[clang] Implement CWG2428 "Deprecating a concept"

[Endilll]

This patch allows attributes to be attached to C++20 concepts, implementing CWG2428.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Vlad Serebrennikov (Endilll)

Changes

This patch allows attributes to be attached to C++20 concepts, implementing CWG2428.

---

Full diff: https://github.com/llvm/llvm-project/pull/92295.diff

5 Files Affected:

• (modified) clang/include/clang/Sema/Sema.h (+2-1)
• (modified) clang/lib/Parse/ParseTemplate.cpp (+9-6)
• (modified) clang/lib/Sema/SemaTemplate.cpp (+7-1)
• (modified) clang/test/CXX/drs/cwg24xx.cpp (+28)
• (modified) clang/www/cxx_dr_status.html (+17-5)

diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index 6a414aa57f32b..330076ca77371 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -9356,7 +9356,8 @@ class Sema final : public SemaBase {
   Decl *ActOnConceptDefinition(Scope *S,
                                MultiTemplateParamsArg TemplateParameterLists,
                                const IdentifierInfo *Name,
-                               SourceLocation NameLoc, Expr *ConstraintExpr);
+                               SourceLocation NameLoc, Expr *ConstraintExpr,
+                               const ParsedAttributesView &Attrs);
 
   void CheckConceptRedefinition(ConceptDecl *NewDecl, LookupResult &Previous,
                                 bool &AddToScope);
diff --git a/clang/lib/Parse/ParseTemplate.cpp b/clang/lib/Parse/ParseTemplate.cpp
index 665253a6674d2..b8f2b3f9657e7 100644
--- a/clang/lib/Parse/ParseTemplate.cpp
+++ b/clang/lib/Parse/ParseTemplate.cpp
@@ -167,9 +167,11 @@ Parser::DeclGroupPtrTy Parser::ParseTemplateDeclarationOrSpecialization(
                                   LastParamListWasEmpty);
 
   // Parse the actual template declaration.
-  if (Tok.is(tok::kw_concept))
-    return Actions.ConvertDeclToDeclGroup(
-        ParseConceptDefinition(TemplateInfo, DeclEnd));
+  if (Tok.is(tok::kw_concept)) {
+    Decl *ConceptDecl = ParseConceptDefinition(TemplateInfo, DeclEnd);
+    ParsingTemplateParams.complete(ConceptDecl);
+    return Actions.ConvertDeclToDeclGroup(ConceptDecl);
+  }
 
   return ParseDeclarationAfterTemplate(
       Context, TemplateInfo, ParsingTemplateParams, DeclEnd, AccessAttrs, AS);
@@ -316,7 +318,8 @@ Parser::ParseConceptDefinition(const ParsedTemplateInfo &TemplateInfo,
   const IdentifierInfo *Id = Result.Identifier;
   SourceLocation IdLoc = Result.getBeginLoc();
 
-  DiagnoseAndSkipCXX11Attributes();
+  ParsedAttributes Attrs(AttrFactory);
+  MaybeParseCXX11Attributes(Attrs);
 
   if (!TryConsumeToken(tok::equal)) {
     Diag(Tok.getLocation(), diag::err_expected) << tok::equal;
@@ -335,8 +338,8 @@ Parser::ParseConceptDefinition(const ParsedTemplateInfo &TemplateInfo,
   ExpectAndConsumeSemi(diag::err_expected_semi_declaration);
   Expr *ConstraintExpr = ConstraintExprResult.get();
   return Actions.ActOnConceptDefinition(getCurScope(),
-                                        *TemplateInfo.TemplateParams,
-                                        Id, IdLoc, ConstraintExpr);
+                                        *TemplateInfo.TemplateParams, Id, IdLoc,
+                                        ConstraintExpr, Attrs);
 }
 
 /// ParseTemplateParameters - Parses a template-parameter-list enclosed in
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index c7aac068e264b..2da933896b4da 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -5583,6 +5583,8 @@ Sema::CheckConceptTemplateId(const CXXScopeSpec &SS,
           /*UpdateArgsWithConversions=*/false))
     return ExprError();
 
+  DiagnoseUseOfDecl(NamedConcept, ConceptNameInfo.getLoc());
+
   auto *CSD = ImplicitConceptSpecializationDecl::Create(
       Context, NamedConcept->getDeclContext(), NamedConcept->getLocation(),
       CanonicalConverted);
@@ -9787,7 +9789,8 @@ Decl *Sema::ActOnTemplateDeclarator(Scope *S,
 
 Decl *Sema::ActOnConceptDefinition(
     Scope *S, MultiTemplateParamsArg TemplateParameterLists,
-    const IdentifierInfo *Name, SourceLocation NameLoc, Expr *ConstraintExpr) {
+    const IdentifierInfo *Name, SourceLocation NameLoc, Expr *ConstraintExpr,
+    const ParsedAttributesView &Attrs) {
   DeclContext *DC = CurContext;
 
   if (!DC->getRedeclContext()->isFileContext()) {
@@ -9849,6 +9852,9 @@ Decl *Sema::ActOnConceptDefinition(
   ActOnDocumentableDecl(NewDecl);
   if (AddToScope)
     PushOnScopeChains(NewDecl, S);
+
+  ProcessDeclAttributeList(S, NewDecl, Attrs);
+
   return NewDecl;
 }
 
diff --git a/clang/test/CXX/drs/cwg24xx.cpp b/clang/test/CXX/drs/cwg24xx.cpp
index 9f876cd870834..805a95c30470e 100644
--- a/clang/test/CXX/drs/cwg24xx.cpp
+++ b/clang/test/CXX/drs/cwg24xx.cpp
@@ -45,6 +45,34 @@ void fallthrough(int n) {
 #endif
 }
 
