[clang-tidy] Add new check: readability-redundant-typename

clang-tools-extra/clang-tidy/readability/CMakeLists.txt

@@ -49,6 +49,7 @@ add_clang_library(clangTidyReadabilityModule STATIC
   RedundantSmartptrGetCheck.cpp
   RedundantStringCStrCheck.cpp
   RedundantStringInitCheck.cpp
+  RedundantTypenameCheck.cpp
   ReferenceToConstructedTemporaryCheck.cpp
   SimplifyBooleanExprCheck.cpp
   SimplifySubscriptExprCheck.cpp

clang-tools-extra/clang-tidy/readability/ReadabilityTidyModule.cpp

@@ -52,6 +52,7 @@
 #include "RedundantSmartptrGetCheck.h"
 #include "RedundantStringCStrCheck.h"
 #include "RedundantStringInitCheck.h"
+#include "RedundantTypenameCheck.h"
 #include "ReferenceToConstructedTemporaryCheck.h"
 #include "SimplifyBooleanExprCheck.h"
 #include "SimplifySubscriptExprCheck.h"
@@ -143,6 +144,8 @@ class ReadabilityModule : public ClangTidyModule {
         "readability-redundant-parentheses");
     CheckFactories.registerCheck<RedundantPreprocessorCheck>(
         "readability-redundant-preprocessor");
+    CheckFactories.registerCheck<RedundantTypenameCheck>(
+        "readability-redundant-typename");
     CheckFactories.registerCheck<ReferenceToConstructedTemporaryCheck>(
         "readability-reference-to-constructed-temporary");
     CheckFactories.registerCheck<SimplifySubscriptExprCheck>(

clang-tools-extra/clang-tidy/readability/RedundantTypenameCheck.cpp

@@ -0,0 +1,86 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 "RedundantTypenameCheck.h"
+#include "clang/AST/TypeLoc.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
+#include "clang/Basic/Diagnostic.h"
+#include "clang/Lex/Lexer.h"
+#include "clang/Sema/DeclSpec.h"
+
+using namespace clang::ast_matchers;
+using namespace clang::ast_matchers::internal;
+
+namespace clang::tidy::readability {
+
+void RedundantTypenameCheck::registerMatchers(MatchFinder *Finder) {
+  Finder->addMatcher(typeLoc(unless(hasAncestor(decl(isInstantiated()))))
+                         .bind("nonDependentTypeLoc"),
+                     this);
+
+  if (!getLangOpts().CPlusPlus20)
+    return;
+
+  const auto InImplicitTypenameContext = anyOf(
+      hasParent(decl(anyOf(
+          typedefNameDecl(), templateTypeParmDecl(), nonTypeTemplateParmDecl(),
+          friendDecl(), fieldDecl(),
+          varDecl(hasDeclContext(anyOf(namespaceDecl(), translationUnitDecl())),
+                  unless(parmVarDecl())),
+          parmVarDecl(hasParent(expr(requiresExpr()))),
+          parmVarDecl(hasParent(typeLoc(hasParent(
+              decl(anyOf(cxxMethodDecl(), hasParent(friendDecl()),
+                         functionDecl(has(nestedNameSpecifier())))))))),
+          // Match return types.
+          functionDecl(unless(cxxConversionDecl()))))),
+      hasParent(expr(anyOf(cxxNamedCastExpr(), cxxNewExpr()))));
+  Finder->addMatcher(
+      typeLoc(InImplicitTypenameContext).bind("dependentTypeLoc"), this);
+}
+
+void RedundantTypenameCheck::check(const MatchFinder::MatchResult &Result) {
+  const SourceLocation ElaboratedKeywordLoc = [&] {
+    if (const auto *NonDependentTypeLoc =
+            Result.Nodes.getNodeAs<TypeLoc>("nonDependentTypeLoc")) {
+      if (const auto TTL = NonDependentTypeLoc->getAs<TypedefTypeLoc>())
+        return TTL.getElaboratedKeywordLoc();
+
+      if (const auto TTL = NonDependentTypeLoc->getAs<TagTypeLoc>())
+        return TTL.getElaboratedKeywordLoc();
+    } else {
+      TypeLoc InnermostTypeLoc =
+          *Result.Nodes.getNodeAs<TypeLoc>("dependentTypeLoc");
+      while (const TypeLoc Next = InnermostTypeLoc.getNextTypeLoc())
+        InnermostTypeLoc = Next;
+
+      if (const auto DNTL = InnermostTypeLoc.getAs<DependentNameTypeLoc>())
+        return DNTL.getElaboratedKeywordLoc();
+
+      if (const auto TSTL =
+              InnermostTypeLoc.getAs<TemplateSpecializationTypeLoc>())
+        return TSTL.getElaboratedKeywordLoc();
+    }
+
+    return SourceLocation();
+  }();
+
+  if (ElaboratedKeywordLoc.isInvalid())
+    return;
+
+  if (Token ElaboratedKeyword;
+      Lexer::getRawToken(ElaboratedKeywordLoc, ElaboratedKeyword,
+                         *Result.SourceManager, getLangOpts()) ||
+      ElaboratedKeyword.getRawIdentifier() != "typename")
+    return;
+
+  diag(ElaboratedKeywordLoc, "redundant 'typename'")
+      << FixItHint::CreateRemoval(ElaboratedKeywordLoc);
+}
+
+} // namespace clang::tidy::readability

