation(),
2477                                                    SuppressNew) ||
2478             SuppressNew)
2479           continue;
2480 
2481         if (TSK == TSK_ExplicitInstantiationDefinition) {
2482           // C++0x [temp.explicit]p8:
2483           //   An explicit instantiation definition that names a class template
2484           //   specialization explicitly instantiates the class template
2485           //   specialization and is only an explicit instantiation definition
2486           //   of members whose definition is visible at the point of
2487           //   instantiation.
2488           if (!Var->getInstantiatedFromStaticDataMember()
2489                                                      ->getOutOfLineDefinition())
2490             continue;
2491 
2492           Var->setTemplateSpecializationKind(TSK, PointOfInstantiation);
2493           InstantiateStaticDataMemberDefinition(PointOfInstantiation, Var);
2494         } else {
2495           Var->setTemplateSpecializationKind(TSK, PointOfInstantiation);
2496         }
2497       }
2498     } else if (auto *Record = dyn_cast<CXXRecordDecl>(D)) {
2499       // Always skip the injected-class-name, along with any
2500       // redeclarations of nested classes, since both would cause us
2501       // to try to instantiate the members of a class twice.
2502       // Skip closure types; they'll get instantiated when we instantiate
2503       // the corresponding lambda-expression.
2504       if (Record->isInjectedClassName() || Record->getPreviousDecl() ||
2505           Record->isLambda())
2506         continue;
2507 
2508       MemberSpecializationInfo *MSInfo = Record->getMemberSpecializationInfo();
2509       assert(MSInfo && "No member specialization information?");
2510 
2511       if (MSInfo->getTemplateSpecializationKind()
2512                                                 == TSK_ExplicitSpecialization)
2513         continue;
2514 
2515       if (CheckSpecializationInstantiationRedecl(PointOfInstantiation, TSK,
2516                                                  Record,
2517                                         MSInfo->getTemplateSpecializationKind(),
2518                                               MSInfo->getPointOfInstantiation(),
2519                                                  SuppressNew) ||
2520           SuppressNew)
2521         continue;
2522 
2523       CXXRecordDecl *Pattern = Record->getInstantiatedFromMemberClass();
2524       assert(Pattern && "Missing instantiated-from-template information");
2525 
2526       if (!Record->getDefinition()) {
2527         if (!Pattern->getDefinition()) {
2528           // C++0x [temp.explicit]p8:
2529           //   An explicit instantiation definition that names a class template
2530           //   specialization explicitly instantiates the class template
2531           //   specialization and is only an explicit instantiation definition
2532           //   of members whose definition is visible at the point of
2533           //   instantiation.
2534           if (TSK == TSK_ExplicitInstantiationDeclaration) {
2535             MSInfo->setTemplateSpecializationKind(TSK);
2536             MSInfo->setPointOfInstantiation(PointOfInstantiation);
2537           }
2538 
2539           continue;
2540         }
2541 
2542         InstantiateClass(PointOfInstantiation, Record, Pattern,
2543                          TemplateArgs,
2544                          TSK);
2545       } else {
2546         if (TSK == TSK_ExplicitInstantiationDefinition &&
2547             Record->getTemplateSpecializationKind() ==
2548                 TSK_ExplicitInstantiationDeclaration) {
2549           Record->setTemplateSpecializationKind(TSK);
2550           MarkVTableUsed(PointOfInstantiation, Record, true);
2551         }
2552       }
2553 
2554       Pattern = cast_or_null<CXXRecordDecl>(Record->getDefinition());
2555       if (Pattern)
2556         InstantiateClassMembers(PointOfInstantiation, Pattern, TemplateArgs,
2557                                 TSK);
2558     } else if (auto *Enum = dyn_cast<EnumDecl>(D)) {
2559       MemberSpecializationInfo *MSInfo = Enum->getMemberSpecializationInfo();
2560       assert(MSInfo && "No member specialization information?");
2561 
2562       if (MSInfo->getTemplateSpecializationKind()
2563             == TSK_ExplicitSpecialization)
2564         continue;
2565 
2566       if (CheckSpecializationInstantiationRedecl(
2567             PointOfInstantiation, TSK, Enum,
2568             MSInfo->getTemplateSpecializationKind(),
2569             MSInfo->getPointOfInstantiation(), SuppressNew) ||
2570           SuppressNew)
2571         continue;
2572 
2573       if (Enum->getDefinition())
2574         continue;
2575 
2576       EnumDecl *Pattern = Enum->getInstantiatedFromMemberEnum();
2577       assert(Pattern && "Missing instantiated-from-template information");
2578 
2579       if (TSK == TSK_ExplicitInstantiationDefinition) {
2580         if (!Pattern->getDefinition())
2581           continue;
2582 
2583         InstantiateEnum(PointOfInstantiation, Enum, Pattern, TemplateArgs, TSK);
2584       } else {
2585         MSInfo->setTemplateSpecializationKind(TSK);
2586         MSInfo->setPointOfInstantiation(PointOfInstantiation);
2587       }
2588     } else if (auto *Field = dyn_cast<FieldDecl>(D)) {
2589       // No need to instantiate in-class initializers during explicit
2590       // instantiation.
