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Summary: Apple documentation states that: "If two objects are equal, they must have the same hash value. This last point is particularly important if you define isEqual: in a subclass and intend to put instances of that subclass into a collection. Make sure you also define hash in your subclass." https://developer.apple.com/documentation/objectivec/1418956-nsobject/1418795-isequal?language=objc In many or all versions of libobjc, -[NSObject isEqual:] is a pointer equality check and -[NSObject hash] returns the messaged object's pointer. A relatively common form of developer error is for a developer to override -isEqual: in a subclass without overriding -hash to ensure that hashes are equal for objects that are equal. It is assumed that an override of -isEqual: is a strong signal for changing the object's equality operator to something other than pointer equality which implies that a missing override of -hash could result in distinct objects being equal but having distinct hashes because they are independent instances. This added check flags classes that override -isEqual: but inherit NSObject's implementation of -hash to warn of the potential for unexpected behavior. The proper implementation of -hash is the responsibility of the developer and the check will only verify that the developer made an effort to properly implement -hash. Developers can set up unit tests to verify that their implementation of -hash is appropriate. Test Notes: Ran check-clang-tools. Reviewers: aaron.ballman, benhamilton Reviewed By: aaron.ballman Subscribers: Eugene.Zelenko, mgorny, xazax.hun, cfe-commits Tags: #clang Differential Revision: https://reviews.llvm.org/D67737 llvm-svn: 372445
63 lines
2.0 KiB
C++
63 lines
2.0 KiB
C++
//===--- MissingHashCheck.cpp - clang-tidy --------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#include "MissingHashCheck.h"
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#include "clang/AST/ASTContext.h"
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#include "clang/ASTMatchers/ASTMatchFinder.h"
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using namespace clang::ast_matchers;
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namespace clang {
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namespace tidy {
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namespace objc {
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namespace {
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AST_MATCHER_P(ObjCImplementationDecl, hasInterface,
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ast_matchers::internal::Matcher<ObjCInterfaceDecl>, Base) {
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const ObjCInterfaceDecl *InterfaceDecl = Node.getClassInterface();
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return Base.matches(*InterfaceDecl, Finder, Builder);
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}
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AST_MATCHER_P(ObjCContainerDecl, hasInstanceMethod,
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ast_matchers::internal::Matcher<ObjCMethodDecl>, Base) {
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// Check each instance method against the provided matcher.
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for (const auto *I : Node.instance_methods()) {
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if (Base.matches(*I, Finder, Builder))
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return true;
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}
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return false;
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}
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} // namespace
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void MissingHashCheck::registerMatchers(MatchFinder *Finder) {
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// This check should only be applied to Objective-C sources.
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if (!getLangOpts().ObjC)
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return;
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Finder->addMatcher(
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objcMethodDecl(
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hasName("isEqual:"), isInstanceMethod(),
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hasDeclContext(objcImplementationDecl(
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hasInterface(isDirectlyDerivedFrom("NSObject")),
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unless(hasInstanceMethod(hasName("hash"))))
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.bind("impl"))),
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this);
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}
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void MissingHashCheck::check(const MatchFinder::MatchResult &Result) {
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const auto *ID = Result.Nodes.getNodeAs<ObjCImplementationDecl>("impl");
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diag(ID->getLocation(), "%0 implements -isEqual: without implementing -hash")
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<< ID;
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}
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} // namespace objc
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} // namespace tidy
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} // namespace clang
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