UnhandledSelfAssignmentCheck.cpp

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//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
 
#include "UnhandledSelfAssignmentCheck.h"
#include "clang/AST/ASTContext.h"
#include "clang/ASTMatchers/ASTMatchFinder.h"
 
using namespace clang::ast_matchers;
 
namespace clang::tidy::bugprone {
 
UnhandledSelfAssignmentCheck::UnhandledSelfAssignmentCheck(
    StringRef Name, ClangTidyContext *Context)
    : ClangTidyCheck(Name, Context),
      WarnOnlyIfThisHasSuspiciousField(
          Options.get("WarnOnlyIfThisHasSuspiciousField", true)) {}
 
void UnhandledSelfAssignmentCheck::storeOptions(
    ClangTidyOptions::OptionMap &Opts) {
  Options.store(Opts, "WarnOnlyIfThisHasSuspiciousField",
                WarnOnlyIfThisHasSuspiciousField);
}
 
void UnhandledSelfAssignmentCheck::registerMatchers(MatchFinder *Finder) {
  // We don't care about deleted, default or implicit operator implementations.
  const auto IsUserDefined = cxxMethodDecl(
      isDefinition(), unless(anyOf(isDeleted(), isImplicit(), isDefaulted())));
 
  // We don't need to worry when a copy assignment operator gets the other
  // object by value.
  const auto HasReferenceParam =
      cxxMethodDecl(hasParameter(0, parmVarDecl(hasType(referenceType()))));
 
  // Self-check: Code compares something with 'this' pointer. We don't check
  // whether it is actually the parameter what we compare.
  const auto HasNoSelfCheck = cxxMethodDecl(unless(hasDescendant(
      binaryOperation(hasAnyOperatorName("==", "!="),
                      hasEitherOperand(ignoringParenCasts(cxxThisExpr()))))));
 
  // Both copy-and-swap and copy-and-move method creates a copy first and
  // assign it to 'this' with swap or move.
  // In the non-template case, we can search for the copy constructor call.
  const auto HasNonTemplateSelfCopy = cxxMethodDecl(
      ofClass(cxxRecordDecl(unless(hasAncestor(classTemplateDecl())))),
      traverse(TK_AsIs,
               hasDescendant(cxxConstructExpr(hasDeclaration(cxxConstructorDecl(
                   isCopyConstructor(), ofClass(equalsBoundNode("class"))))))));
 
  // In the template case, we need to handle two separate cases: 1) a local
  // variable is created with the copy, 2) copy is created only as a temporary
  // object.
  const auto HasTemplateSelfCopy = cxxMethodDecl(
      ofClass(cxxRecordDecl(hasAncestor(classTemplateDecl()))),
      anyOf(hasDescendant(
                varDecl(hasType(cxxRecordDecl(equalsBoundNode("class"))),
                        hasDescendant(parenListExpr()))),
            hasDescendant(cxxUnresolvedConstructExpr(hasDescendant(declRefExpr(
                hasType(cxxRecordDecl(equalsBoundNode("class")))))))));
 
  // If inside the copy assignment operator another assignment operator is
  // called on 'this' we assume that self-check might be handled inside
  // this nested operator.
  const auto HasNoNestedSelfAssign =
      cxxMethodDecl(unless(hasDescendant(cxxMemberCallExpr(callee(cxxMethodDecl(
          hasName("operator="), ofClass(equalsBoundNode("class"))))))));
 
  // Checking that some kind of constructor is called and followed by a `swap`:
  // T& operator=(const T& other) {
  //    T tmp{this->internal_data(), some, other, args};
  //    swap(tmp);
  //    return *this;
  // }
  const auto HasCopyAndSwap = cxxMethodDecl(
      ofClass(cxxRecordDecl()),
      hasBody(compoundStmt(
          hasDescendant(
              varDecl(hasType(cxxRecordDecl(equalsBoundNode("class"))))
                  .bind("tmp_var")),
          hasDescendant(stmt(anyOf(
              cxxMemberCallExpr(hasArgument(
                  0, declRefExpr(to(varDecl(equalsBoundNode("tmp_var")))))),
              callExpr(
                  callee(functionDecl(hasName("swap"))), argumentCountIs(2),
                  hasAnyArgument(
                      declRefExpr(to(varDecl(equalsBoundNode("tmp_var"))))),
                  hasAnyArgument(unaryOperator(has(cxxThisExpr()),
                                               hasOperatorName("*"))))))))));
 
  DeclarationMatcher AdditionalMatcher = cxxMethodDecl();
  if (WarnOnlyIfThisHasSuspiciousField) {
    // Matcher for standard smart pointers.
    const auto SmartPointerType = qualType(hasUnqualifiedDesugaredType(
        recordType(hasDeclaration(classTemplateSpecializationDecl(
            anyOf(allOf(hasAnyName("::std::shared_ptr", "::std::weak_ptr",
                                   "::std::auto_ptr"),
                        templateArgumentCountIs(1)),
                  allOf(hasName("::std::unique_ptr"),
                        templateArgumentCountIs(2))))))));
 
    // We will warn only if the class has a pointer or a C array field which
    // probably causes a problem during self-assignment (e.g. first resetting
    // the pointer member, then trying to access the object pointed by the
    // pointer, or memcpy overlapping arrays).
    AdditionalMatcher = cxxMethodDecl(ofClass(cxxRecordDecl(
        has(fieldDecl(anyOf(hasType(pointerType()), hasType(SmartPointerType),
                            hasType(arrayType())))))));
  }
 
  Finder->addMatcher(
      cxxMethodDecl(
          ofClass(cxxRecordDecl().bind("class")), isCopyAssignmentOperator(),
          IsUserDefined, HasReferenceParam, HasNoSelfCheck,
          unless(HasNonTemplateSelfCopy), unless(HasTemplateSelfCopy),
          unless(HasCopyAndSwap), HasNoNestedSelfAssign, AdditionalMatcher)
          .bind("copyAssignmentOperator"),
      this);
}
 
void UnhandledSelfAssignmentCheck::check(
    const MatchFinder::MatchResult &Result) {
  const auto *MatchedDecl =
      Result.Nodes.getNodeAs<CXXMethodDecl>("copyAssignmentOperator");
  diag(MatchedDecl->getLocation(),
       "operator=() does not handle self-assignment properly");
}
 
} // namespace clang::tidy::bugprone