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(
44       hasDescendant(binaryOperator(hasAnyOperatorName("==", "!="),
45                                    has(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       hasDescendant(cxxConstructExpr(hasDeclaration(cxxConstructorDecl(
53           isCopyConstructor(), ofClass(equalsBoundNode("class")))))));
54 
55   // In the template case, we need to handle two separate cases: 1) a local
56   // variable is created with the copy, 2) copy is created only as a temporary
57   // object.
58   const auto HasTemplateSelfCopy = cxxMethodDecl(
59       ofClass(cxxRecordDecl(hasAncestor(classTemplateDecl()))),
60       anyOf(hasDescendant(
61                 varDecl(hasType(cxxRecordDecl(equalsBoundNode("class"))),
62                         hasDescendant(parenListExpr()))),
63             hasDescendant(cxxUnresolvedConstructExpr(hasDescendant(declRefExpr(
64                 hasType(cxxRecordDecl(equalsBoundNode("class")))))))));
65 
66   // If inside the copy assignment operator another assignment operator is
67   // called on 'this' we assume that self-check might be handled inside
68   // this nested operator.
69   const auto HasNoNestedSelfAssign =
70       cxxMethodDecl(unless(hasDescendant(cxxMemberCallExpr(callee(cxxMethodDecl(
71           hasName("operator="), ofClass(equalsBoundNode("class"))))))));
72 
73   DeclarationMatcher AdditionalMatcher = cxxMethodDecl();
74   if (WarnOnlyIfThisHasSuspiciousField) {
75     // Matcher for standard smart pointers.
76     const auto SmartPointerType = qualType(hasUnqualifiedDesugaredType(
77         recordType(hasDeclaration(classTemplateSpecializationDecl(
78             hasAnyName("::std::shared_ptr", "::std::unique_ptr",
79                        "::std::weak_ptr", "::std::auto_ptr"),
80             templateArgumentCountIs(1))))));
81 
82     // We will warn only if the class has a pointer or a C array field which
83     // probably causes a problem during self-assignment (e.g. first resetting
84     // the pointer member, then trying to access the object pointed by the
85     // pointer, or memcpy overlapping arrays).
86     AdditionalMatcher = cxxMethodDecl(ofClass(cxxRecordDecl(
87         has(fieldDecl(anyOf(hasType(pointerType()), hasType(SmartPointerType),
88                             hasType(arrayType())))))));
89   }
90 
91   Finder->addMatcher(cxxMethodDecl(ofClass(cxxRecordDecl().bind("class")),
92                                    isCopyAssignmentOperator(), IsUserDefined,
93                                    HasReferenceParam, HasNoSelfCheck,
94                                    unless(HasNonTemplateSelfCopy),
95                                    unless(HasTemplateSelfCopy),
96                                    HasNoNestedSelfAssign, AdditionalMatcher)
97                          .bind("copyAssignmentOperator"),
98                      this);
99 }
100 
101 void UnhandledSelfAssignmentCheck::check(
102     const MatchFinder::MatchResult &Result) {
103   const auto *MatchedDecl =
104       Result.Nodes.getNodeAs<CXXMethodDecl>("copyAssignmentOperator");
105   diag(MatchedDecl->getLocation(),
106        "operator=() does not handle self-assignment properly");
107 }
108 
109 } // namespace bugprone
110 } // namespace tidy
111 } // namespace clang
112