1 //===-- lib/Semantics/resolve-labels.cpp ----------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
9 #include "resolve-labels.h"
10 #include "flang/Common/enum-set.h"
11 #include "flang/Common/template.h"
12 #include "flang/Parser/parse-tree-visitor.h"
13 #include "flang/Semantics/semantics.h"
14 #include <cctype>
15 #include <cstdarg>
16 #include <type_traits>
17 
18 namespace Fortran::semantics {
19 
20 using namespace parser::literals;
21 
22 ENUM_CLASS(
23     TargetStatementEnum, Do, Branch, Format, CompatibleDo, CompatibleBranch)
24 using LabeledStmtClassificationSet =
25     common::EnumSet<TargetStatementEnum, TargetStatementEnum_enumSize>;
26 
27 using IndexList = std::vector<std::pair<parser::CharBlock, parser::CharBlock>>;
28 // A ProxyForScope is an integral proxy for a Fortran scope. This is required
29 // because the parse tree does not actually have the scopes required.
30 using ProxyForScope = unsigned;
31 // Minimal scope information
32 struct ScopeInfo {
33   ProxyForScope parent{};
34   bool isExteriorGotoFatal{false};
35   int depth{0};
36 };
37 struct LabeledStatementInfoTuplePOD {
38   ProxyForScope proxyForScope;
39   parser::CharBlock parserCharBlock;
40   LabeledStmtClassificationSet labeledStmtClassificationSet;
41   bool isExecutableConstructEndStmt;
42 };
43 using TargetStmtMap = std::map<parser::Label, LabeledStatementInfoTuplePOD>;
44 struct SourceStatementInfoTuplePOD {
45   SourceStatementInfoTuplePOD(const parser::Label &parserLabel,
46       const ProxyForScope &proxyForScope,
47       const parser::CharBlock &parserCharBlock)
48       : parserLabel{parserLabel}, proxyForScope{proxyForScope},
49         parserCharBlock{parserCharBlock} {}
50   parser::Label parserLabel;
51   ProxyForScope proxyForScope;
52   parser::CharBlock parserCharBlock;
53 };
54 using SourceStmtList = std::vector<SourceStatementInfoTuplePOD>;
55 enum class Legality { never, always, formerly };
56 
57 bool HasScope(ProxyForScope scope) { return scope != ProxyForScope{0u}; }
58 
59 // F18:R1131
60 template <typename A>
61 constexpr Legality IsLegalDoTerm(const parser::Statement<A> &) {
62   if (std::is_same_v<A, common::Indirection<parser::EndDoStmt>> ||
63       std::is_same_v<A, parser::EndDoStmt>) {
64     return Legality::always;
65   } else if (std::is_same_v<A, parser::EndForallStmt> ||
66       std::is_same_v<A, parser::EndWhereStmt>) {
67     // Executable construct end statements are also supported as
68     // an extension but they need special care because the associated
69     // construct create their own scope.
70     return Legality::formerly;
71   } else {
72     return Legality::never;
73   }
74 }
75 
76 constexpr Legality IsLegalDoTerm(
77     const parser::Statement<parser::ActionStmt> &actionStmt) {
78   if (std::holds_alternative<parser::ContinueStmt>(actionStmt.statement.u)) {
79     // See F08:C816
80     return Legality::always;
81   } else if (!(std::holds_alternative<
82                    common::Indirection<parser::ArithmeticIfStmt>>(
83                    actionStmt.statement.u) ||
84                  std::holds_alternative<common::Indirection<parser::CycleStmt>>(
85                      actionStmt.statement.u) ||
86                  std::holds_alternative<common::Indirection<parser::ExitStmt>>(
87                      actionStmt.statement.u) ||
88                  std::holds_alternative<common::Indirection<parser::StopStmt>>(
89                      actionStmt.statement.u) ||
90                  std::holds_alternative<common::Indirection<parser::GotoStmt>>(
91                      actionStmt.statement.u) ||
92                  std::holds_alternative<
93                      common::Indirection<parser::ReturnStmt>>(
94                      actionStmt.statement.u))) {
95     return Legality::formerly;
96   } else {
97     return Legality::never;
98   }
99 }
100 
101 template <typename A> constexpr bool IsFormat(const parser::Statement<A> &) {
102   return std::is_same_v<A, common::Indirection<parser::FormatStmt>>;
103 }
104 
105 template <typename A>
106 constexpr Legality IsLegalBranchTarget(const parser::Statement<A> &) {
107   if (std::is_same_v<A, parser::ActionStmt> ||
108       std::is_same_v<A, parser::AssociateStmt> ||
109       std::is_same_v<A, parser::EndAssociateStmt> ||
110       std::is_same_v<A, parser::IfThenStmt> ||
111       std::is_same_v<A, parser::EndIfStmt> ||
112       std::is_same_v<A, parser::SelectCaseStmt> ||
113       std::is_same_v<A, parser::EndSelectStmt> ||
114       std::is_same_v<A, parser::SelectRankStmt> ||
115       std::is_same_v<A, parser::SelectTypeStmt> ||
116       std::is_same_v<A, common::Indirection<parser::LabelDoStmt>> ||
117       std::is_same_v<A, parser::NonLabelDoStmt> ||
118       std::is_same_v<A, parser::EndDoStmt> ||
119       std::is_same_v<A, common::Indirection<parser::EndDoStmt>> ||
120       std::is_same_v<A, parser::BlockStmt> ||
121       std::is_same_v<A, parser::EndBlockStmt> ||
122       std::is_same_v<A, parser::CriticalStmt> ||
123       std::is_same_v<A, parser::EndCriticalStmt> ||
124       std::is_same_v<A, parser::ForallConstructStmt> ||
125       std::is_same_v<A, parser::WhereConstructStmt> ||
126       std::is_same_v<A, parser::EndFunctionStmt> ||
127       std::is_same_v<A, parser::EndMpSubprogramStmt> ||
128       std::is_same_v<A, parser::EndProgramStmt> ||
129       std::is_same_v<A, parser::EndSubroutineStmt>) {
130     return Legality::always;
131   } else {
132     return Legality::never;
133   }
134 }
135 
136 template <typename A>
137 constexpr LabeledStmtClassificationSet ConstructBranchTargetFlags(
138     const parser::Statement<A> &statement) {
139   LabeledStmtClassificationSet labeledStmtClassificationSet{};
140   if (IsLegalDoTerm(statement) == Legality::always) {
141     labeledStmtClassificationSet.set(TargetStatementEnum::Do);
142   } else if (IsLegalDoTerm(statement) == Legality::formerly) {
143     labeledStmtClassificationSet.set(TargetStatementEnum::CompatibleDo);
144   }
145   if (IsLegalBranchTarget(statement) == Legality::always) {
146     labeledStmtClassificationSet.set(TargetStatementEnum::Branch);
147   } else if (IsLegalBranchTarget(statement) == Legality::formerly) {
148     labeledStmtClassificationSet.set(TargetStatementEnum::CompatibleBranch);
149   }
150   if (IsFormat(statement)) {
151     labeledStmtClassificationSet.set(TargetStatementEnum::Format);
152   }
153   return labeledStmtClassificationSet;
154 }
155 
156 static unsigned SayLabel(parser::Label label) {
157   return static_cast<unsigned>(label);
158 }
159 
160 struct UnitAnalysis {
161   UnitAnalysis() { scopeModel.emplace_back(); }
162 
163   SourceStmtList doStmtSources;
164   SourceStmtList formatStmtSources;
165   SourceStmtList otherStmtSources;
166   SourceStmtList assignStmtSources;
167   TargetStmtMap targetStmts;
168   std::vector<ScopeInfo> scopeModel;
169 };
170 
171 // Some parse tree record for statements simply wrap construct names;
172 // others include them as tuple components.  Given a statement,
173 // return a pointer to its name if it has one.
