[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:
+  case BinaryOperatorKind::BO_LT:
+  case BinaryOperatorKind::BO_GT:
+  case BinaryOperatorKind::BO_LE:
+  case BinaryOperatorKind::BO_GE:
+  case BinaryOperatorKind::BO_EQ:
+  case BinaryOperatorKind::BO_NE:
+  case BinaryOperatorKind::BO_And:
+  case BinaryOperatorKind::BO_Xor:
+  case BinaryOperatorKind::BO_Or:
+  case BinaryOperatorKind::BO_LAnd:
+  case BinaryOperatorKind::BO_LOr:
+  case BinaryOperatorKind::BO_Comma:
+    return true;
+  // Noncommutative operators:
+  case BinaryOperatorKind::BO_Div:
+  case BinaryOperatorKind::BO_Sub:
+  case BinaryOperatorKind::BO_Shl:
+  case BinaryOperatorKind::BO_Shr:
+  case BinaryOperatorKind::BO_Rem:
+  // Member access:
+  case BinaryOperatorKind::BO_PtrMemD:
+  case BinaryOperatorKind::BO_PtrMemI:
+  // Assignment:
+  case BinaryOperatorKind::BO_Assign:
+  case BinaryOperatorKind::BO_MulAssign:
+  case BinaryOperatorKind::BO_DivAssign:
+  case BinaryOperatorKind::BO_RemAssign:
+  case BinaryOperatorKind::BO_AddAssign:
+  case BinaryOperatorKind::BO_SubAssign:
+  case BinaryOperatorKind::BO_ShlAssign:
+  case BinaryOperatorKind::BO_ShrAssign:
+  case BinaryOperatorKind::BO_AndAssign:
+  case BinaryOperatorKind::BO_XorAssign:
+  case BinaryOperatorKind::BO_OrAssign:
+    return false;
+  }
+  return false;
+}
+
+/// Some operators are asymmetric and need to be flipped when swapping their
+/// operands
+/// @param[out] Opcode the opcode to potentially swap
+/// If the opcode does not need to be swapped or is not swappable, does nothing
+void swapOperator(BinaryOperatorKind &Opcode) {
----------------
5chmidti wrote:

If you change this function to return the potentially changed operator kind, then the initialization of `SwappedOperator` can be made `const`.

`BinaryOperatorKind swapOperator(BinaryOperatorKind Opcode) { ... }`

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