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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
36 lines
1.2 KiB
C++
36 lines
1.2 KiB
C++
//===--- MissingHashCheck.h - clang-tidy ------------------------*- C++ -*-===//
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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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#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_OBJC_MISSINGHASHCHECK_H
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#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_OBJC_MISSINGHASHCHECK_H
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#include "../ClangTidyCheck.h"
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namespace clang {
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namespace tidy {
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namespace objc {
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/// Finds Objective-C implementations that implement -isEqual: without also
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/// appropriately implementing -hash.
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///
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/// For the user-facing documentation see:
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/// http://clang.llvm.org/extra/clang-tidy/checks/objc-missing-hash.html
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class MissingHashCheck : public ClangTidyCheck {
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public:
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MissingHashCheck(StringRef Name, ClangTidyContext *Context)
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: ClangTidyCheck(Name, Context) {}
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void registerMatchers(ast_matchers::MatchFinder *Finder) override;
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void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
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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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#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_OBJC_MISSINGHASHCHECK_H
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