+namespace cwg2428 { // cwg2428: 19
+#if __cplusplus >= 202002L
+template <typename>
+concept C [[deprecated]] = true; // #C
+
+template <typename T>
+concept C3 = C<T>;
+// expected-warning@-1 {{'C' is deprecated}}
+//   expected-note@#C {{'C' has been explicitly marked deprecated here}}
+
+template <typename T, C U>
+// expected-warning@-1 {{'C' is deprecated}}
+//   expected-note@#C {{'C' has been explicitly marked deprecated here}}
+requires C<T>
+// expected-warning@-1 {{'C' is deprecated}}
+//   expected-note@#C {{'C' has been explicitly marked deprecated here}}
+void f() {
+  bool b = C<int>;
+  // expected-warning@-1 {{'C' is deprecated}}
+  //   expected-note@#C {{'C' has been explicitly marked deprecated here}}
+};
+
+void g(C auto a) {};
+// expected-warning@-1 {{'C' is deprecated}}
+//   expected-note@#C {{'C' has been explicitly marked deprecated here}}
+#endif
+} // namespace cwg2428
+
 namespace cwg2450 { // cwg2450: 18
 #if __cplusplus >= 202302L
 struct S {int a;};
diff --git a/clang/www/cxx_dr_status.html b/clang/www/cxx_dr_status.html
index 92fdcf5556ede..5e33b7492d81d 100755
--- a/clang/www/cxx_dr_status.html
+++ b/clang/www/cxx_dr_status.html
@@ -10698,7 +10698,7 @@ <h2 id="cxxdr">C++ defect report implementation status</h2>
     <td><a href="https://cplusplus.github.io/CWG/issues/1815.html">1815</a></td>
     <td>CD4</td>
     <td>Lifetime extension in aggregate initialization</td>
-    <td class="unreleased" align="center">Clang 19</td>
+    <td class="full" align="center">Yes</td>
   </tr>
   <tr id="1816">
     <td><a href="https://cplusplus.github.io/CWG/issues/1816.html">1816</a></td>
@@ -14376,7 +14376,7 @@ <h2 id="cxxdr">C++ defect report implementation status</h2>
     <td><a href="https://cplusplus.github.io/CWG/issues/2428.html">2428</a></td>
     <td>C++23</td>
     <td>Deprecating a concept</td>
-    <td class="unknown" align="center">Unknown</td>
+    <td class="unreleased" align="center">Clang 19</td>
   </tr>
   <tr id="2429">
     <td><a href="https://cplusplus.github.io/CWG/issues/2429.html">2429</a></td>
@@ -16985,7 +16985,7 @@ <h2 id="cxxdr">C++ defect report implementation status</h2>
   </tr>
   <tr class="open" id="2863">
     <td><a href="https://cplusplus.github.io/CWG/issues/2863.html">2863</a></td>
-    <td>tentatively ready</td>
+    <td>drafting</td>
     <td>Unclear synchronization requirements for object lifetime rules</td>
     <td align="center">Not resolved</td>
   </tr>
@@ -17021,13 +17021,13 @@ <h2 id="cxxdr">C++ defect report implementation status</h2>
   </tr>
   <tr class="open" id="2869">
     <td><a href="https://cplusplus.github.io/CWG/issues/2869.html">2869</a></td>
-    <td>open</td>
+    <td>review</td>
     <td><TT>this</TT> in local classes</td>
     <td align="center">Not resolved</td>
   </tr>
   <tr class="open" id="2870">
     <td><a href="https://cplusplus.github.io/CWG/issues/2870.html">2870</a></td>
-    <td>open</td>
+    <td>review</td>
     <td>Combining absent <I>encoding-prefix</I>es</td>
     <td align="center">Not resolved</td>
   </tr>
@@ -17138,6 +17138,18 @@ <h2 id="cxxdr">C++ defect report implementation status</h2>
     <td>open</td>
     <td>Missing cases for reference and array types for argument-dependent lookup</td>
     <td align="center">Not resolved</td>
+  </tr>
+  <tr class="open" id="2889">
+    <td><a href="https://cplusplus.github.io/CWG/issues/2889.html">2889</a></td>
+    <td>open</td>
+    <td>Requiring an accessible destructor for destroying operator delete</td>
+    <td align="center">Not resolved</td>
+  </tr>
+  <tr class="open" id="2890">
+    <td><a href="https://cplusplus.github.io/CWG/issues/2890.html">2890</a></td>
+    <td>open</td>
+    <td>Defining members of local classes</td>
+    <td align="center">Not resolved</td>
   </tr></table>
 
 </div>

[AaronBallman]

Please be sure to add a release note about implementing the DR.

[cor3ntin]

LGTM, thanks!