[clang] Fix missing diagnostic of declaration use when accessing TypeDecls through typename access (#129681)

We were missing a call to DiagnoseUseOfDecl when performing typename
access.

This refactors the code so that TypeDecl lookups funnel through a helper
which performs all the necessary checks, removing some related
duplication on the way.

Fixes #58547

Differential Revision: https://reviews.llvm.org/D136533

Author: mizvekov

clang/docs/ReleaseNotes.rst

@@ -35,6 +35,9 @@ Potentially Breaking Changes
 ============================
 
 - The Objective-C ARC migrator (ARCMigrate) has been removed.
+- Fix missing diagnostics for uses of declarations when performing typename access,
+  such as when performing member access on a '[[deprecated]]' type alias.
+  (#GH58547)
 
 C/C++ Language Potentially Breaking Changes
 -------------------------------------------

clang/include/clang/Sema/Sema.h

@@ -3168,6 +3168,13 @@ class Sema final : public SemaBase {
 
   DeclGroupPtrTy ConvertDeclToDeclGroup(Decl *Ptr, Decl *OwnedType = nullptr);
 
+  enum class DiagCtorKind { None, Implicit, Typename };
+  /// Returns the TypeDeclType for the given type declaration,
+  /// as ASTContext::getTypeDeclType would, but
+  /// performs the required semantic checks for name lookup of said entity.
+  QualType getTypeDeclType(DeclContext *LookupCtx, DiagCtorKind DCK,
+                           TypeDecl *TD, SourceLocation NameLoc);
+
   /// If the identifier refers to a type name within this scope,
   /// return the declaration of that type.
   ///

clang/lib/Sema/SemaDecl.cpp

@@ -137,6 +137,26 @@ class TypeNameValidatorCCC final : public CorrectionCandidateCallback {
 
 } // end anonymous namespace
 
+QualType Sema::getTypeDeclType(DeclContext *LookupCtx, DiagCtorKind DCK,
+                               TypeDecl *TD, SourceLocation NameLoc) {
+  auto *LookupRD = dyn_cast_or_null<CXXRecordDecl>(LookupCtx);
+  auto *FoundRD = dyn_cast<CXXRecordDecl>(TD);
+  if (DCK != DiagCtorKind::None && LookupRD && FoundRD &&
+      FoundRD->isInjectedClassName() &&
+      declaresSameEntity(LookupRD, cast<Decl>(FoundRD->getParent()))) {
+    Diag(NameLoc,
+         DCK == DiagCtorKind::Typename
+             ? diag::ext_out_of_line_qualified_id_type_names_constructor
+             : diag::err_out_of_line_qualified_id_type_names_constructor)
+        << TD->getIdentifier() << /*Type=*/1
+        << 0 /*if any keyword was present, it was 'typename'*/;
+  }
+
+  DiagnoseUseOfDecl(TD, NameLoc);
+  MarkAnyDeclReferenced(TD->getLocation(), TD, /*OdrUse=*/false);
+  return Context.getTypeDeclType(TD);
+}
+
 namespace {
 enum class UnqualifiedTypeNameLookupResult {
   NotFound,
@@ -293,10 +313,11 @@ ParsedType Sema::getTypeName(const IdentifierInfo &II, SourceLocation NameLoc,
                              bool IsClassTemplateDeductionContext,
                              ImplicitTypenameContext AllowImplicitTypename,
                              IdentifierInfo **CorrectedII) {
+  bool IsImplicitTypename = !isClassName && !IsCtorOrDtorName;
   // FIXME: Consider allowing this outside C++1z mode as an extension.
   bool AllowDeducedTemplate = IsClassTemplateDeductionContext &&
-                              getLangOpts().CPlusPlus17 && !IsCtorOrDtorName &&
-                              !isClassName && !HasTrailingDot;
+                              getLangOpts().CPlusPlus17 && IsImplicitTypename &&
+                              !HasTrailingDot;
 
