1 //===--- MoveConstructorInitCheck.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 "MoveConstructorInitCheck.h"
10 #include "../utils/Matchers.h"
11 #include "clang/AST/ASTContext.h"
12 #include "clang/ASTMatchers/ASTMatchFinder.h"
13 
14 using namespace clang::ast_matchers;
15 
16 namespace clang {
17 namespace tidy {
18 namespace performance {
19 
20 MoveConstructorInitCheck::MoveConstructorInitCheck(StringRef Name,
21                                                    ClangTidyContext *Context)
22     : ClangTidyCheck(Name, Context) {}
23 
24 void MoveConstructorInitCheck::registerMatchers(MatchFinder *Finder) {
25   Finder->addMatcher(
26       traverse(TK_AsIs,
27                cxxConstructorDecl(
28                    unless(isImplicit()), isMoveConstructor(),
29                    hasAnyConstructorInitializer(
30                        cxxCtorInitializer(
31                            withInitializer(cxxConstructExpr(hasDeclaration(
32                                cxxConstructorDecl(isCopyConstructor())
33                                    .bind("ctor")))))
34                            .bind("move-init")))),
35       this);
36 }
37 
38 void MoveConstructorInitCheck::check(const MatchFinder::MatchResult &Result) {
39   const auto *CopyCtor = Result.Nodes.getNodeAs<CXXConstructorDecl>("ctor");
40   const auto *Initializer =
41       Result.Nodes.getNodeAs<CXXCtorInitializer>("move-init");
42 
43   // Do not diagnose if the expression used to perform the initialization is a
44   // trivially-copyable type.
45   QualType QT = Initializer->getInit()->getType();
46   if (QT.isTriviallyCopyableType(*Result.Context))
47     return;
48 
49   if (QT.isConstQualified())
50     return;
51 
52   const auto *RD = QT->getAsCXXRecordDecl();
53   if (RD && RD->isTriviallyCopyable())
54     return;
55 
56   // Diagnose when the class type has a move constructor available, but the
57   // ctor-initializer uses the copy constructor instead.
58   const CXXConstructorDecl *Candidate = nullptr;
59   for (const auto *Ctor : CopyCtor->getParent()->ctors()) {
60     if (Ctor->isMoveConstructor() && Ctor->getAccess() <= AS_protected &&
61         !Ctor->isDeleted()) {
62       // The type has a move constructor that is at least accessible to the
63       // initializer.
64       //
65       // FIXME: Determine whether the move constructor is a viable candidate
66       // for the ctor-initializer, perhaps provide a fix-it that suggests
67       // using std::move().
68       Candidate = Ctor;
69       break;
70     }
71   }
72 
73   if (Candidate) {
74     // There's a move constructor candidate that the caller probably intended
75     // to call instead.
76     diag(Initializer->getSourceLocation(),
77          "move constructor initializes %select{class member|base class}0 by "
78          "calling a copy constructor")
79         << Initializer->isBaseInitializer();
80     diag(CopyCtor->getLocation(), "copy constructor being called",
81          DiagnosticIDs::Note);
82     diag(Candidate->getLocation(), "candidate move constructor here",
83          DiagnosticIDs::Note);
84   }
85 }
86 
87 } // namespace performance
88 } // namespace tidy
89 } // namespace clang
90