[clang-tools-extra] [clang-tidy] Support C++26 placeholder bindings (PR #207604)

[Yanzuo Liu via cfe-commits]

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@@ -0,0 +1,76 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 "UsePlaceholderBindingCheck.h"
+#include "../utils/DeclRefExprUtils.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 {
+
+namespace {
+AST_POLYMORPHIC_MATCHER(isInMacro,
+                        AST_POLYMORPHIC_SUPPORTED_TYPES(Stmt, Decl)) {
+  return Node.getBeginLoc().isMacroID() || Node.getEndLoc().isMacroID();
+}
+
+AST_MATCHER(VarDecl, hasAutomaticStorageDurationAndNoSpecifiers) {
+  return !Node.hasAttrs() && Node.getStorageClass() == SC_None &&
+         Node.getTSCSpec() == TSCS_unspecified;
+}
+} // namespace
+
+void UsePlaceholderBindingCheck::registerMatchers(MatchFinder *Finder) {
+  Finder->addMatcher(
+      cStyleCastExpr(
+          unless(isInMacro()), hasType(voidType()),
+          hasParent(stmt(anyOf(compoundStmt(), switchCase()))),
+          hasSourceExpression(ignoringParens(declRefExpr(
+              unless(isInMacro()),
+              to(bindingDecl(forDecomposition(varDecl(
+                                 unless(isInMacro()),
+                                 hasAutomaticStorageDurationAndNoSpecifiers(),
+                                 hasAncestor(compoundStmt().bind("scope")))))
+                     .bind("binding"))))))
+          .bind("cast"),
+      this);
+}
+
+void UsePlaceholderBindingCheck::check(const MatchFinder::MatchResult &Result) {
+  const auto *Cast = Result.Nodes.getNodeAs<CStyleCastExpr>("cast");
+  const auto *Binding = Result.Nodes.getNodeAs<BindingDecl>("binding");
+  const auto *Scope = Result.Nodes.getNodeAs<CompoundStmt>("scope");
+  ASTContext &Context = *Result.Context;
+
+  if (Binding->isParameterPack() ||
+      Binding->isPlaceholderVar(Context.getLangOpts()))
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zwuis wrote:

Move this to a custom AST matcher.

https://github.com/llvm/llvm-project/pull/207604