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

[Julian Schmidt via cfe-commits]

================
@@ -0,0 +1,139 @@
+//===--- UseStdMinMaxCheck.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 "UseStdMinMaxCheck.h"
+#include "../utils/ASTUtils.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/Lex/Preprocessor.h"
+#include <optional>
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::readability {
+
+UseStdMinMaxCheck::UseStdMinMaxCheck(StringRef Name, ClangTidyContext *Context)
+    : ClangTidyCheck(Name, Context),
+      IncludeInserter(Options.getLocalOrGlobal("IncludeStyle",
+                                               utils::IncludeSorter::IS_LLVM),
+                      areDiagsSelfContained()) {}
+
+void UseStdMinMaxCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
+  Options.store(Opts, "IncludeStyle", IncludeInserter.getStyle());
+  Options.store(Opts, "AlgorithmHeader",
+                Options.get("AlgorithmHeader", "<algorithm>"));
+}
+
+void UseStdMinMaxCheck::registerMatchers(MatchFinder *Finder) {
+  Finder->addMatcher(
+      ifStmt(
+          hasCondition(binaryOperator(hasAnyOperatorName("<", ">", "<=", ">="),
+                                      hasLHS(expr().bind("CondLhs")),
+                                      hasRHS(expr().bind("CondRhs")))),
+          hasThen(anyOf(stmt(binaryOperator(hasOperatorName("="),
+                                            hasLHS(expr().bind("AssignLhs")),
+                                            hasRHS(expr().bind("AssignRhs")))),
+                        compoundStmt(has(binaryOperator(
+                                         hasOperatorName("="),
+                                         hasLHS(expr().bind("AssignLhs")),
+                                         hasRHS(expr().bind("AssignRhs")))))
+                            .bind("compound"))))
+          .bind("if"),
+      this);
+}
+
+void UseStdMinMaxCheck::registerPPCallbacks(const SourceManager &SM,
+                                            Preprocessor *PP,
+                                            Preprocessor *ModuleExpanderPP) {
+  IncludeInserter.registerPreprocessor(PP);
+}
+
+void UseStdMinMaxCheck::check(const MatchFinder::MatchResult &Result) {
+  const auto *CondLhs = Result.Nodes.getNodeAs<Expr>("CondLhs");
+  const auto *CondRhs = Result.Nodes.getNodeAs<Expr>("CondRhs");
+  const auto *AssignLhs = Result.Nodes.getNodeAs<Expr>("AssignLhs");
+  const auto *AssignRhs = Result.Nodes.getNodeAs<Expr>("AssignRhs");
+  const auto *If = Result.Nodes.getNodeAs<IfStmt>("if");
+  const auto *Compound = Result.Nodes.getNodeAs<CompoundStmt>("compound");
+  const auto &Context = *Result.Context;
+  const auto &LO = Context.getLangOpts();
+  const SourceManager &Source = Context.getSourceManager();
+
+  const auto *BinaryOp = dyn_cast<BinaryOperator>(If->getCond());
+  if (!BinaryOp || If->hasElseStorage())
+    return;
+
+  if (Compound) {
+    if (Compound->size() > 1)
+      return;
+  }
+
+  const SourceLocation IfLocation = If->getIfLoc();
+  const SourceLocation ThenLocation = If->getEndLoc();
+
+  if (IfLocation.isMacroID() || ThenLocation.isMacroID())
+    return;
+
+  const auto CreateString = [&](int index) -> llvm::StringRef {
+    switch (index) {
+    case 1:
+      return Lexer::getSourceText(
+          Source.getExpansionRange(CondLhs->getSourceRange()), Source, LO);
+    case 2:
+      return Lexer::getSourceText(
+          Source.getExpansionRange(CondRhs->getSourceRange()), Source, LO);
+    case 3:
+      return Lexer::getSourceText(
+          Source.getExpansionRange(AssignLhs->getSourceRange()), Source, LO);
+    default:
+      return "Invalid index";
+    }
+  };
+
+  const auto CreateReplacement = [&](bool useMax) {
+    std::string functionName = useMax ? "std::max" : "std::min";
+    return CreateString(/* AssignLhs */ 3).str() + " = " + functionName + "(" +
+           CreateString(/* CondLhs */ 1).str() + ", " +
+           CreateString(/* CondRhs */ 2).str() + ");";
+  };
----------------
5chmidti wrote:

I think that the `switch` and `index` are hurting readability.
Because you merged the creation for min and max into a single `CreateReplacement` lambda I camek up with this:
create the strings for `AssignLhs`, `CondLhs` and `CondRhs` inside the `CreateReplacement` lambda.
E.g.:
```c++
  const auto CreateReplacement = [&](bool UseMax) {
    const auto *FunctionName = UseMax ? "std::max" : "std::min";
    const auto AssignLhsStr = Lexer::...;
    const auto CondLhsStr = Lexer::...;
    const auto CondRhsStr = Lexer::...;
    return (AssignLhsStr + " = " + FunctionName + "(" +
           CondLhsStr + ", " +
           CondRhsStr + ");").str();
  };
```
Then there is only one lambda that handles the whole replacement string generation.
Also, `UseMax`, `FunctionName` :)

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