clang-tools-extra/clang-tidy/readability/RedundantTypenameCheck.h

@@ -0,0 +1,36 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_READABILITY_REDUNDANTTYPENAMECHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_READABILITY_REDUNDANTTYPENAMECHECK_H
+
+#include "../ClangTidyCheck.h"
+
+namespace clang::tidy::readability {
+
+/// Finds redundant uses of the `typename` keyword.
+///
+/// For the user-facing documentation see:
+/// https://clang.llvm.org/extra/clang-tidy/checks/readability/redundant-typename.html
+class RedundantTypenameCheck : public ClangTidyCheck {
+public:
+  RedundantTypenameCheck(StringRef Name, ClangTidyContext *Context)
+      : ClangTidyCheck(Name, Context) {}
+  bool isLanguageVersionSupported(const LangOptions &LangOpts) const override {
+    return LangOpts.CPlusPlus;
+  }
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+  std::optional<TraversalKind> getCheckTraversalKind() const override {
+    return TK_IgnoreUnlessSpelledInSource;
+  }
+};
+
+} // namespace clang::tidy::readability
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_READABILITY_REDUNDANTTYPENAMECHECK_H

clang-tools-extra/docs/ReleaseNotes.rst

@@ -208,6 +208,13 @@ New checks
 
   Detect redundant parentheses.
 
+- New :doc:`readability-redundant-typename
+  <clang-tidy/checks/readability/redundant-typename>` check.
+
+  Finds redundant uses of the ``typename`` keyword. Can be used
+  to modernize code to take advantage of the C++20 rules that make
+  ``typename`` redundant in many cases where it was mandatory before.
+
 New check aliases
 ^^^^^^^^^^^^^^^^^
 

clang-tools-extra/docs/clang-tidy/checks/list.rst

@@ -409,6 +409,7 @@ Clang-Tidy Checks
    :doc:`readability-redundant-smartptr-get <readability/redundant-smartptr-get>`, "Yes"
    :doc:`readability-redundant-string-cstr <readability/redundant-string-cstr>`, "Yes"
    :doc:`readability-redundant-string-init <readability/redundant-string-init>`, "Yes"
+   :doc:`readability-redundant-typename <readability/redundant-typename>`, "Yes"
    :doc:`readability-reference-to-constructed-temporary <readability/reference-to-constructed-temporary>`,
    :doc:`readability-simplify-boolean-expr <readability/simplify-boolean-expr>`, "Yes"
    :doc:`readability-simplify-subscript-expr <readability/simplify-subscript-expr>`, "Yes"

clang-tools-extra/docs/clang-tidy/checks/readability/redundant-typename.rst

@@ -0,0 +1,26 @@
+.. title:: clang-tidy - readability-redundant-typename
+
+readability-redundant-typename
+==============================
+
+Finds redundant uses of the ``typename`` keyword.
+
+``typename`` is redundant in two cases. First, before non-dependent names:
+
+.. code-block:: c++
+
+  /* typename */ std::vector<int>::size_type size;
+
+And second, since C++20, before dependent names that appear in a context
+where only a type is allowed (the following example shows just a few of them):
+
+.. code-block:: c++
+
+  template <typename T>
+  using trait = /* typename */ T::type;
+
+  template <typename T>
+  struct S {
+    /* typename */ T::type variable;
+    /* typename */ T::type function(/* typename */ T::type);
+  };

clang-tools-extra/test/clang-tidy/checkers/readability/redundant-typename-cxx98.cpp

@@ -0,0 +1,19 @@
+// RUN: %check_clang_tidy -std=c++98,c++03 %s readability-redundant-typename %t \
+// RUN:   -- -- -fno-delayed-template-parsing
+
+struct NotDependent {
+  typedef int R;
+};
+
+template <typename T>
+typename T::R f() {
+  static_cast<typename T::R>(0);
+
+  typename NotDependent::R NotDependentVar;
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: redundant 'typename' [readability-redundant-typename]
+  // CHECK-FIXES: NotDependent::R NotDependentVar;
+
+  void notDependentFunctionDeclaration(typename NotDependent::R);
+  // CHECK-MESSAGES: :[[@LINE-1]]:40: warning: redundant 'typename' [readability-redundant-typename]
+  // CHECK-FIXES: void notDependentFunctionDeclaration(NotDependent::R);
+}