[clang-tools-extra] [clang-tidy] Add `modernize-use-as-const` check (PR #210554)

[Lucas Ly Ba via cfe-commits]

================
@@ -0,0 +1,85 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 "UseAsConstCheck.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/Lex/Lexer.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::modernize {
+
+UseAsConstCheck::UseAsConstCheck(StringRef Name, ClangTidyContext *Context)
+    : ClangTidyCheck(Name, Context),
+      Inserter(Options.getLocalOrGlobal("IncludeStyle",
+                                        utils::IncludeSorter::IS_LLVM),
+               areDiagsSelfContained()) {}
+
+void UseAsConstCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
+  Options.store(Opts, "IncludeStyle", Inserter.getStyle());
+}
+
+void UseAsConstCheck::registerMatchers(MatchFinder *Finder) {
+  // Match a static_cast to a const-qualified type; check() narrows it down.
+  Finder->addMatcher(
+      cxxStaticCastExpr(hasType(qualType(isConstQualified()))).bind("cast"),
+      this);
+}
+
+void UseAsConstCheck::registerPPCallbacks(const SourceManager &SM,
+                                          Preprocessor *PP,
+                                          Preprocessor *ModuleExpanderPP) {
+  Inserter.registerPreprocessor(PP);
+}
+
+void UseAsConstCheck::check(const MatchFinder::MatchResult &Result) {
+  const auto *Cast = Result.Nodes.getNodeAs<CXXStaticCastExpr>("cast");
+  // A cast written in a macro cannot be safely rewritten.
+  if (Cast->getBeginLoc().isMacroID() || Cast->getEndLoc().isMacroID())
+    return;
+
+  // Only handle a cast written as 'const T &'.
+  const auto *RefType = Cast->getTypeAsWritten()->getAs<LValueReferenceType>();
+  if (!RefType)
+    return;
+  QualType Pointee = RefType->getPointeeType();
+  if (!Pointee.isConstQualified())
+    return;
----------------
lucasly-ba wrote:

the cast expression's own type is the pointee, so the & only shows up as written, will add some !

https://github.com/llvm/llvm-project/pull/210554