[Clang][Sema] Allow access to a public template alias declaration that refers to friend's private nested type

[jcsxky]

This patch attempts to fix #25708
Current access check missed qualifier(NestedNameSpecifier) in friend class checking. Add it to Records of EffectiveContext by changing the DeclContext makes MatchesFriend work.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Qizhi Hu (jcsxky)

Changes

---

Full diff: https://github.com/llvm/llvm-project/pull/83847.diff

4 Files Affected:

• (modified) clang/include/clang/Sema/Lookup.h (+5)
• (modified) clang/lib/Sema/SemaAccess.cpp (+19)
• (modified) clang/lib/Sema/SemaTemplate.cpp (+1)
• (added) clang/test/SemaTemplate/PR25708.cpp (+23)

diff --git a/clang/include/clang/Sema/Lookup.h b/clang/include/clang/Sema/Lookup.h
index 2f2f2607a937fe..a07609bfb7c9bc 100644
--- a/clang/include/clang/Sema/Lookup.h
+++ b/clang/include/clang/Sema/Lookup.h
@@ -752,6 +752,10 @@ class LookupResult {
       IDNS &= ~Decl::IDNS_LocalExtern;
   }
 
+  void setNestedNameSpecifier(NestedNameSpecifier *Q) { Qualifier = Q; }
+
+  NestedNameSpecifier *getNestedNameSpecifier() const { return Qualifier; }
+
 private:
   void diagnoseAccess() {
     if (!isAmbiguous() && isClassLookup() &&
@@ -792,6 +796,7 @@ class LookupResult {
   CXXBasePaths *Paths = nullptr;
   CXXRecordDecl *NamingClass = nullptr;
   QualType BaseObjectType;
+  NestedNameSpecifier *Qualifier = nullptr;
 
   // Parameters.
   Sema *SemaPtr;
diff --git a/clang/lib/Sema/SemaAccess.cpp b/clang/lib/Sema/SemaAccess.cpp
index 4af3c0f30a8e8a..9077066da29d61 100644
--- a/clang/lib/Sema/SemaAccess.cpp
+++ b/clang/lib/Sema/SemaAccess.cpp
@@ -254,6 +254,9 @@ struct AccessTarget : public AccessedEntity {
       namingClass = cast<CXXRecordDecl>(namingClass->getParent());
     return namingClass->getCanonicalDecl();
   }
+  void setNestedNameSpecifier(NestedNameSpecifier *Q) { Qualifier = Q; }
+
+  NestedNameSpecifier *getNestedNameSpecifier() const { return Qualifier; }
 
 private:
   void initialize() {
@@ -274,6 +277,7 @@ struct AccessTarget : public AccessedEntity {
   mutable bool CalculatedInstanceContext : 1;
   mutable const CXXRecordDecl *InstanceContext;
   const CXXRecordDecl *DeclaringClass;
+  NestedNameSpecifier *Qualifier = nullptr;
 };
 
 }
@@ -1481,6 +1485,20 @@ static Sema::AccessResult CheckAccess(Sema &S, SourceLocation Loc,
   }
 
   EffectiveContext EC(S.CurContext);
+  if (Entity.getNestedNameSpecifier())
+    if (const Type *Ty = Entity.getNestedNameSpecifier()->getAsType())
+      switch (Ty->getTypeClass()) {
+      case Type::TypeClass::SubstTemplateTypeParm:
+        if (auto *SubstTemplateTy = Ty->getAs<SubstTemplateTypeParmType>())
+          if (auto *D = SubstTemplateTy->getAssociatedDecl())
+            if (auto *RD = dyn_cast_or_null<CXXRecordDecl>(D->getDeclContext()))
+              EC.Records.push_back(RD);
+
+        break;
+      default:
+        break;
+      }
+
   switch (CheckEffectiveAccess(S, EC, Loc, Entity)) {
   case AR_accessible: return Sema::AR_accessible;
   case AR_inaccessible: return Sema::AR_inaccessible;
@@ -1916,6 +1934,7 @@ void Sema::CheckLookupAccess(const LookupResult &R) {
       AccessTarget Entity(Context, AccessedEntity::Member,
                           R.getNamingClass(), I.getPair(),
                           R.getBaseObjectType());
+      Entity.setNestedNameSpecifier(R.getNestedNameSpecifier());
       Entity.setDiag(diag::err_access);
       CheckAccess(*this, R.getNameLoc(), Entity);
     }
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index a7910bda874c8d..d1555cfeb03e15 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -11275,6 +11275,7 @@ Sema::CheckTypenameType(ElaboratedTypeKeyword Keyword,
 
   DeclarationName Name(&II);
   LookupResult Result(*this, Name, IILoc, LookupOrdinaryName);
+  Result.setNestedNameSpecifier(QualifierLoc.getNestedNameSpecifier());
   if (Ctx)
     LookupQualifiedName(Result, Ctx, SS);
   else
diff --git a/clang/test/SemaTemplate/PR25708.cpp b/clang/test/SemaTemplate/PR25708.cpp
new file mode 100644
index 00000000000000..e9e96ebd015e04
--- /dev/null
+++ b/clang/test/SemaTemplate/PR25708.cpp
@@ -0,0 +1,23 @@
+// RUN: %clang_cc1 -std=c++11 -verify %s
+// RUN: %clang_cc1 -std=c++14 -verify %s
+// RUN: %clang_cc1 -std=c++17 -verify %s
+// RUN: %clang_cc1 -std=c++20 -verify=cxx20 %s
+// expected-no-diagnostics
+
+struct FooAccessor
+{
+    template <typename T>
+    using Foo = typename T::Foo;
+};
+
+class Type
+{
+    friend struct FooAccessor;
+    
+    using Foo = int;
+};
+
+int main()
+{
+    FooAccessor::Foo<Type> t;
+}
\ No newline at end of file

[jcsxky]

gently ping~

[erichkeane]

1 nit, else LGTM.

[erichkeane]

Unrelated change, please revert.

[jcsxky]

Fixed.

[zyn0217]

nit: This can be simplified using std::optional:

std::optional<ContextRAII> C;
if (!A.getDeclContext()->isFileContext())
  C.emplace(*this, A->getDeclContext());

[erichkeane]

nit: This can be simplified using std::optional:

std::optional<ContextRAII> C;
if (!A.getDeclContext()->isFileContext())
  C.emplace(*this, A->getDeclContext());

Neat trick, I like it!

[jcsxky]

Looks more clear. Thanks for your guidance!

[zyn0217]

Do we really need so many runs? I wonder if only -std=c++11 is sufficient.

[jcsxky]

Fixed.

[zyn0217]

I suspect this should have been placed under the group Bug Fixes to C++ Support...?

[jcsxky]

Updated and put it to the right place.