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   if (!getLangOpts().CPlusPlus)
33     return;
34 
35   // We don't care about deleted, default or implicit operator implementations.
36   const auto IsUserDefined = cxxMethodDecl(
37       isDefinition(), unless(anyOf(isDeleted(), isImplicit(), isDefaulted())));
38 
39   // We don't need to worry when a copy assignment operator gets the other
40   // object by value.
41   const auto HasReferenceParam =
42       cxxMethodDecl(hasParameter(0, parmVarDecl(hasType(referenceType()))));
43 
44   // Self-check: Code compares something with 'this' pointer. We don't check
45   // whether it is actually the parameter what we compare.
46   const auto HasNoSelfCheck = cxxMethodDecl(unless(hasDescendant(
47       binaryOperator(anyOf(hasOperatorName("=="), hasOperatorName("!=")),
48                      has(ignoringParenCasts(cxxThisExpr()))))));
49 
50   // Both copy-and-swap and copy-and-move method creates a copy first and
51   // assign it to 'this' with swap or move.
52   // In the non-template case, we can search for the copy constructor call.
53   const auto HasNonTemplateSelfCopy = cxxMethodDecl(
54       ofClass(cxxRecordDecl(unless(hasAncestor(classTemplateDecl())))),
55       hasDescendant(cxxConstructExpr(hasDeclaration(cxxConstructorDecl(
56           isCopyConstructor(), ofClass(equalsBoundNode("class")))))));
57 
58   // In the template case, we need to handle two separate cases: 1) a local
59   // variable is created with the copy, 2) copy is created only as a temporary
60   // object.
61   const auto HasTemplateSelfCopy = cxxMethodDecl(
62       ofClass(cxxRecordDecl(hasAncestor(classTemplateDecl()))),
63       anyOf(hasDescendant(
64                 varDecl(hasType(cxxRecordDecl(equalsBoundNode("class"))),
65                         hasDescendant(parenListExpr()))),
66             hasDescendant(cxxUnresolvedConstructExpr(hasDescendant(declRefExpr(
67                 hasType(cxxRecordDecl(equalsBoundNode("class")))))))));
68 
69   // If inside the copy assignment operator another assignment operator is
70   // called on 'this' we assume that self-check might be handled inside
71   // this nested operator.
72   const auto HasNoNestedSelfAssign =
73       cxxMethodDecl(unless(hasDescendant(cxxMemberCallExpr(callee(cxxMethodDecl(
74           hasName("operator="), ofClass(equalsBoundNode("class"))))))));
75 
76   DeclarationMatcher AdditionalMatcher = cxxMethodDecl();
77   if (WarnOnlyIfThisHasSuspiciousField) {
78     // Matcher for standard smart pointers.
79     const auto SmartPointerType = qualType(hasUnqualifiedDesugaredType(
80         recordType(hasDeclaration(classTemplateSpecializationDecl(
81             hasAnyName("::std::shared_ptr", "::std::unique_ptr",
82                        "::std::weak_ptr", "::std::auto_ptr"),
83             templateArgumentCountIs(1))))));
84 
85     // We will warn only if the class has a pointer or a C array field which
86     // probably causes a problem during self-assignment (e.g. first resetting
87     // the pointer member, then trying to access the object pointed by the
88     // pointer, or memcpy overlapping arrays).
89     AdditionalMatcher = cxxMethodDecl(ofClass(cxxRecordDecl(
90         has(fieldDecl(anyOf(hasType(pointerType()), hasType(SmartPointerType),
91                             hasType(arrayType())))))));
92   }
93 
94   Finder->addMatcher(cxxMethodDecl(ofClass(cxxRecordDecl().bind("class")),
95                                    isCopyAssignmentOperator(), IsUserDefined,
96                                    HasReferenceParam, HasNoSelfCheck,
97                                    unless(HasNonTemplateSelfCopy),
98                                    unless(HasTemplateSelfCopy),
99                                    HasNoNestedSelfAssign, AdditionalMatcher)
100                          .bind("copyAssignmentOperator"),
101                      this);
102 }
103 
104 void UnhandledSelfAssignmentCheck::check(
105     const MatchFinder::MatchResult &Result) {
106   const auto *MatchedDecl =
107       Result.Nodes.getNodeAs<CXXMethodDecl>("copyAssignmentOperator");
108   diag(MatchedDecl->getLocation(),
109        "operator=() does not handle self-assignment properly");
110 }
111 
112 } // namespace bugprone
113 } // namespace tidy
114 } // namespace clang
115