[clang-tools-extra] [llvm] [clangd] Add CodeAction to swap operands to binary operators (PR #78999)

[Julian Schmidt via cfe-commits]

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@@ -0,0 +1,210 @@
+//===--- SwapBinaryOperands.cpp ----------------------------------*- C++-*-===//
+//
+// 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 "ParsedAST.h"
+#include "SourceCode.h"
+#include "refactor/Tweak.h"
+#include "support/Logger.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/AST/Expr.h"
+#include "clang/AST/OperationKinds.h"
+#include "clang/AST/Stmt.h"
+#include "clang/Basic/LangOptions.h"
+#include "clang/Basic/SourceLocation.h"
+#include "clang/Basic/SourceManager.h"
+#include "clang/Tooling/Core/Replacement.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/Casting.h"
+#include "llvm/Support/Error.h"
+
+namespace clang {
+namespace clangd {
+namespace {
+/// Check whether it makes logical sense to swap operands to an operator.
+/// Assignment or member access operators are rarely swappable
+/// while keeping the meaning intact, whereas comparison operators, mathematical
+/// operators, etc. are often desired to be swappable for readability, avoiding
+/// bugs by assigning to nullptr when comparison was desired, etc.
+auto isOpSwappable(const BinaryOperatorKind Opcode) -> bool {
+  switch (Opcode) {
+  case BinaryOperatorKind::BO_Mul:
+  case BinaryOperatorKind::BO_Add:
+  case BinaryOperatorKind::BO_Cmp:
----------------
5chmidti wrote:

`<=>` is not commutative,

```c++
const auto a = 3 <=> 5;
assert(std::is_lt(a));
const auto b = 5 <=> 3;
assert(std::is_lt(b)); // failure
```

https://github.com/llvm/llvm-project/pull/78999