   // Determine where we will perform name lookup.
   DeclContext *LookupCtx = nullptr;
@@ -320,11 +341,9 @@ ParsedType Sema::getTypeName(const IdentifierInfo &II, SourceLocation NameLoc,
         // refer to a member of an unknown specialization.
         // In C++2a, in several contexts a 'typename' is not required. Also
         // allow this as an extension.
-        if (AllowImplicitTypename == ImplicitTypenameContext::No &&
-            !isClassName && !IsCtorOrDtorName)
-          return nullptr;
-        bool IsImplicitTypename = !isClassName && !IsCtorOrDtorName;
         if (IsImplicitTypename) {
+          if (AllowImplicitTypename == ImplicitTypenameContext::No)
+            return nullptr;
           SourceLocation QualifiedLoc = SS->getRange().getBegin();
           if (getLangOpts().CPlusPlus20)
             Diag(QualifiedLoc, diag::warn_cxx17_compat_implicit_typename);
@@ -513,18 +532,10 @@ ParsedType Sema::getTypeName(const IdentifierInfo &II, SourceLocation NameLoc,
     // C++ [class.qual]p2: A lookup that would find the injected-class-name
     // instead names the constructors of the class, except when naming a class.
     // This is ill-formed when we're not actually forming a ctor or dtor name.
-    auto *LookupRD = dyn_cast_or_null<CXXRecordDecl>(LookupCtx);
-    auto *FoundRD = dyn_cast<CXXRecordDecl>(TD);
-    if (!isClassName && !IsCtorOrDtorName && LookupRD && FoundRD &&
-        FoundRD->isInjectedClassName() &&
-        declaresSameEntity(LookupRD, cast<Decl>(FoundRD->getParent())))
-      Diag(NameLoc, diag::err_out_of_line_qualified_id_type_names_constructor)
-          << &II << /*Type*/1;
-
-    DiagnoseUseOfDecl(IIDecl, NameLoc);
-
-    T = Context.getTypeDeclType(TD);
-    MarkAnyDeclReferenced(TD->getLocation(), TD, /*OdrUse=*/false);
+    T = getTypeDeclType(LookupCtx,
+                        IsImplicitTypename ? DiagCtorKind::Implicit
+                                           : DiagCtorKind::None,
+                        TD, NameLoc);
   } else if (ObjCInterfaceDecl *IDecl = dyn_cast<ObjCInterfaceDecl>(IIDecl)) {
     (void)DiagnoseUseOfDecl(IDecl, NameLoc);
     if (!HasTrailingDot)

clang/lib/Sema/SemaTemplate.cpp

@@ -10914,20 +10914,15 @@ Sema::CheckTypenameType(ElaboratedTypeKeyword Keyword,
       //
       // FIXME: That's not strictly true: mem-initializer-id lookup does not
       // ignore functions, but that appears to be an oversight.
-      auto *LookupRD = dyn_cast_or_null<CXXRecordDecl>(Ctx);
-      auto *FoundRD = dyn_cast<CXXRecordDecl>(Type);
-      if (Keyword == ElaboratedTypeKeyword::Typename && LookupRD && FoundRD &&
-          FoundRD->isInjectedClassName() &&
-          declaresSameEntity(LookupRD, cast<Decl>(FoundRD->getParent())))
-        Diag(IILoc, diag::ext_out_of_line_qualified_id_type_names_constructor)
-            << &II << 1 << 0 /*'typename' keyword used*/;
-
+      QualType T = getTypeDeclType(Ctx,
+                                   Keyword == ElaboratedTypeKeyword::Typename
+                                       ? DiagCtorKind::Typename
+                                       : DiagCtorKind::None,
+                                   Type, IILoc);
       // We found a type. Build an ElaboratedType, since the
       // typename-specifier was just sugar.
-      MarkAnyDeclReferenced(Type->getLocation(), Type, /*OdrUse=*/false);
-      return Context.getElaboratedType(Keyword,
-                                       QualifierLoc.getNestedNameSpecifier(),
-                                       Context.getTypeDeclType(Type));
+      return Context.getElaboratedType(
+          Keyword, QualifierLoc.getNestedNameSpecifier(), T);
     }
 
     // C++ [dcl.type.simple]p2:

clang/test/CXX/dcl.dcl/dcl.attr/dcl.attr.deprecated/p1.cpp

@@ -58,3 +58,17 @@ template <typename T>
   FunS2 f;// No warning, entire function is deprecated, so usage here should be fine.
 
 }
+
+namespace GH58547 {
+struct A {
+  using ta [[deprecated]] = int; // expected-note 2{{marked deprecated here}}
+};
+
+using t1 = typename A::ta; // expected-warning {{'ta' is deprecated}}
+
+template <class B1> struct B {
+  using tb = typename B1::ta; // expected-warning {{'ta' is deprecated}}
+};
+
+template struct B<A>; // expected-note {{requested here}}
+} // namespace GH58547