2591       if (Field->hasInClassInitializer() && TSK == TSK_ImplicitInstantiation) {
2592         CXXRecordDecl *ClassPattern =
2593             Instantiation->getTemplateInstantiationPattern();
2594         DeclContext::lookup_result Lookup =
2595             ClassPattern->lookup(Field->getDeclName());
2596         assert(Lookup.size() == 1);
2597         FieldDecl *Pattern = cast<FieldDecl>(Lookup[0]);
2598         InstantiateInClassInitializer(PointOfInstantiation, Field, Pattern,
2599                                       TemplateArgs);
2600       }
2601     }
2602   }
2603 }
2604 
2605 /// \brief Instantiate the definitions of all of the members of the
2606 /// given class template specialization, which was named as part of an
2607 /// explicit instantiation.
2608 void
2609 Sema::InstantiateClassTemplateSpecializationMembers(
2610                                            SourceLocation PointOfInstantiation,
2611                             ClassTemplateSpecializationDecl *ClassTemplateSpec,
2612                                                TemplateSpecializationKind TSK) {
2613   // C++0x [temp.explicit]p7:
2614   //   An explicit instantiation that names a class template
2615   //   specialization is an explicit instantion of the same kind
2616   //   (declaration or definition) of each of its members (not
2617   //   including members inherited from base classes) that has not
2618   //   been previously explicitly specialized in the translation unit
2619   //   containing the explicit instantiation, except as described
2620   //   below.
2621   InstantiateClassMembers(PointOfInstantiation, ClassTemplateSpec,
2622                           getTemplateInstantiationArgs(ClassTemplateSpec),
2623                           TSK);
2624 }
2625 
2626 StmtResult
2627 Sema::SubstStmt(Stmt *S, const MultiLevelTemplateArgumentList &TemplateArgs) {
2628   if (!S)
2629     return S;
2630 
2631   TemplateInstantiator Instantiator(*this, TemplateArgs,
2632                                     SourceLocation(),
2633                                     DeclarationName());
2634   return Instantiator.TransformStmt(S);
2635 }
2636 
2637 ExprResult
2638 Sema::SubstExpr(Expr *E, const MultiLevelTemplateArgumentList &TemplateArgs) {
2639   if (!E)
2640     return E;
2641 
2642   TemplateInstantiator Instantiator(*this, TemplateArgs,
2643                                     SourceLocation(),
2644                                     DeclarationName());
2645   return Instantiator.TransformExpr(E);
2646 }
2647 
2648 ExprResult Sema::SubstInitializer(Expr *Init,
2649                           const MultiLevelTemplateArgumentList &TemplateArgs,
2650                           bool CXXDirectInit) {
2651   TemplateInstantiator Instantiator(*this, TemplateArgs,
2652                                     SourceLocation(),
2653                                     DeclarationName());
2654   return Instantiator.TransformInitializer(Init, CXXDirectInit);
2655 }
2656 
2657 bool Sema::SubstExprs(ArrayRef<Expr *> Exprs, bool IsCall,
2658                       const MultiLevelTemplateArgumentList &TemplateArgs,
2659                       SmallVectorImpl<Expr *> &Outputs) {
2660   if (Exprs.empty())
2661     return false;
2662 
2663   TemplateInstantiator Instantiator(*this, TemplateArgs,
2664                                     SourceLocation(),
2665                                     DeclarationName());
2666   return Instantiator.TransformExprs(Exprs.data(), Exprs.size(),
2667                                      IsCall, Outputs);
2668 }
2669 
2670 NestedNameSpecifierLoc
2671 Sema::SubstNestedNameSpecifierLoc(NestedNameSpecifierLoc NNS,
2672                         const MultiLevelTemplateArgumentList &TemplateArgs) {
2673   if (!NNS)
2674     return NestedNameSpecifierLoc();
2675 
2676   TemplateInstantiator Instantiator(*this, TemplateArgs, NNS.getBeginLoc(),
2677                                     DeclarationName());
2678   return Instantiator.TransformNestedNameSpecifierLoc(NNS);
2679 }
2680 
2681 /// \brief Do template substitution on declaration name info.
