1 //===--- ForwardingReferenceOverloadCheck.cpp - clang-tidy-----------------===//
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 "ForwardingReferenceOverloadCheck.h"
10 #include "clang/AST/ASTContext.h"
11 #include "clang/ASTMatchers/ASTMatchFinder.h"
12 #include <algorithm>
13 
14 using namespace clang::ast_matchers;
15 
16 namespace clang {
17 namespace tidy {
18 namespace bugprone {
19 
20 namespace {
21 // Check if the given type is related to std::enable_if.
22 AST_MATCHER(QualType, isEnableIf) {
23   auto CheckTemplate = [](const TemplateSpecializationType *Spec) {
24     if (!Spec || !Spec->getTemplateName().getAsTemplateDecl()) {
25       return false;
26     }
27     const NamedDecl *TypeDecl =
28         Spec->getTemplateName().getAsTemplateDecl()->getTemplatedDecl();
29     return TypeDecl->isInStdNamespace() &&
30            (TypeDecl->getName().equals("enable_if") ||
31             TypeDecl->getName().equals("enable_if_t"));
32   };
33   const Type *BaseType = Node.getTypePtr();
34   // Case: pointer or reference to enable_if.
35   while (BaseType->isPointerType() || BaseType->isReferenceType()) {
36     BaseType = BaseType->getPointeeType().getTypePtr();
37   }
38   // Case: type parameter dependent (enable_if<is_integral<T>>).
39   if (const auto *Dependent = BaseType->getAs<DependentNameType>()) {
40     BaseType = Dependent->getQualifier()->getAsType();
41   }
42   if (!BaseType)
43     return false;
44   if (CheckTemplate(BaseType->getAs<TemplateSpecializationType>())) {
45     return true; // Case: enable_if_t< >.
46   } else if (const auto *Elaborated = BaseType->getAs<ElaboratedType>()) {
47     if (const auto *Qualifier = Elaborated->getQualifier()->getAsType()) {
48       if (CheckTemplate(Qualifier->getAs<TemplateSpecializationType>())) {
49         return true; // Case: enable_if< >::type.
50       }
51     }
52   }
53   return false;
54 }
55 AST_MATCHER_P(TemplateTypeParmDecl, hasDefaultArgument,
56               clang::ast_matchers::internal::Matcher<QualType>, TypeMatcher) {
57   return Node.hasDefaultArgument() &&
58          TypeMatcher.matches(Node.getDefaultArgument(), Finder, Builder);
59 }
60 } // namespace
61 
62 void ForwardingReferenceOverloadCheck::registerMatchers(MatchFinder *Finder) {
63   // Forwarding references require C++11 or later.
64   if (!getLangOpts().CPlusPlus11)
65     return;
66 
67   auto ForwardingRefParm =
68       parmVarDecl(
69           hasType(qualType(rValueReferenceType(),
70                            references(templateTypeParmType(hasDeclaration(
71                                templateTypeParmDecl().bind("type-parm-decl")))),
72                            unless(references(isConstQualified())))))
73           .bind("parm-var");
74 
75   DeclarationMatcher findOverload =
76       cxxConstructorDecl(
77           hasParameter(0, ForwardingRefParm),
78           unless(hasAnyParameter(
79               // No warning: enable_if as constructor parameter.
80               parmVarDecl(hasType(isEnableIf())))),
81           unless(hasParent(functionTemplateDecl(has(templateTypeParmDecl(
82               // No warning: enable_if as type parameter.
83               hasDefaultArgument(isEnableIf())))))))
84           .bind("ctor");
85   Finder->addMatcher(findOverload, this);
86 }
87 
88 void ForwardingReferenceOverloadCheck::check(
89     const MatchFinder::MatchResult &Result) {
90   const auto *ParmVar = Result.Nodes.getNodeAs<ParmVarDecl>("parm-var");
91   const auto *TypeParmDecl =
92       Result.Nodes.getNodeAs<TemplateTypeParmDecl>("type-parm-decl");
93 
94   // Get the FunctionDecl and FunctionTemplateDecl containing the function
95   // parameter.
96   const auto *FuncForParam = dyn_cast<FunctionDecl>(ParmVar->getDeclContext());
97   if (!FuncForParam)
98     return;
99   const FunctionTemplateDecl *FuncTemplate =
100       FuncForParam->getDescribedFunctionTemplate();
101   if (!FuncTemplate)
102     return;
103 
104   // Check that the template type parameter belongs to the same function
105   // template as the function parameter of that type. (This implies that type
106   // deduction will happen on the type.)
107   const TemplateParameterList *Params = FuncTemplate->getTemplateParameters();
108   if (!llvm::is_contained(*Params, TypeParmDecl))
109     return;
110 
111   // Every parameter after the first must have a default value.
112   const auto *Ctor = Result.Nodes.getNodeAs<CXXConstructorDecl>("ctor");
113   for (auto Iter = Ctor->param_begin() + 1; Iter != Ctor->param_end(); ++Iter) {
114     if (!(*Iter)->hasDefaultArg())
115       return;
116   }
117   bool EnabledCopy = false, DisabledCopy = false, EnabledMove = false,
118        DisabledMove = false;
119   for (const auto *OtherCtor : Ctor->getParent()->ctors()) {
120     if (OtherCtor->isCopyOrMoveConstructor()) {
121       if (OtherCtor->isDeleted() || OtherCtor->getAccess() == AS_private)
122         (OtherCtor->isCopyConstructor() ? DisabledCopy : DisabledMove) = true;
123       else
124         (OtherCtor->isCopyConstructor() ? EnabledCopy : EnabledMove) = true;
125     }
126   }
127   bool Copy = (!EnabledMove && !DisabledMove && !DisabledCopy) || EnabledCopy;
128   bool Move = !DisabledMove || EnabledMove;
129   if (!Copy && !Move)
130     return;
131   diag(Ctor->getLocation(),
132        "constructor accepting a forwarding reference can "
133        "hide the %select{copy|move|copy and move}0 constructor%s1")
134       << (Copy && Move ? 2 : (Copy ? 0 : 1)) << Copy + Move;
135   for (const auto *OtherCtor : Ctor->getParent()->ctors()) {
136     if (OtherCtor->isCopyOrMoveConstructor() && !OtherCtor->isDeleted() &&
137         OtherCtor->getAccess() != AS_private) {
138       diag(OtherCtor->getLocation(),
139            "%select{copy|move}0 constructor declared here", DiagnosticIDs::Note)
140           << OtherCtor->isMoveConstructor();
141     }
142   }
143 }
144 
145 } // namespace bugprone
146 } // namespace tidy
147 } // namespace clang
148