1 //===--- UnhandledSelfAssignmentCheck.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 "UnhandledSelfAssignmentCheck.h"
10 #include "clang/AST/ASTContext.h"
11 #include "clang/ASTMatchers/ASTMatchFinder.h"
12 
13 using namespace clang::ast_matchers;
14 
15 namespace clang {
16 namespace tidy {
17 namespace bugprone {
18 
19 UnhandledSelfAssignmentCheck::UnhandledSelfAssignmentCheck(
20     StringRef Name, ClangTidyContext *Context)
21     : ClangTidyCheck(Name, Context),
22       WarnOnlyIfThisHasSuspiciousField(
23           Options.get("WarnOnlyIfThisHasSuspiciousField", true)) {}
24 
25 void UnhandledSelfAssignmentCheck::storeOptions(
26     ClangTidyOptions::OptionMap &Opts) {
27   Options.store(Opts, "WarnOnlyIfThisHasSuspiciousField",
28                 WarnOnlyIfThisHasSuspiciousField);
29 }
30 
31 void UnhandledSelfAssignmentCheck::registerMatchers(MatchFinder *Finder) {
32   // We don't care about deleted, default or implicit operator implementations.
33   const auto IsUserDefined = cxxMethodDecl(
34       isDefinition(), unless(anyOf(isDeleted(), isImplicit(), isDefaulted())));
35 
36   // We don't need to worry when a copy assignment operator gets the other
37   // object by value.
38   const auto HasReferenceParam =
39       cxxMethodDecl(hasParameter(0, parmVarDecl(hasType(referenceType()))));
40 
41   // Self-check: Code compares something with 'this' pointer. We don't check
42   // whether it is actually the parameter what we compare.
43   const auto HasNoSelfCheck = cxxMethodDecl(unless(hasDescendant(
44       binaryOperation(hasAnyOperatorName("==", "!="),
45                       hasEitherOperand(ignoringParenCasts(cxxThisExpr()))))));
46 
47   // Both copy-and-swap and copy-and-move method creates a copy first and
48   // assign it to 'this' with swap or move.
49   // In the non-template case, we can search for the copy constructor call.
50   const auto HasNonTemplateSelfCopy = cxxMethodDecl(
51       ofClass(cxxRecordDecl(unless(hasAncestor(classTemplateDecl())))),
52       traverse(TK_AsIs,
53                hasDescendant(cxxConstructExpr(hasDeclaration(cxxConstructorDecl(
54                    isCopyConstructor(), ofClass(equalsBoundNode("class"))))))));
55 
56   // In the template case, we need to handle two separate cases: 1) a local
57   // variable is created with the copy, 2) copy is created only as a temporary
58   // object.
59   const auto HasTemplateSelfCopy = cxxMethodDecl(
60       ofClass(cxxRecordDecl(hasAncestor(classTemplateDecl()))),
61       anyOf(hasDescendant(
62                 varDecl(hasType(cxxRecordDecl(equalsBoundNode("class"))),
63                         hasDescendant(parenListExpr()))),
64             hasDescendant(cxxUnresolvedConstructExpr(hasDescendant(declRefExpr(
65                 hasType(cxxRecordDecl(equalsBoundNode("class")))))))));
66 
67   // If inside the copy assignment operator another assignment operator is
68   // called on 'this' we assume that self-check might be handled inside
69   // this nested operator.
70   const auto HasNoNestedSelfAssign =
71       cxxMethodDecl(unless(hasDescendant(cxxMemberCallExpr(callee(cxxMethodDecl(
72           hasName("operator="), ofClass(equalsBoundNode("class"))))))));
73 
74   DeclarationMatcher AdditionalMatcher = cxxMethodDecl();
75   if (WarnOnlyIfThisHasSuspiciousField) {
76     // Matcher for standard smart pointers.
77     const auto SmartPointerType = qualType(hasUnqualifiedDesugaredType(
78         recordType(hasDeclaration(classTemplateSpecializationDecl(
79             hasAnyName("::std::shared_ptr", "::std::unique_ptr",
80                        "::std::weak_ptr", "::std::auto_ptr"),
81             templateArgumentCountIs(1))))));
82 
83     // We will warn only if the class has a pointer or a C array field which
84     // probably causes a problem during self-assignment (e.g. first resetting
85     // the pointer member, then trying to access the object pointed by the
86     // pointer, or memcpy overlapping arrays).
87     AdditionalMatcher = cxxMethodDecl(ofClass(cxxRecordDecl(
88         has(fieldDecl(anyOf(hasType(pointerType()), hasType(SmartPointerType),
89                             hasType(arrayType())))))));
90   }
91 
92   Finder->addMatcher(cxxMethodDecl(ofClass(cxxRecordDecl().bind("class")),
93                                    isCopyAssignmentOperator(), IsUserDefined,
94                                    HasReferenceParam, HasNoSelfCheck,
95                                    unless(HasNonTemplateSelfCopy),
96                                    unless(HasTemplateSelfCopy),
97                                    HasNoNestedSelfAssign, AdditionalMatcher)
98                          .bind("copyAssignmentOperator"),
99                      this);
100 }
101 
102 void UnhandledSelfAssignmentCheck::check(
103     const MatchFinder::MatchResult &Result) {
104   const auto *MatchedDecl =
105       Result.Nodes.getNodeAs<CXXMethodDecl>("copyAssignmentOperator");
106   diag(MatchedDecl->getLocation(),
107        "operator=() does not handle self-assignment properly");
108 }
109 
110 } // namespace bugprone
111 } // namespace tidy
112 } // namespace clang
113