[ASTImporter] Fix ClassTemplateSpecialization in wrong DC

[martong]

Summary

ClassTemplateSpecialization is put in the wrong DeclContex if implicitly
instantiated. This patch fixes it.

[a.sidorin]

Hi Gabor! I have a question.

lib/AST/ASTImporter.cpp

4305

Can we write if (D2->isExplicitInstantiationOrSpecialization()) instead? How we should treat TSK_Undeclared case?

[a.sidorin]

(Sorry, accepted accidentially).

[martong]

Use isExplicitInstantiationOrSpecialization

[martong]

lib/AST/ASTImporter.cpp

4305

Yes, this is a good catch! Changed it.

[a.sidorin]

Hi Gabor,
Could you add a test for TSK_Undeclared as well?

[martong]

Could you add a test for TSK_Undeclared as well?

TLDR: No, I cannot.
TSK_Undeclared is used to indicate that a template specialization was formed from a template-id but has not yet been declared, defined, or instantiated.
Consequently, ClassTemplateSpecializationDecl::ClassTemplateSpecializationDecl and VarTemplateSpecializationDecl::VarTemplateSpecializationDecl initializes its member SpecializationKind to the value TSK_Undeclared.
SpecializationKind is getting set during parsing to a meaningful kind, it is never left as TSK_Undeclared.
So, the only way I could write a test is to manually change the SpecializationKind in the "From" context, but I consider that as not a meaningful test, since we cannot create such Decl by the parser.

[a.sidorin]

Ok, I got it, thank you!

lib/AST/ASTImporter.cpp

if (D2) {
     SourceLocation POI = Importer.Import(D->getPointOfInstantiation());
     if (POI.isValid())
       D2->setPointOfInstantiation(POI);
     else if (D->getPointOfInstantiation().isValid())
       return nullptr;
 
     D2->setTemplateSpecializationKind(D->getTemplateSpecializationKind());
 
-    // Add the specialization to this context.
+    // Set the context of this specialization/instantiation.
     D2->setLexicalDeclContext(LexicalDC);
+
+    // Add to the DC only if it was an explicit specialization/instantiation.
+    if (D2->getTemplateSpecializationKind() != TSK_ImplicitInstantiation) {
       LexicalDC->addDeclInternal(D2);
     }
+  }
   Importer.Imported(D, D2);
   if (D->isCompleteDefinition() && ImportDefinition(D, D2))
     return nullptr;
 
   return D2;
 }
 
 Decl *ASTNodeImporter::VisitVarTemplateDecl(VarTemplateDecl *D) {

unittests/AST/ASTImporterTest.cpp

TEST_P(ASTImporterTestBase, TUshouldNotContainTemplatedDeclOfTypeAlias) {
   };
 
   ASSERT_TRUE(Check(From));
   EXPECT_TRUE(Check(To));
 }
 
 TEST_P(
     ASTImporterTestBase,
-    DISABLED_TUshouldNotContainClassTemplateSpecializationOfImplicitInstantiation) {
+    TUshouldNotContainClassTemplateSpecializationOfImplicitInstantiation) {
 
   Decl *From, *To;
   std::tie(From, To) = getImportedDecl(
       R"(
       template<class T>
       class Base {};
       class declToImport : public Base<declToImport> {};
       )",