174 template <typename A>
175 const parser::CharBlock *GetStmtName(const parser::Statement<A> &stmt) {
176   const std::optional<parser::Name> *name{nullptr};
177   if constexpr (WrapperTrait<A>) {
178     if constexpr (std::is_same_v<decltype(A::v), parser::Name>) {
179       return &stmt.statement.v.source;
180     } else {
181       name = &stmt.statement.v;
182     }
183   } else if constexpr (std::is_same_v<A, parser::SelectRankStmt> ||
184       std::is_same_v<A, parser::SelectTypeStmt>) {
185     name = &std::get<0>(stmt.statement.t);
186   } else if constexpr (common::HasMember<parser::Name,
187                            decltype(stmt.statement.t)>) {
188     return &std::get<parser::Name>(stmt.statement.t).source;
189   } else {
190     name = &std::get<std::optional<parser::Name>>(stmt.statement.t);
191   }
192   if (name && *name) {
193     return &(*name)->source;
194   }
195   return nullptr;
196 }
197 
198 class ParseTreeAnalyzer {
199 public:
200   ParseTreeAnalyzer(ParseTreeAnalyzer &&that) = default;
201   ParseTreeAnalyzer(SemanticsContext &context) : context_{context} {}
202 
203   template <typename A> constexpr bool Pre(const A &x) {
204     using LabeledProgramUnitStmts =
205         std::tuple<parser::MainProgram, parser::FunctionSubprogram,
206             parser::SubroutineSubprogram, parser::SeparateModuleSubprogram>;
207     if constexpr (common::HasMember<A, LabeledProgramUnitStmts>) {
208       const auto &endStmt{std::get<std::tuple_size_v<decltype(x.t)> - 1>(x.t)};
209       if (endStmt.label) {
210         // The END statement for a subprogram appears after any internal
211         // subprograms.  Visit that statement in advance so that results
212         // are placed in the correct programUnits_ slot.
213         auto targetFlags{ConstructBranchTargetFlags(endStmt)};
214         AddTargetLabelDefinition(
215             endStmt.label.value(), targetFlags, currentScope_);
216       }
217     }
218     return true;
219   }
220   template <typename A> constexpr void Post(const A &) {}
221 
222   template <typename A> bool Pre(const parser::Statement<A> &statement) {
223     currentPosition_ = statement.source;
224     const auto &label = statement.label;
225     if (!label) {
226       return true;
227     }
228     using LabeledConstructStmts = std::tuple<parser::AssociateStmt,
229         parser::BlockStmt, parser::ChangeTeamStmt, parser::CriticalStmt,
230         parser::IfThenStmt, parser::NonLabelDoStmt, parser::SelectCaseStmt,
231         parser::SelectRankStmt, parser::SelectTypeStmt,
232         parser::ForallConstructStmt, parser::WhereConstructStmt>;
233     using LabeledConstructEndStmts = std::tuple<parser::EndAssociateStmt,
234         parser::EndBlockStmt, parser::EndChangeTeamStmt,
235         parser::EndCriticalStmt, parser::EndDoStmt, parser::EndForallStmt,
236         parser::EndIfStmt, parser::EndSelectStmt, parser::EndWhereStmt>;
237     using LabeledProgramUnitEndStmts =
238         std::tuple<parser::EndFunctionStmt, parser::EndMpSubprogramStmt,
239             parser::EndProgramStmt, parser::EndSubroutineStmt>;
240     auto targetFlags{ConstructBranchTargetFlags(statement)};
241     if constexpr (common::HasMember<A, LabeledConstructStmts>) {
242       AddTargetLabelDefinition(label.value(), targetFlags, ParentScope());
243     } else if constexpr (common::HasMember<A, LabeledConstructEndStmts>) {
244       constexpr bool isExecutableConstructEndStmt{true};
245       AddTargetLabelDefinition(label.value(), targetFlags, currentScope_,
246           isExecutableConstructEndStmt);
247     } else if constexpr (!common::HasMember<A, LabeledProgramUnitEndStmts>) {
248       // Program unit END statements have already been processed.
