[clang-tools-extra] Add clang-tidy check to suggest replacement of conditional statement with std::min/std::max (PR #77816)

[Piotr Zegar via cfe-commits]

================
@@ -0,0 +1,88 @@
+//===--- ConditionaltostdminmaxCheck.cpp - clang-tidy ---------------------===//
+//
+// 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 "ConditionaltostdminmaxCheck.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::readability {
+
+void ConditionaltostdminmaxCheck::registerMatchers(MatchFinder *Finder) {
+  Finder->addMatcher(
+      ifStmt(has(binaryOperator(
+                 anyOf(hasOperatorName("<"), hasOperatorName(">")),
+                 hasLHS(ignoringImpCasts(declRefExpr().bind("lhsVar1"))),
+                 hasRHS(ignoringImpCasts(declRefExpr().bind("rhsVar1"))))),
+             hasThen(stmt(binaryOperator(
+                 hasOperatorName("="),
+                 hasLHS(ignoringImpCasts(declRefExpr().bind("lhsVar2"))),
+                 hasRHS(ignoringImpCasts(declRefExpr().bind("rhsVar2")))))))
+          .bind("ifStmt"),
+      this);
+}
+
+void ConditionaltostdminmaxCheck::check(
+    const MatchFinder::MatchResult &Result) {
+  const DeclRefExpr *lhsVar1 = Result.Nodes.getNodeAs<DeclRefExpr>("lhsVar1");
+  const DeclRefExpr *rhsVar1 = Result.Nodes.getNodeAs<DeclRefExpr>("rhsVar1");
+  const DeclRefExpr *lhsVar2 = Result.Nodes.getNodeAs<DeclRefExpr>("lhsVar2");
+  const DeclRefExpr *rhsVar2 = Result.Nodes.getNodeAs<DeclRefExpr>("rhsVar2");
+  const IfStmt *ifStmt = Result.Nodes.getNodeAs<IfStmt>("ifStmt");
+
+  if (!lhsVar1 || !rhsVar1 || !lhsVar2 || !rhsVar2 || !ifStmt)
+    return;
+
+  const BinaryOperator *binaryOp = dyn_cast<BinaryOperator>(ifStmt->getCond());
+  if (!binaryOp)
+    return;
+
+  SourceLocation ifLocation = ifStmt->getIfLoc();
+  SourceLocation thenLocation = ifStmt->getEndLoc();
+
+  if (binaryOp->getOpcode() == BO_LT) {
+    if (lhsVar1->getDecl() == lhsVar2->getDecl() &&
+        rhsVar1->getDecl() == rhsVar2->getDecl()) {
+      diag(ifStmt->getIfLoc(), "use std::max instead of <")
+          << FixItHint::CreateReplacement(
+                 SourceRange(ifLocation, thenLocation),
+                 lhsVar2->getNameInfo().getAsString() + " = std::max(" +
+                     lhsVar1->getNameInfo().getAsString() + ", " +
----------------
PiotrZSL wrote:

instead of trying to read variable name, just use [CreateInsertionFromRange](https://clang.llvm.org/doxygen/classclang_1_1FixItHint.html#a0d8406a70566d4b3937cd5b11a2c520f) or in worst case Lexer::getText to actually read what is there.

https://github.com/llvm/llvm-project/pull/77816