2682 DeclarationNameInfo
2683 Sema::SubstDeclarationNameInfo(const DeclarationNameInfo &NameInfo,
2684                          const MultiLevelTemplateArgumentList &TemplateArgs) {
2685   TemplateInstantiator Instantiator(*this, TemplateArgs, NameInfo.getLoc(),
2686                                     NameInfo.getName());
2687   return Instantiator.TransformDeclarationNameInfo(NameInfo);
2688 }
2689 
2690 TemplateName
2691 Sema::SubstTemplateName(NestedNameSpecifierLoc QualifierLoc,
2692                         TemplateName Name, SourceLocation Loc,
2693                         const MultiLevelTemplateArgumentList &TemplateArgs) {
2694   TemplateInstantiator Instantiator(*this, TemplateArgs, Loc,
2695                                     DeclarationName());
2696   CXXScopeSpec SS;
2697   SS.Adopt(QualifierLoc);
2698   return Instantiator.TransformTemplateName(SS, Name, Loc);
2699 }
2700 
2701 bool Sema::Subst(const TemplateArgumentLoc *Args, unsigned NumArgs,
2702                  TemplateArgumentListInfo &Result,
2703                  const MultiLevelTemplateArgumentList &TemplateArgs) {
2704   TemplateInstantiator Instantiator(*this, TemplateArgs, SourceLocation(),
2705                                     DeclarationName());
2706 
2707   return Instantiator.TransformTemplateArguments(Args, NumArgs, Result);
2708 }
2709 
2710 static const Decl *getCanonicalParmVarDecl(const Decl *D) {
2711   // When storing ParmVarDecls in the local instantiation scope, we always
2712   // want to use the ParmVarDecl from the canonical function declaration,
2713   // since the map is then valid for any redeclaration or definition of that
2714   // function.
2715   if (const ParmVarDecl *PV = dyn_cast<ParmVarDecl>(D)) {
2716     if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(PV->getDeclContext())) {
2717       unsigned i = PV->getFunctionScopeIndex();
2718       // This parameter might be from a freestanding function type within the
2719       // function and isn't necessarily referring to one of FD's parameters.
2720       if (FD->getParamDecl(i) == PV)
2721         return FD->getCanonicalDecl()->getParamDecl(i);
2722     }
2723   }
2724   return D;
2725 }
2726 
2727 
2728 llvm::PointerUnion<Decl *, LocalInstantiationScope::DeclArgumentPack *> *
2729 LocalInstantiationScope::findInstantiationOf(const Decl *D) {
2730   D = getCanonicalParmVarDecl(D);
2731   for (LocalInstantiationScope *Current = this; Current;
2732        Current = Current->Outer) {
2733 
2734     // Check if we found something within this scope.
2735     const Decl *CheckD = D;
2736     do {
2737       LocalDeclsMap::iterator Found = Current->LocalDecls.find(CheckD);
2738       if (Found != Current->LocalDecls.end())
2739         return &Found->second;
2740 
2741       // If this is a tag declaration, it's possible that we need to look for
2742       // a previous declaration.
2743       if (const TagDecl *Tag = dyn_cast<TagDecl>(CheckD))
2744         CheckD = Tag->getPreviousDecl();
2745       else
2746         CheckD = nullptr;
2747     } while (CheckD);
2748 
2749     // If we aren't combined with our outer scope, we're done.
2750     if (!Current->CombineWithOuterScope)
2751       break;
2752   }
2753 
2754   // If we're performing a partial substitution during template argument
2755   // deduction, we may not have values for template parameters yet.
2756   if (isa<NonTypeTemplateParmDecl>(D) || isa<TemplateTypeParmDecl>(D) ||
2757       isa<TemplateTemplateParmDecl>(D))
2758     return nullptr;
2759 
2760   // Local types referenced prior to definition may require instantiation.
2761   if (const CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(D))
2762     if (RD->isLocalClass())
2763       return nullptr;
2764 
2765   // Enumeration types referenced prior to definition may appear as a result of
2766   // error recovery.