249       AddTargetLabelDefinition(label.value(), targetFlags, currentScope_);
250     }
251     return true;
252   }
253 
254   // see 11.1.1
255   bool Pre(const parser::ProgramUnit &) { return InitializeNewScopeContext(); }
256   bool Pre(const parser::InternalSubprogram &) {
257     return InitializeNewScopeContext();
258   }
259   bool Pre(const parser::ModuleSubprogram &) {
260     return InitializeNewScopeContext();
261   }
262   bool Pre(const parser::AssociateConstruct &associateConstruct) {
263     return PushConstructName(associateConstruct);
264   }
265   bool Pre(const parser::BlockConstruct &blockConstruct) {
266     return PushConstructName(blockConstruct);
267   }
268   bool Pre(const parser::ChangeTeamConstruct &changeTeamConstruct) {
269     return PushConstructName(changeTeamConstruct);
270   }
271   bool Pre(const parser::CriticalConstruct &criticalConstruct) {
272     return PushConstructName(criticalConstruct);
273   }
274   bool Pre(const parser::DoConstruct &doConstruct) {
275     return PushConstructName(doConstruct);
276   }
277   bool Pre(const parser::IfConstruct &ifConstruct) {
278     return PushConstructName(ifConstruct);
279   }
280   bool Pre(const parser::IfConstruct::ElseIfBlock &) {
281     return SwitchToNewScope();
282   }
283   bool Pre(const parser::IfConstruct::ElseBlock &) {
284     return SwitchToNewScope();
285   }
286   bool Pre(const parser::CaseConstruct &caseConstruct) {
287     return PushConstructName(caseConstruct);
288   }
289   bool Pre(const parser::CaseConstruct::Case &) { return SwitchToNewScope(); }
290   bool Pre(const parser::SelectRankConstruct &selectRankConstruct) {
291     return PushConstructName(selectRankConstruct);
292   }
293   bool Pre(const parser::SelectRankConstruct::RankCase &) {
294     return SwitchToNewScope();
295   }
296   bool Pre(const parser::SelectTypeConstruct &selectTypeConstruct) {
297     return PushConstructName(selectTypeConstruct);
298   }
299   bool Pre(const parser::SelectTypeConstruct::TypeCase &) {
300     return SwitchToNewScope();
301   }
302   bool Pre(const parser::WhereConstruct &whereConstruct) {
303     return PushConstructName(whereConstruct);
304   }
305   bool Pre(const parser::ForallConstruct &forallConstruct) {
306     return PushConstructName(forallConstruct);
307   }
308 
309   void Post(const parser::AssociateConstruct &associateConstruct) {
310     PopConstructName(associateConstruct);
311   }
312   void Post(const parser::BlockConstruct &blockConstruct) {
313     PopConstructName(blockConstruct);
314   }
315   void Post(const parser::ChangeTeamConstruct &changeTeamConstruct) {
316     PopConstructName(changeTeamConstruct);
317   }
318   void Post(const parser::CriticalConstruct &criticalConstruct) {
319     PopConstructName(criticalConstruct);
320   }
321   void Post(const parser::DoConstruct &doConstruct) {
322     PopConstructName(doConstruct);
323   }
324   void Post(const parser::IfConstruct &ifConstruct) {
325     PopConstructName(ifConstruct);
326   }
327   void Post(const parser::CaseConstruct &caseConstruct) {
328     PopConstructName(caseConstruct);
329   }
330   void Post(const parser::SelectRankConstruct &selectRankConstruct) {
331     PopConstructName(selectRankConstruct);
332   }
333   void Post(const parser::SelectTypeConstruct &selectTypeConstruct) {
334     PopConstructName(selectTypeConstruct);
335   }
336   void Post(const parser::WhereConstruct &whereConstruct) {
337     PopConstructName(whereConstruct);
338   }
339   void Post(const parser::ForallConstruct &forallConstruct) {
340     PopConstructName(forallConstruct);
341   }
342 
343   // Checks for missing or mismatching names on various constructs (e.g., IF)
344   // and their intermediate or terminal statements that allow optional
345   // construct names(e.g., ELSE).  When an optional construct name is present,
346   // the construct as a whole must have a name that matches.
347   template <typename FIRST, typename CONSTRUCT, typename STMT>
348   void CheckOptionalName(const char *constructTag, const CONSTRUCT &a,
349       const parser::Statement<STMT> &stmt) {
350     if (const parser::CharBlock * name{GetStmtName(stmt)}) {
351       const auto &firstStmt{std::get<parser::Statement<FIRST>>(a.t)};
352       if (const parser::CharBlock * firstName{GetStmtName(firstStmt)}) {
353         if (*firstName != *name) {
354           context_.Say(*name, "%s name mismatch"_err_en_US, constructTag)
355               .Attach(*firstName, "should be"_en_US);
356         }
357       } else {
358         context_.Say(*name, "%s name not allowed"_err_en_US, constructTag)
359             .Attach(firstStmt.source, "in unnamed %s"_en_US, constructTag);
360       }
361     }
362   }
363 
364   // C1414
365   void Post(const parser::BlockData &blockData) {
366     CheckOptionalName<parser::BlockDataStmt>("BLOCK DATA subprogram", blockData,
367         std::get<parser::Statement<parser::EndBlockDataStmt>>(blockData.t));
368   }
369 
370   // C1564
371   void Post(const parser::InterfaceBody::Function &func) {
372     CheckOptionalName<parser::FunctionStmt>("FUNCTION", func,
373         std::get<parser::Statement<parser::EndFunctionStmt>>(func.t));
374   }
375 
376   // C1564
377   void Post(const parser::FunctionSubprogram &functionSubprogram) {
378     CheckOptionalName<parser::FunctionStmt>("FUNCTION", functionSubprogram,
379         std::get<parser::Statement<parser::EndFunctionStmt>>(
380             functionSubprogram.t));
381   }
382 
383   // C1502
384   void Post(const parser::InterfaceBlock &interfaceBlock) {
385     if (const auto &endGenericSpec{
386             std::get<parser::Statement<parser::EndInterfaceStmt>>(
387                 interfaceBlock.t)
388                 .statement.v}) {
389       const auto &interfaceStmt{
390           std::get<parser::Statement<parser::InterfaceStmt>>(interfaceBlock.t)};
391       if (std::holds_alternative<parser::Abstract>(interfaceStmt.statement.u)) {
392         context_
393             .Say(endGenericSpec->source,
394                 "END INTERFACE generic name (%s) may not appear for ABSTRACT INTERFACE"_err_en_US,
395                 endGenericSpec->source)
396             .Attach(
397                 interfaceStmt.source, "corresponding ABSTRACT INTERFACE"_en_US);
398       } else if (const auto &genericSpec{
399                      std::get<std::optional<parser::GenericSpec>>(
400                          interfaceStmt.statement.u)}) {
401         bool ok{genericSpec->source == endGenericSpec->source};
402         if (!ok) {
403           // Accept variant spellings of .LT. &c.
