[clang-tools-extra] [clang-tidy] Add readability-constant-operand-order check (PR #167158)

[via cfe-commits]

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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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_READABILITY_CONSTANTOPERANDORDERCHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_READABILITY_CONSTANTOPERANDORDERCHECK_H
+
+#include "../ClangTidyCheck.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+#include <string>
+#include <vector>
+
+namespace clang::tidy::readability {
+/// Finds binary expressions where the constant operand appears on the
+/// non-preferred side (configurable) and offers a fix-it that swaps operands
+/// (and inverts the operator for asymmetric operators like `<` / `>`).
+/// Options
+///  - BinaryOperators: comma-separated list of operators to check
+///      (default: "==,!=,<,<=,>,>=")
+///  - PreferredConstantSide: "Left" or "Right" (default: "Right")
+class ConstantOperandOrderCheck : public ClangTidyCheck {
+public:
+  ConstantOperandOrderCheck(StringRef Name, ClangTidyContext *Context);
+  ~ConstantOperandOrderCheck() override;
+
+  // Persist options so they show up in config files.
+  void storeOptions(ClangTidyOptions::OptionMap &Opts) override;
+
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+
+  bool isLanguageVersionSupported(const LangOptions &LangOpts) const override {
+    // This check is primarily for C/C++, keep it limited to C++ for now.
+    return LangOpts.CPlusPlus;
+  }
+
+private:
+  // Option keys (used when storing & reading options)
+  static constexpr llvm::StringLiteral BinaryOperatorsOption =
+      "BinaryOperators";
+  static constexpr llvm::StringLiteral PreferredSideOption =
+      "PreferredConstantSide";
+
+  // Runtime values, populated from Options in the constructor (or storeOptions)
+  std::string PreferredSide;          // "Left" or "Right"
+  std::vector<std::string> Operators; // list of operator names, e.g. "=="
+
+  // Implementation helpers live in the .cpp file.
----------------
EugeneZelenko wrote:

```suggestion
```

Useless comment.

https://github.com/llvm/llvm-project/pull/167158