2767   if (isa<EnumDecl>(D))
2768     return nullptr;
2769 
2770   // If we didn't find the decl, then we either have a sema bug, or we have a
2771   // forward reference to a label declaration.  Return null to indicate that
2772   // we have an uninstantiated label.
2773   assert(isa<LabelDecl>(D) && "declaration not instantiated in this scope");
2774   return nullptr;
2775 }
2776 
2777 void LocalInstantiationScope::InstantiatedLocal(const Decl *D, Decl *Inst) {
2778   D = getCanonicalParmVarDecl(D);
2779   llvm::PointerUnion<Decl *, DeclArgumentPack *> &Stored = LocalDecls[D];
2780   if (Stored.isNull()) {
2781 #ifndef NDEBUG
2782     // It should not be present in any surrounding scope either.
2783     LocalInstantiationScope *Current = this;
2784     while (Current->CombineWithOuterScope && Current->Outer) {
2785       Current = Current->Outer;
2786       assert(Current->LocalDecls.find(D) == Current->LocalDecls.end() &&
2787              "Instantiated local in inner and outer scopes");
2788     }
2789 #endif
2790     Stored = Inst;
2791   } else if (DeclArgumentPack *Pack = Stored.dyn_cast<DeclArgumentPack *>()) {
2792     Pack->push_back(cast<ParmVarDecl>(Inst));
2793   } else {
2794     assert(Stored.get<Decl *>() == Inst && "Already instantiated this local");
2795   }
2796 }
2797 
2798 void LocalInstantiationScope::InstantiatedLocalPackArg(const Decl *D,
2799                                                        ParmVarDecl *Inst) {
2800   D = getCanonicalParmVarDecl(D);
2801   DeclArgumentPack *Pack = LocalDecls[D].get<DeclArgumentPack *>();
2802   Pack->push_back(Inst);
2803 }
2804 
2805 void LocalInstantiationScope::MakeInstantiatedLocalArgPack(const Decl *D) {
2806 #ifndef NDEBUG
2807   // This should be the first time we've been told about this decl.
2808   for (LocalInstantiationScope *Current = this;
2809        Current && Current->CombineWithOuterScope; Current = Current->Outer)
2810     assert(Current->LocalDecls.find(D) == Current->LocalDecls.end() &&
2811            "Creating local pack after instantiation of local");
2812 #endif
2813 
2814   D = getCanonicalParmVarDecl(D);
2815   llvm::PointerUnion<Decl *, DeclArgumentPack *> &Stored = LocalDecls[D];
2816   DeclArgumentPack *Pack = new DeclArgumentPack;
2817   Stored = Pack;
2818   ArgumentPacks.push_back(Pack);
2819 }
2820 
2821 void LocalInstantiationScope::SetPartiallySubstitutedPack(NamedDecl *Pack,
2822                                           const TemplateArgument *ExplicitArgs,
2823                                                     unsigned NumExplicitArgs) {
2824   assert((!PartiallySubstitutedPack || PartiallySubstitutedPack == Pack) &&
2825          "Already have a partially-substituted pack");
2826   assert((!PartiallySubstitutedPack
2827           || NumArgsInPartiallySubstitutedPack == NumExplicitArgs) &&
2828          "Wrong number of arguments in partially-substituted pack");
2829   PartiallySubstitutedPack = Pack;
2830   ArgsInPartiallySubstitutedPack = ExplicitArgs;
2831   NumArgsInPartiallySubstitutedPack = NumExplicitArgs;
2832 }
2833 
2834 NamedDecl *LocalInstantiationScope::getPartiallySubstitutedPack(
2835                                          const TemplateArgument **ExplicitArgs,
2836                                               unsigned *NumExplicitArgs) const {
2837   if (ExplicitArgs)
2838     *ExplicitArgs = nullptr;
2839   if (NumExplicitArgs)
2840     *NumExplicitArgs = 0;
2841 
2842   for (const LocalInstantiationScope *Current = this; Current;
2843        Current = Current->Outer) {
2844     if (Current->PartiallySubstitutedPack) {
2845       if (ExplicitArgs)
2846         *ExplicitArgs = Current->ArgsInPartiallySubstitutedPack;
2847       if (NumExplicitArgs)
2848         *NumExplicitArgs = Current->NumArgsInPartiallySubstitutedPack;
2849 
2850       return Current->PartiallySubstitutedPack;
2851     }
2852 
2853     if (!Current->CombineWithOuterScope)
2854       break;
2855   }
2856 
2857   return nullptr;
2858 }
2859