404           const auto *endOp{
405               std::get_if<parser::DefinedOperator>(&endGenericSpec->u)};
406           const auto *op{std::get_if<parser::DefinedOperator>(&genericSpec->u)};
407           if (endOp && op) {
408             const auto *endIntrin{
409                 std::get_if<parser::DefinedOperator::IntrinsicOperator>(
410                     &endOp->u)};
411             const auto *intrin{
412                 std::get_if<parser::DefinedOperator::IntrinsicOperator>(
413                     &op->u)};
414             ok = endIntrin && intrin && *endIntrin == *intrin;
415           }
416         }
417         if (!ok) {
418           context_
419               .Say(endGenericSpec->source,
420                   "END INTERFACE generic name (%s) does not match generic INTERFACE (%s)"_err_en_US,
421                   endGenericSpec->source, genericSpec->source)
422               .Attach(genericSpec->source, "corresponding INTERFACE"_en_US);
423         }
424       } else {
425         context_
426             .Say(endGenericSpec->source,
427                 "END INTERFACE generic name (%s) may not appear for non-generic INTERFACE"_err_en_US,
428                 endGenericSpec->source)
429             .Attach(interfaceStmt.source, "corresponding INTERFACE"_en_US);
430       }
431     }
432   }
433 
434   // C1402
435   void Post(const parser::Module &module) {
436     CheckOptionalName<parser::ModuleStmt>("MODULE", module,
437         std::get<parser::Statement<parser::EndModuleStmt>>(module.t));
438   }
439 
440   // C1569
441   void Post(const parser::SeparateModuleSubprogram &separateModuleSubprogram) {
442     CheckOptionalName<parser::MpSubprogramStmt>("MODULE PROCEDURE",
443         separateModuleSubprogram,
444         std::get<parser::Statement<parser::EndMpSubprogramStmt>>(
445             separateModuleSubprogram.t));
446   }
447 
448   // C1401
449   void Post(const parser::MainProgram &mainProgram) {
450     if (const parser::CharBlock *
451         endName{GetStmtName(std::get<parser::Statement<parser::EndProgramStmt>>(
452             mainProgram.t))}) {
453       if (const auto &program{
454               std::get<std::optional<parser::Statement<parser::ProgramStmt>>>(
455                   mainProgram.t)}) {
456         if (*endName != program->statement.v.source) {
457           context_.Say(*endName, "END PROGRAM name mismatch"_err_en_US)
458               .Attach(program->statement.v.source, "should be"_en_US);
459         }
460       } else {
461         context_.Say(*endName,
462             "END PROGRAM has name without PROGRAM statement"_err_en_US);
463       }
464     }
465   }
466 
467   // C1413
468   void Post(const parser::Submodule &submodule) {
469     CheckOptionalName<parser::SubmoduleStmt>("SUBMODULE", submodule,
470         std::get<parser::Statement<parser::EndSubmoduleStmt>>(submodule.t));
471   }
472 
473   // C1567
474   void Post(const parser::InterfaceBody::Subroutine &sub) {
475     CheckOptionalName<parser::SubroutineStmt>("SUBROUTINE", sub,
476         std::get<parser::Statement<parser::EndSubroutineStmt>>(sub.t));
477   }
478 
479   // C1567
480   void Post(const parser::SubroutineSubprogram &subroutineSubprogram) {
481     CheckOptionalName<parser::SubroutineStmt>("SUBROUTINE",
482         subroutineSubprogram,
483         std::get<parser::Statement<parser::EndSubroutineStmt>>(
484             subroutineSubprogram.t));
485   }
486 
487   // C739
488   void Post(const parser::DerivedTypeDef &derivedTypeDef) {
489     CheckOptionalName<parser::DerivedTypeStmt>("derived type definition",
490         derivedTypeDef,
491         std::get<parser::Statement<parser::EndTypeStmt>>(derivedTypeDef.t));
492   }
493 
494   void Post(const parser::LabelDoStmt &labelDoStmt) {
495     AddLabelReferenceFromDoStmt(std::get<parser::Label>(labelDoStmt.t));
496   }
497   void Post(const parser::GotoStmt &gotoStmt) { AddLabelReference(gotoStmt.v); }
498   void Post(const parser::ComputedGotoStmt &computedGotoStmt) {
499     AddLabelReference(std::get<std::list<parser::Label>>(computedGotoStmt.t));
500   }
501   void Post(const parser::ArithmeticIfStmt &arithmeticIfStmt) {
502     AddLabelReference(std::get<1>(arithmeticIfStmt.t));
503     AddLabelReference(std::get<2>(arithmeticIfStmt.t));
504     AddLabelReference(std::get<3>(arithmeticIfStmt.t));
505   }
506   void Post(const parser::AssignStmt &assignStmt) {
507     AddLabelReferenceFromAssignStmt(std::get<parser::Label>(assignStmt.t));
508   }
509   void Post(const parser::AssignedGotoStmt &assignedGotoStmt) {
510     AddLabelReference(std::get<std::list<parser::Label>>(assignedGotoStmt.t));
511   }
512   void Post(const parser::AltReturnSpec &altReturnSpec) {
513     AddLabelReference(altReturnSpec.v);
514   }
515 
516   void Post(const parser::ErrLabel &errLabel) { AddLabelReference(errLabel.v); }
517   void Post(const parser::EndLabel &endLabel) { AddLabelReference(endLabel.v); }
518   void Post(const parser::EorLabel &eorLabel) { AddLabelReference(eorLabel.v); }
519   void Post(const parser::Format &format) {
520     if (const auto *labelPointer{std::get_if<parser::Label>(&format.u)}) {
521       AddLabelReferenceToFormatStmt(*labelPointer);
522     }
523   }
524   void Post(const parser::CycleStmt &cycleStmt) {
525     if (cycleStmt.v) {
526       CheckLabelContext("CYCLE", cycleStmt.v->source);
527     }
528   }
529   void Post(const parser::ExitStmt &exitStmt) {
530     if (exitStmt.v) {
531       CheckLabelContext("EXIT", exitStmt.v->source);
532     }
533   }
534 
535   const std::vector<UnitAnalysis> &ProgramUnits() const {
536     return programUnits_;
537   }
538   SemanticsContext &ErrorHandler() { return context_; }
539 
540 private:
541   ScopeInfo &PushScope() {
542     auto &model{programUnits_.back().scopeModel};
543     int newDepth{model.empty() ? 1 : model[currentScope_].depth + 1};
544     ScopeInfo &result{model.emplace_back()};
545     result.parent = currentScope_;
546     result.depth = newDepth;
547     currentScope_ = model.size() - 1;
548     return result;
549   }
550   bool InitializeNewScopeContext() {
551     programUnits_.emplace_back(UnitAnalysis{});
552     currentScope_ = 0u;
553     PushScope();
554     return true;
555   }
556   ScopeInfo &PopScope() {
557     ScopeInfo &result{programUnits_.back().scopeModel[currentScope_]};
558     currentScope_ = result.parent;
559     return result;
560   }
561   ProxyForScope ParentScope() {
562     return programUnits_.back().scopeModel[currentScope_].parent;
563   }
564   bool SwitchToNewScope() {
565     ScopeInfo &oldScope{PopScope()};
566     bool isExteriorGotoFatal{oldScope.isExteriorGotoFatal};
567     PushScope().isExteriorGotoFatal = isExteriorGotoFatal;
568     return true;
569   }
570 
571   template <typename A> bool PushConstructName(const A &a) {
572     const auto &optionalName{std::get<0>(std::get<0>(a.t).statement.t)};
573     if (optionalName) {
574       constructNames_.emplace_back(optionalName->ToString());
575     }
576     // Gotos into this construct from outside it are diagnosed, and
577     // are fatal unless the construct is a DO, IF, or SELECT CASE.
