[clang] [clang-tools-extra] [clang] Implement CWG2413 (implicit `typename` in conversion operators) (PR #195207)

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llvmorg-github-actions[bot] wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang-tidy

Author: Victor Chernyakin (localspook)

<details>
<summary>Changes</summary>

Link: [CWG2413](https://wg21.link/cwg2413).

Towards #<!-- -->54150.

---
Full diff: https://github.com/llvm/llvm-project/pull/195207.diff


7 Files Affected:

- (modified) clang-tools-extra/clang-tidy/readability/RedundantTypenameCheck.cpp (+2-1) 
- (modified) clang/docs/ReleaseNotes.rst (+3) 
- (modified) clang/include/clang/Parse/Parser.h (+1-1) 
- (modified) clang/lib/Parse/ParseDecl.cpp (+1-4) 
- (modified) clang/test/CXX/drs/cwg24xx.cpp (+10) 
- (modified) clang/test/CXX/temp/temp.res/p4.cpp (+2-2) 
- (modified) clang/www/cxx_dr_status.html (+1-1) 


``````````diff
diff --git a/clang-tools-extra/clang-tidy/readability/RedundantTypenameCheck.cpp b/clang-tools-extra/clang-tidy/readability/RedundantTypenameCheck.cpp
index 77ef2b8622c93..33359fdc3f4bc 100644
--- a/clang-tools-extra/clang-tidy/readability/RedundantTypenameCheck.cpp
+++ b/clang-tools-extra/clang-tidy/readability/RedundantTypenameCheck.cpp
@@ -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(
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index c5c8c1fa12e7a..44750a1485a49 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -155,6 +155,9 @@ 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
 ------------------
 
diff --git a/clang/include/clang/Parse/Parser.h b/clang/include/clang/Parse/Parser.h
index 1d07d8dbcfa01..7c89a88dd37ff 100644
--- a/clang/include/clang/Parse/Parser.h
+++ b/clang/include/clang/Parse/Parser.h
@@ -1685,13 +1685,13 @@ class Parser : public CodeCompletionHandler {
     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;
     }
diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
index 4f37e1471c29e..03b68cc88369b 100644
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -3364,11 +3364,8 @@ 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);
diff --git a/clang/test/CXX/drs/cwg24xx.cpp b/clang/test/CXX/drs/cwg24xx.cpp
index 0a6a05c125451..2acdf42da7275 100644
--- a/clang/test/CXX/drs/cwg24xx.cpp
+++ b/clang/test/CXX/drs/cwg24xx.cpp
@@ -8,6 +8,16 @@
 
 // cwg2406 is in cwg2406.cpp
 
+namespace cwg2413 { // cwg2413: 23
+#if __cplusplus >= 202002L
+template <typename T>
+struct S {
+  operator T::R();
+  void f() { operator T::R(); }
+};
+#endif
+} // namespace cwg2413
+
 namespace cwg2428 { // cwg2428: 19
 #if __cplusplus >= 202002L
 template <typename>
diff --git a/clang/test/CXX/temp/temp.res/p4.cpp b/clang/test/CXX/temp/temp.res/p4.cpp
index 9dbdd235e925d..6ca609b58cf2c 100644
--- a/clang/test/CXX/temp/temp.res/p4.cpp
+++ b/clang/test/CXX/temp/temp.res/p4.cpp
@@ -157,8 +157,8 @@ template int Test<X>;
 
 template<typename T> struct A {
   enum E : T::type {}; // expected-error{{missing 'typename'}}
-  operator T::type() {} // expected-error{{missing 'typename'}}
-  void f() { this->operator T::type(); } // expected-error{{missing 'typename'}}
+  operator T::type() {}
+  void f() { this->operator T::type(); }
 };
 
 template<typename T>
diff --git a/clang/www/cxx_dr_status.html b/clang/www/cxx_dr_status.html
index 2a1e79471ceea..ffb0494cd884d 100755
--- a/clang/www/cxx_dr_status.html
+++ b/clang/www/cxx_dr_status.html
@@ -16684,7 +16684,7 @@ <h2 id="cxxdr">C++ defect report implementation status</h2>
     <td>[<a href="https://wg21.link/temp.res">temp.res</a>]</td>
     <td>CD6</td>
     <td><TT>typename</TT> in <I>conversion-function-id</I>s</td>
-    <td class="unknown" align="center">Unknown</td>
+    <td class="full" align="center">Clang 23</td>
   </tr>
   <tr id="2414">
     <td><a href="https://cplusplus.github.io/CWG/issues/2414.html">2414</a></td>

``````````

</details>


https://github.com/llvm/llvm-project/pull/195207