Unverified Commit a671e795 authored by Victor Chernyakin's avatar Victor Chernyakin Committed by GitHub
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[clang] Implement CWG2413 (implicit `typename` in conversion operators) (#195207) 

Link: [CWG2413](https://wg21.link/cwg2413). This DR was resolved by
[P1787R6](https://wg21.link/P1787R6) by adding the following wording to
[[temp.res.general]/4](https://eel.is/c++draft/temp.res.general#4):

> A [type-only
context](https://eel.is/c++draft/temp.res.general#def:context,type-only)
is defined as follows: A qualified or unqualified name is said to be in
a type-only context if it is the terminal name of
> - ...
> - a [type-specifier](https://eel.is/c++draft/dcl.type.general#nt:type-specifier) of a
>   - ...
> - [conversion-type-id](https://eel.is/c++draft/class.conv.fct#nt:conversion-type-id),

Towards #54150.
parent 7c881dd2

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

+2 −1
Original line number Diff line number Diff line
@@ -34,7 +34,8 @@ void RedundantTypenameCheck::registerMatchers(MatchFinder *Finder) { 
                    cxxMethodDecl(), hasParent(friendDecl()),

                    functionDecl(has(nestedNameSpecifier())),

                    cxxDeductionGuideDecl(hasDeclContext(recordDecl())))))))),

                // Match return types.

                // Match return types. FIXME: CWG2413 made conversion operators

                // an implicit typename context.

                functionDecl(unless(cxxConversionDecl()))))),

            hasParent(expr(anyOf(cxxNamedCastExpr(), cxxNewExpr()))));

  Finder->addMatcher(

clang/docs/ReleaseNotes.rst

+3 −0
Original line number Diff line number Diff line
@@ -158,6 +158,9 @@ C++17 Feature Support 
Resolutions to C++ Defect Reports

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^



- Clang now allows omitting ``typename`` before a template name in a

  conversion operator, implementing `CWG2413 <https://wg21.link/cwg2413>`_.



C Language Changes

------------------

clang/include/clang/Parse/Parser.h

+1 −1
Original line number Diff line number Diff line
@@ -1685,13 +1685,13 @@ private: 
    case DeclSpecContext::DSC_alias_declaration:

    case DeclSpecContext::DSC_template_param:

    case DeclSpecContext::DSC_new:

    case DeclSpecContext::DSC_conv_operator:

      return ImplicitTypenameContext::Yes;



    case DeclSpecContext::DSC_normal:

    case DeclSpecContext::DSC_objc_method_result:

    case DeclSpecContext::DSC_condition:

    case DeclSpecContext::DSC_template_arg:

    case DeclSpecContext::DSC_conv_operator:

    case DeclSpecContext::DSC_association:

      return ImplicitTypenameContext::No;

    }

clang/lib/Parse/ParseDecl.cpp

+1 −4
Original line number Diff line number Diff line
@@ -3365,11 +3365,8 @@ void Parser::ParseDeclarationSpecifiers( 


  // If we are in a operator context, convert it back into a type specifier

  // context for better error handling later on.

  if (DSContext == DeclSpecContext::DSC_conv_operator) {

    // No implicit typename here.

    AllowImplicitTypename = ImplicitTypenameContext::No;

  if (DSContext == DeclSpecContext::DSC_conv_operator)

    DSContext = DeclSpecContext::DSC_type_specifier;

  }



  bool EnteringContext = (DSContext == DeclSpecContext::DSC_class ||

                          DSContext == DeclSpecContext::DSC_top_level);

clang/test/CXX/drs/cwg24xx.cpp

+14 −4
Original line number Diff line number Diff line 
// RUN: %clang_cc1 -std=c++98 -fexceptions -fcxx-exceptions -pedantic-errors %s -verify-directives -verify=expected,cxx98-14

// RUN: %clang_cc1 -std=c++11 -fexceptions -fcxx-exceptions -pedantic-errors %s -verify-directives -verify=expected,cxx98-14

// RUN: %clang_cc1 -std=c++14 -fexceptions -fcxx-exceptions -pedantic-errors %s -verify-directives -verify=expected,cxx98-14

// RUN: %clang_cc1 -std=c++17 -fexceptions -fcxx-exceptions -pedantic-errors %s -verify-directives -verify=expected,since-cxx17

// RUN: %clang_cc1 -std=c++98 -fexceptions -fcxx-exceptions -pedantic-errors %s -verify-directives -verify=expected,cxx98-14,cxx98-17

// RUN: %clang_cc1 -std=c++11 -fexceptions -fcxx-exceptions -pedantic-errors %s -verify-directives -verify=expected,cxx98-14,cxx98-17

// RUN: %clang_cc1 -std=c++14 -fexceptions -fcxx-exceptions -pedantic-errors %s -verify-directives -verify=expected,cxx98-14,cxx98-17

// RUN: %clang_cc1 -std=c++17 -fexceptions -fcxx-exceptions -pedantic-errors %s -verify-directives -verify=expected,since-cxx17,cxx98-17

// RUN: %clang_cc1 -std=c++20 -fexceptions -fcxx-exceptions -pedantic-errors %s -verify-directives -verify=expected,since-cxx20,since-cxx17

// RUN: %clang_cc1 -std=c++23 -fexceptions -fcxx-exceptions -pedantic-errors %s -verify-directives -verify=expected,since-cxx20,since-cxx17

// RUN: %clang_cc1 -std=c++2c -fexceptions -fcxx-exceptions -pedantic-errors %s -verify-directives -verify=expected,since-cxx20,since-cxx17



// cwg2406 is in cwg2406.cpp



namespace cwg2413 { // cwg2413: 23

template <typename T>

struct S {

  operator T::R();

  // cxx98-17-error@-1 {{missing 'typename' prior to dependent type name 'T::R' is a C++20 extension}}

  void f() { operator T::R(); }

  // cxx98-17-error@-1 {{missing 'typename' prior to dependent type name 'T::R' is a C++20 extension}}

};

} // namespace cwg2413



namespace cwg2428 { // cwg2428: 19

#if __cplusplus >= 202002L

template <typename>