578     PushScope().isExteriorGotoFatal =
579         !(std::is_same_v<A, parser::DoConstruct> ||
580             std::is_same_v<A, parser::IfConstruct> ||
581             std::is_same_v<A, parser::CaseConstruct>);
582     return true;
583   }
584   bool PushConstructName(const parser::BlockConstruct &blockConstruct) {
585     const auto &optionalName{
586         std::get<parser::Statement<parser::BlockStmt>>(blockConstruct.t)
587             .statement.v};
588     if (optionalName) {
589       constructNames_.emplace_back(optionalName->ToString());
590     }
591     PushScope().isExteriorGotoFatal = true;
592     return true;
593   }
594   template <typename A> void PopConstructNameIfPresent(const A &a) {
595     const auto &optionalName{std::get<0>(std::get<0>(a.t).statement.t)};
596     if (optionalName) {
597       constructNames_.pop_back();
598     }
599   }
600   void PopConstructNameIfPresent(const parser::BlockConstruct &blockConstruct) {
601     const auto &optionalName{
602         std::get<parser::Statement<parser::BlockStmt>>(blockConstruct.t)
603             .statement.v};
604     if (optionalName) {
605       constructNames_.pop_back();
606     }
607   }
608 
609   template <typename A> void PopConstructName(const A &a) {
610     CheckName(a);
611     PopScope();
612     PopConstructNameIfPresent(a);
613   }
614 
615   template <typename FIRST, typename CASEBLOCK, typename CASE,
616       typename CONSTRUCT>
617   void CheckSelectNames(const char *tag, const CONSTRUCT &construct) {
618     CheckEndName<FIRST, parser::EndSelectStmt>(tag, construct);
619     for (const auto &inner : std::get<std::list<CASEBLOCK>>(construct.t)) {
620       CheckOptionalName<FIRST>(
621           tag, construct, std::get<parser::Statement<CASE>>(inner.t));
622     }
623   }
624 
625   // C1144
626   void PopConstructName(const parser::CaseConstruct &caseConstruct) {
627     CheckSelectNames<parser::SelectCaseStmt, parser::CaseConstruct::Case,
628         parser::CaseStmt>("SELECT CASE", caseConstruct);
629     PopScope();
630     PopConstructNameIfPresent(caseConstruct);
631   }
632 
633   // C1154, C1156
634   void PopConstructName(
635       const parser::SelectRankConstruct &selectRankConstruct) {
636     CheckSelectNames<parser::SelectRankStmt,
637         parser::SelectRankConstruct::RankCase, parser::SelectRankCaseStmt>(
638         "SELECT RANK", selectRankConstruct);
639     PopScope();
640     PopConstructNameIfPresent(selectRankConstruct);
641   }
642 
643   // C1165
644   void PopConstructName(
645       const parser::SelectTypeConstruct &selectTypeConstruct) {
646     CheckSelectNames<parser::SelectTypeStmt,
647         parser::SelectTypeConstruct::TypeCase, parser::TypeGuardStmt>(
648         "SELECT TYPE", selectTypeConstruct);
649     PopScope();
650     PopConstructNameIfPresent(selectTypeConstruct);
651   }
652 
653   // Checks for missing or mismatching names on various constructs (e.g., BLOCK)
654   // and their END statements.  Both names must be present if either one is.
