1 //===--- MoveForwardingReferenceCheck.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 "MoveForwardingReferenceCheck.h"
10 #include "clang/Lex/Lexer.h"
11 #include "llvm/Support/raw_ostream.h"
12
13 #include <algorithm>
14
15 using namespace clang::ast_matchers;
16
17 namespace clang::tidy::bugprone {
18
replaceMoveWithForward(const UnresolvedLookupExpr * Callee,const ParmVarDecl * ParmVar,const TemplateTypeParmDecl * TypeParmDecl,DiagnosticBuilder & Diag,const ASTContext & Context)19 static void replaceMoveWithForward(const UnresolvedLookupExpr *Callee,
20 const ParmVarDecl *ParmVar,
21 const TemplateTypeParmDecl *TypeParmDecl,
22 DiagnosticBuilder &Diag,
23 const ASTContext &Context) {
24 const SourceManager &SM = Context.getSourceManager();
25 const LangOptions &LangOpts = Context.getLangOpts();
26
27 CharSourceRange CallRange =
28 Lexer::makeFileCharRange(CharSourceRange::getTokenRange(
29 Callee->getBeginLoc(), Callee->getEndLoc()),
30 SM, LangOpts);
31
32 if (CallRange.isValid()) {
33 const std::string TypeName =
34 (TypeParmDecl->getIdentifier() && !TypeParmDecl->isImplicit())
35 ? TypeParmDecl->getName().str()
36 : (llvm::Twine("decltype(") + ParmVar->getName() + ")").str();
37
38 const std::string ForwardName =
39 (llvm::Twine("forward<") + TypeName + ">").str();
40
41 // Create a replacement only if we see a "standard" way of calling
42 // std::move(). This will hopefully prevent erroneous replacements if the
43 // code does unusual things (e.g. create an alias for std::move() in
44 // another namespace).
45 NestedNameSpecifier *NNS = Callee->getQualifier();
46 if (!NNS) {
47 // Called as "move" (i.e. presumably the code had a "using std::move;").
48 // We still conservatively put a "std::" in front of the forward because
49 // we don't know whether the code also had a "using std::forward;".
50 Diag << FixItHint::CreateReplacement(CallRange, "std::" + ForwardName);
51 } else if (const NamespaceDecl *Namespace = NNS->getAsNamespace()) {
52 if (Namespace->getName() == "std") {
53 if (!NNS->getPrefix()) {
54 // Called as "std::move".
55 Diag << FixItHint::CreateReplacement(CallRange,
56 "std::" + ForwardName);
57 } else if (NNS->getPrefix()->getKind() == NestedNameSpecifier::Global) {
58 // Called as "::std::move".
59 Diag << FixItHint::CreateReplacement(CallRange,
60 "::std::" + ForwardName);
61 }
62 }
63 }
64 }
65 }
66
registerMatchers(MatchFinder * Finder)67 void MoveForwardingReferenceCheck::registerMatchers(MatchFinder *Finder) {
68 // Matches a ParmVarDecl for a forwarding reference, i.e. a non-const rvalue
69 // reference of a function template parameter type.
70 auto ForwardingReferenceParmMatcher =
71 parmVarDecl(
72 hasType(qualType(rValueReferenceType(),
73 references(templateTypeParmType(hasDeclaration(
74 templateTypeParmDecl().bind("type-parm-decl")))),
75 unless(references(qualType(isConstQualified()))))))
76 .bind("parm-var");
77
78 Finder->addMatcher(
79 callExpr(callee(unresolvedLookupExpr(
80 hasAnyDeclaration(namedDecl(
81 hasUnderlyingDecl(hasName("::std::move")))))
82 .bind("lookup")),
83 argumentCountIs(1),
84 hasArgument(0, ignoringParenImpCasts(declRefExpr(
85 to(ForwardingReferenceParmMatcher)))))
86 .bind("call-move"),
87 this);
88 }
89
check(const MatchFinder::MatchResult & Result)90 void MoveForwardingReferenceCheck::check(
91 const MatchFinder::MatchResult &Result) {
92 const auto *CallMove = Result.Nodes.getNodeAs<CallExpr>("call-move");
93 const auto *UnresolvedLookup =
94 Result.Nodes.getNodeAs<UnresolvedLookupExpr>("lookup");
95 const auto *ParmVar = Result.Nodes.getNodeAs<ParmVarDecl>("parm-var");
96 const auto *TypeParmDecl =
97 Result.Nodes.getNodeAs<TemplateTypeParmDecl>("type-parm-decl");
98
99 // Get the FunctionDecl and FunctionTemplateDecl containing the function
100 // parameter.
101 const auto *FuncForParam = dyn_cast<FunctionDecl>(ParmVar->getDeclContext());
102 if (!FuncForParam)
103 return;
104 const FunctionTemplateDecl *FuncTemplate =
105 FuncForParam->getDescribedFunctionTemplate();
106 if (!FuncTemplate)
107 return;
108
109 // Check that the template type parameter belongs to the same function
110 // template as the function parameter of that type. (This implies that type
111 // deduction will happen on the type.)
112 const TemplateParameterList *Params = FuncTemplate->getTemplateParameters();
113 if (!llvm::is_contained(*Params, TypeParmDecl))
114 return;
115
116 auto Diag = diag(CallMove->getExprLoc(),
117 "forwarding reference passed to std::move(), which may "
118 "unexpectedly cause lvalues to be moved; use "
119 "std::forward() instead");
120
121 replaceMoveWithForward(UnresolvedLookup, ParmVar, TypeParmDecl, Diag,
122 *Result.Context);
123 }
124
125 } // namespace clang::tidy::bugprone
126