655   template <typename FIRST, typename END, typename CONSTRUCT>
656   void CheckEndName(const char *constructTag, const CONSTRUCT &a) {
657     const auto &constructStmt{std::get<parser::Statement<FIRST>>(a.t)};
658     const auto &endStmt{std::get<parser::Statement<END>>(a.t)};
659     const parser::CharBlock *endName{GetStmtName(endStmt)};
660     if (const parser::CharBlock * constructName{GetStmtName(constructStmt)}) {
661       if (endName) {
662         if (*constructName != *endName) {
663           context_
664               .Say(*endName, "%s construct name mismatch"_err_en_US,
665                   constructTag)
666               .Attach(*constructName, "should be"_en_US);
667         }
668       } else {
669         context_
670             .Say(endStmt.source,
671                 "%s construct name required but missing"_err_en_US,
672                 constructTag)
673             .Attach(*constructName, "should be"_en_US);
674       }
675     } else if (endName) {
676       context_
677           .Say(*endName, "%s construct name unexpected"_err_en_US, constructTag)
678           .Attach(
679               constructStmt.source, "unnamed %s statement"_en_US, constructTag);
680     }
681   }
682 
683   // C1106
684   void CheckName(const parser::AssociateConstruct &associateConstruct) {
685     CheckEndName<parser::AssociateStmt, parser::EndAssociateStmt>(
686         "ASSOCIATE", associateConstruct);
687   }
688   // C1117
689   void CheckName(const parser::CriticalConstruct &criticalConstruct) {
690     CheckEndName<parser::CriticalStmt, parser::EndCriticalStmt>(
691         "CRITICAL", criticalConstruct);
692   }
693   // C1131
694   void CheckName(const parser::DoConstruct &doConstruct) {
695     CheckEndName<parser::NonLabelDoStmt, parser::EndDoStmt>("DO", doConstruct);
696   }
697   // C1035
698   void CheckName(const parser::ForallConstruct &forallConstruct) {
699     CheckEndName<parser::ForallConstructStmt, parser::EndForallStmt>(
700         "FORALL", forallConstruct);
701   }
702 
703   // C1109
704   void CheckName(const parser::BlockConstruct &blockConstruct) {
705     CheckEndName<parser::BlockStmt, parser::EndBlockStmt>(
706         "BLOCK", blockConstruct);
707   }
708   // C1112
709   void CheckName(const parser::ChangeTeamConstruct &changeTeamConstruct) {
710     CheckEndName<parser::ChangeTeamStmt, parser::EndChangeTeamStmt>(
711         "CHANGE TEAM", changeTeamConstruct);
712   }
713 
714   // C1142
715   void CheckName(const parser::IfConstruct &ifConstruct) {
716     CheckEndName<parser::IfThenStmt, parser::EndIfStmt>("IF", ifConstruct);
717     for (const auto &elseIfBlock :
718         std::get<std::list<parser::IfConstruct::ElseIfBlock>>(ifConstruct.t)) {
719       CheckOptionalName<parser::IfThenStmt>("IF construct", ifConstruct,
720           std::get<parser::Statement<parser::ElseIfStmt>>(elseIfBlock.t));
721     }
722     if (const auto &elseBlock{
723             std::get<std::optional<parser::IfConstruct::ElseBlock>>(
724                 ifConstruct.t)}) {
725       CheckOptionalName<parser::IfThenStmt>("IF construct", ifConstruct,
726           std::get<parser::Statement<parser::ElseStmt>>(elseBlock->t));
727     }
728   }
729 
730   // C1033
731   void CheckName(const parser::WhereConstruct &whereConstruct) {
732     CheckEndName<parser::WhereConstructStmt, parser::EndWhereStmt>(
733         "WHERE", whereConstruct);
734     for (const auto &maskedElsewhere :
735         std::get<std::list<parser::WhereConstruct::MaskedElsewhere>>(
736             whereConstruct.t)) {
737       CheckOptionalName<parser::WhereConstructStmt>("WHERE construct",
738           whereConstruct,
739           std::get<parser::Statement<parser::MaskedElsewhereStmt>>(
740               maskedElsewhere.t));
741     }
742     if (const auto &elsewhere{
743             std::get<std::optional<parser::WhereConstruct::Elsewhere>>(
744                 whereConstruct.t)}) {
745       CheckOptionalName<parser::WhereConstructStmt>("WHERE construct",
746           whereConstruct,
747           std::get<parser::Statement<parser::ElsewhereStmt>>(elsewhere->t));
748     }
749   }
750 
751   // C1134, C1166
752   void CheckLabelContext(
753       const char *const stmtString, const parser::CharBlock &constructName) {
754     const auto iter{std::find(constructNames_.crbegin(),
755         constructNames_.crend(), constructName.ToString())};
756     if (iter == constructNames_.crend()) {
757       context_.Say(constructName, "%s construct-name is not in scope"_err_en_US,
758           stmtString);
759     }
760   }
761 
762   // 6.2.5, paragraph 2
763   void CheckLabelInRange(parser::Label label) {
764     if (label < 1 || label > 99999) {
765       context_.Say(currentPosition_, "Label '%u' is out of range"_err_en_US,
766           SayLabel(label));
767     }
768   }
769 
770   // 6.2.5., paragraph 2
771   void AddTargetLabelDefinition(parser::Label label,
772       LabeledStmtClassificationSet labeledStmtClassificationSet,
773       ProxyForScope scope, bool isExecutableConstructEndStmt = false) {
774     CheckLabelInRange(label);
775     const auto pair{programUnits_.back().targetStmts.emplace(label,
776         LabeledStatementInfoTuplePOD{scope, currentPosition_,
777             labeledStmtClassificationSet, isExecutableConstructEndStmt})};
778     if (!pair.second) {
779       context_.Say(currentPosition_, "Label '%u' is not distinct"_err_en_US,
780           SayLabel(label));
781     }
782   }
783 
784   void AddLabelReferenceFromDoStmt(parser::Label label) {
785     CheckLabelInRange(label);
786     programUnits_.back().doStmtSources.emplace_back(
787         label, currentScope_, currentPosition_);
788   }
789 
790   void AddLabelReferenceToFormatStmt(parser::Label label) {
791     CheckLabelInRange(label);
792     programUnits_.back().formatStmtSources.emplace_back(
793         label, currentScope_, currentPosition_);
794   }
795 
796   void AddLabelReferenceFromAssignStmt(parser::Label label) {
797     CheckLabelInRange(label);
798     programUnits_.back().assignStmtSources.emplace_back(
799         label, currentScope_, currentPosition_);
800   }
801 
802   void AddLabelReference(parser::Label label) {
803     CheckLabelInRange(label);
804     programUnits_.back().otherStmtSources.emplace_back(
805         label, currentScope_, currentPosition_);
806   }
807 
808   void AddLabelReference(const std::list<parser::Label> &labels) {
809     for (const parser::Label &label : labels) {
810       AddLabelReference(label);
811     }
812   }
813 
814   std::vector<UnitAnalysis> programUnits_;
815   SemanticsContext &context_;
816   parser::CharBlock currentPosition_;
817   ProxyForScope currentScope_;
818   std::vector<std::string> constructNames_;
819 };
820 
821 bool InInclusiveScope(const std::vector<ScopeInfo> &scopes, ProxyForScope tail,
822     ProxyForScope head) {
823   for (; tail != head; tail = scopes[tail].parent) {
824     if (!HasScope(tail)) {
825       return false;
826     }
827   }
828   return true;
829 }
830 
831 ParseTreeAnalyzer LabelAnalysis(
832     SemanticsContext &context, const parser::Program &program) {
833   ParseTreeAnalyzer analysis{context};
834   Walk(program, analysis);
835   return analysis;
836 }
837 
838 bool InBody(const parser::CharBlock &position,
839     const std::pair<parser::CharBlock, parser::CharBlock> &pair) {
840   if (position.begin() >= pair.first.begin()) {
841     if (position.begin() < pair.second.end()) {
842       return true;
843     }
844   }
845   return false;
846 }
847 
848 LabeledStatementInfoTuplePOD GetLabel(
849     const TargetStmtMap &labels, const parser::Label &label) {
850   const auto iter{labels.find(label)};
851   if (iter == labels.cend()) {
852     return {0u, nullptr, LabeledStmtClassificationSet{}, false};
853   } else {
854     return iter->second;
855   }
856 }
857 
858 // 11.1.7.3
859 void CheckBranchesIntoDoBody(const SourceStmtList &branches,
860     const TargetStmtMap &labels, const IndexList &loopBodies,
861     SemanticsContext &context) {
862   for (const auto &branch : branches) {
863     const auto &label{branch.parserLabel};
864     auto branchTarget{GetLabel(labels, label)};
865     if (HasScope(branchTarget.proxyForScope)) {
866       const auto &fromPosition{branch.parserCharBlock};
867       const auto &toPosition{branchTarget.parserCharBlock};
868       for (const auto &body : loopBodies) {
869         if (!InBody(fromPosition, body) && InBody(toPosition, body)) {
870           context
871               .Say(
872                   fromPosition, "branch into loop body from outside"_warn_en_US)
873               .Attach(body.first, "the loop branched into"_en_US);
874         }
875       }
876     }
877   }
878 }
879 
880 void CheckDoNesting(const IndexList &loopBodies, SemanticsContext &context) {
881   for (auto i1{loopBodies.cbegin()}; i1 != loopBodies.cend(); ++i1) {
882     const auto &v1{*i1};
883     for (auto i2{i1 + 1}; i2 != loopBodies.cend(); ++i2) {
884       const auto &v2{*i2};
885       if (v2.first.begin() < v1.second.end() &&
886           v1.second.begin() < v2.second.begin()) {
887         context.Say(v1.first, "DO loop doesn't properly nest"_err_en_US)
888             .Attach(v2.first, "DO loop conflicts"_en_US);
889       }
890     }
891   }
892 }
893 
894 parser::CharBlock SkipLabel(const parser::CharBlock &position) {
895   const std::size_t maxPosition{position.size()};
896   if (maxPosition && parser::IsDecimalDigit(position[0])) {
897     std::size_t i{1l};
898     for (; (i < maxPosition) && parser::IsDecimalDigit(position[i]); ++i) {
899     }
900     for (; (i < maxPosition) && std::isspace(position[i]); ++i) {
901     }
902     return parser::CharBlock{position.begin() + i, position.end()};
903   }
904   return position;
905 }
906 
907 ProxyForScope ParentScope(
908     const std::vector<ScopeInfo> &scopes, ProxyForScope scope) {
909   return scopes[scope].parent;
910 }
911 
912 void CheckLabelDoConstraints(const SourceStmtList &dos,
913     const SourceStmtList &branches, const TargetStmtMap &labels,
914     const std::vector<ScopeInfo> &scopes, SemanticsContext &context) {
915   IndexList loopBodies;
916   for (const auto &stmt : dos) {
917     const auto &label{stmt.parserLabel};
918     const auto &scope{stmt.proxyForScope};
919     const auto &position{stmt.parserCharBlock};
920     auto doTarget{GetLabel(labels, label)};
921     if (!HasScope(doTarget.proxyForScope)) {
922       // C1133
923       context.Say(
924           position, "Label '%u' cannot be found"_err_en_US, SayLabel(label));
925     } else if (doTarget.parserCharBlock.begin() < position.begin()) {
926       // R1119
927       context.Say(position,
928           "Label '%u' doesn't lexically follow DO stmt"_err_en_US,
929           SayLabel(label));
930 
931     } else if ((InInclusiveScope(scopes, scope, doTarget.proxyForScope) &&
932                    doTarget.labeledStmtClassificationSet.test(
933                        TargetStatementEnum::CompatibleDo)) ||
934         (doTarget.isExecutableConstructEndStmt &&
935             ParentScope(scopes, doTarget.proxyForScope) == scope)) {
936       if (context.warnOnNonstandardUsage() ||
937           context.ShouldWarn(
938               common::LanguageFeature::OldLabelDoEndStatements)) {
939         context
940             .Say(position,
941                 "A DO loop should terminate with an END DO or CONTINUE"_port_en_US)
942             .Attach(doTarget.parserCharBlock,
943                 "DO loop currently ends at statement:"_en_US);
944       }
945     } else if (!InInclusiveScope(scopes, scope, doTarget.proxyForScope)) {
946       context.Say(position, "Label '%u' is not in DO loop scope"_err_en_US,
947           SayLabel(label));
948     } else if (!doTarget.labeledStmtClassificationSet.test(
949                    TargetStatementEnum::Do)) {
950       context.Say(doTarget.parserCharBlock,
951           "A DO loop should terminate with an END DO or CONTINUE"_err_en_US);
952     } else {
953       loopBodies.emplace_back(SkipLabel(position), doTarget.parserCharBlock);
954     }
955   }
956 
957   CheckBranchesIntoDoBody(branches, labels, loopBodies, context);
958   CheckDoNesting(loopBodies, context);
959 }
960 
961 // 6.2.5
962 void CheckScopeConstraints(const SourceStmtList &stmts,
963     const TargetStmtMap &labels, const std::vector<ScopeInfo> &scopes,
964     SemanticsContext &context) {
965   for (const auto &stmt : stmts) {
966     const auto &label{stmt.parserLabel};
967     const auto &scope{stmt.proxyForScope};
968     const auto &position{stmt.parserCharBlock};
969     auto target{GetLabel(labels, label)};
970     if (!HasScope(target.proxyForScope)) {
971       context.Say(
972           position, "Label '%u' was not found"_err_en_US, SayLabel(label));
973     } else if (!InInclusiveScope(scopes, scope, target.proxyForScope)) {
974       // Clause 11.1.2.1 prohibits transfer of control to the interior of a
975       // block from outside the block, but this does not apply to formats.
976       // C1038 and C1034 forbid statements in FORALL and WHERE constructs
977       // (resp.) from being branch targets.
978       if (target.labeledStmtClassificationSet.test(
979               TargetStatementEnum::Format)) {
980         continue;
981       }
982       bool isFatal{false};
983       ProxyForScope fromScope{scope};
984       for (ProxyForScope toScope{target.proxyForScope}; fromScope != toScope;
985            toScope = scopes[toScope].parent) {
986         if (scopes[toScope].isExteriorGotoFatal) {
987           isFatal = true;
988           break;
989         }
990         if (scopes[toScope].depth == scopes[fromScope].depth) {
991           fromScope = scopes[fromScope].parent;
992         }
993       }
994       context.Say(position,
995           isFatal
996               ? "Label '%u' is in a construct that prevents its use as a branch target here"_err_en_US
997               : "Label '%u' is in a construct that prevents its use as a branch target here"_en_US,
998           SayLabel(label));
999     }
1000   }
1001 }
1002 
1003 void CheckBranchTargetConstraints(const SourceStmtList &stmts,
1004     const TargetStmtMap &labels, SemanticsContext &context) {
1005   for (const auto &stmt : stmts) {
1006     const auto &label{stmt.parserLabel};
1007     auto branchTarget{GetLabel(labels, label)};
1008     if (HasScope(branchTarget.proxyForScope)) {
1009       if (!branchTarget.labeledStmtClassificationSet.test(
1010               TargetStatementEnum::Branch) &&
1011           !branchTarget.labeledStmtClassificationSet.test(
1012               TargetStatementEnum::CompatibleBranch)) { // error
1013         context
1014             .Say(branchTarget.parserCharBlock,
1015                 "Label '%u' is not a branch target"_err_en_US, SayLabel(label))
1016             .Attach(stmt.parserCharBlock, "Control flow use of '%u'"_en_US,
1017                 SayLabel(label));
1018       } else if (!branchTarget.labeledStmtClassificationSet.test(
1019                      TargetStatementEnum::Branch)) { // warning
1020         context
1021             .Say(branchTarget.parserCharBlock,
1022                 "Label '%u' is not a branch target"_warn_en_US, SayLabel(label))
1023             .Attach(stmt.parserCharBlock, "Control flow use of '%u'"_en_US,
1024                 SayLabel(label));
1025       }
1026     }
1027   }
1028 }
1029 
1030 void CheckBranchConstraints(const SourceStmtList &branches,
1031     const TargetStmtMap &labels, const std::vector<ScopeInfo> &scopes,
1032     SemanticsContext &context) {
1033   CheckScopeConstraints(branches, labels, scopes, context);
1034   CheckBranchTargetConstraints(branches, labels, context);
1035 }
1036 
1037 void CheckDataXferTargetConstraints(const SourceStmtList &stmts,
1038     const TargetStmtMap &labels, SemanticsContext &context) {
1039   for (const auto &stmt : stmts) {
1040     const auto &label{stmt.parserLabel};
1041     auto ioTarget{GetLabel(labels, label)};
1042     if (HasScope(ioTarget.proxyForScope)) {
1043       if (!ioTarget.labeledStmtClassificationSet.test(
1044               TargetStatementEnum::Format)) {
1045         context
1046             .Say(ioTarget.parserCharBlock, "'%u' not a FORMAT"_err_en_US,
1047                 SayLabel(label))
1048             .Attach(stmt.parserCharBlock, "data transfer use of '%u'"_en_US,
1049                 SayLabel(label));
1050       }
1051     }
1052   }
1053 }
1054 
1055 void CheckDataTransferConstraints(const SourceStmtList &dataTransfers,
1056     const TargetStmtMap &labels, const std::vector<ScopeInfo> &scopes,
1057     SemanticsContext &context) {
1058   CheckScopeConstraints(dataTransfers, labels, scopes, context);
1059   CheckDataXferTargetConstraints(dataTransfers, labels, context);
1060 }
1061 
1062 void CheckAssignTargetConstraints(const SourceStmtList &stmts,
1063     const TargetStmtMap &labels, SemanticsContext &context) {
1064   for (const auto &stmt : stmts) {
1065     const auto &label{stmt.parserLabel};
1066     auto target{GetLabel(labels, label)};
1067     if (HasScope(target.proxyForScope) &&
1068         !target.labeledStmtClassificationSet.test(
1069             TargetStatementEnum::Branch) &&
1070         !target.labeledStmtClassificationSet.test(
1071             TargetStatementEnum::Format)) {
1072       context
1073           .Say(target.parserCharBlock,
1074               target.labeledStmtClassificationSet.test(
1075                   TargetStatementEnum::CompatibleBranch)
1076                   ? "Label '%u' is not a branch target or FORMAT"_warn_en_US
1077                   : "Label '%u' is not a branch target or FORMAT"_err_en_US,
1078               SayLabel(label))
1079           .Attach(stmt.parserCharBlock, "ASSIGN statement use of '%u'"_en_US,
1080               SayLabel(label));
1081     }
1082   }
1083 }
1084 
1085 void CheckAssignConstraints(const SourceStmtList &assigns,
1086     const TargetStmtMap &labels, const std::vector<ScopeInfo> &scopes,
1087     SemanticsContext &context) {
1088   CheckScopeConstraints(assigns, labels, scopes, context);
1089   CheckAssignTargetConstraints(assigns, labels, context);
1090 }
1091 
1092 bool CheckConstraints(ParseTreeAnalyzer &&parseTreeAnalysis) {
1093   auto &context{parseTreeAnalysis.ErrorHandler()};
1094   for (const auto &programUnit : parseTreeAnalysis.ProgramUnits()) {
1095     const auto &dos{programUnit.doStmtSources};
1096     const auto &branches{programUnit.otherStmtSources};
1097     const auto &labels{programUnit.targetStmts};
1098     const auto &scopes{programUnit.scopeModel};
1099     CheckLabelDoConstraints(dos, branches, labels, scopes, context);
1100     CheckBranchConstraints(branches, labels, scopes, context);
1101     const auto &dataTransfers{programUnit.formatStmtSources};
1102     CheckDataTransferConstraints(dataTransfers, labels, scopes, context);
1103     const auto &assigns{programUnit.assignStmtSources};
1104     CheckAssignConstraints(assigns, labels, scopes, context);
1105   }
1106   return !context.AnyFatalError();
1107 }
1108 
1109 bool ValidateLabels(SemanticsContext &context, const parser::Program &program) {
1110   return CheckConstraints(LabelAnalysis(context, program));
1111 }
1112 } // namespace Fortran::semantics
1113