Argument dependent lookup with class argument is recursing into base classes that haven't been instantiated. This is generating an assertion in DeclTemplate.h. Fix for Bug25668.

[cryptoad]

This is an arc fail on my side

clang/lib/Sema/SemaLookup.cpp

AssociatedLookup(Sema &S, SourceLocation InstantiationLoc,
                      Sema::AssociatedNamespaceSet &Namespaces,
                      Sema::AssociatedClassSet &Classes)
       : S(S), Namespaces(Namespaces), Classes(Classes),
         InstantiationLoc(InstantiationLoc) {
     }
 
     bool addClassTransitive(CXXRecordDecl *RD) {
       Classes.insert(RD);
+      if (InstantiationLoc.isInvalid())
+        InstantiationLoc = RD->getLocation();
       return ClassesTransitive.insert(RD);
     }
 
     Sema &S;
     Sema::AssociatedNamespaceSet &Namespaces;
     Sema::AssociatedClassSet &Classes;
     SourceLocation InstantiationLoc;
 

clang/lib/Sema/SemaOpenMP.cpp

static void checkMappableExpressionList(
   // If the identifier of user-defined mapper is not specified, it is "default".
   // We do not change the actual name in this clause to distinguish whether a
   // mapper is specified explicitly, i.e., it is not explicitly specified when
   // MapperId.getName() is empty.
   if (!MapperId.getName() || MapperId.getName().isEmpty()) {
     auto &DeclNames = SemaRef.getASTContext().DeclarationNames;
     MapperId.setName(DeclNames.getIdentifier(
         &SemaRef.getASTContext().Idents.get("default")));
+    MapperId.setLoc(StartLoc);
   }
 
   // Iterators to find the current unresolved mapper expression.
   auto UMIt = UnresolvedMappers.begin(), UMEnd = UnresolvedMappers.end();
   bool UpdateUMIt = false;
   Expr *UnresolvedMapper = nullptr;
 
   // Keep track of the mappable components and base declarations in this clause.

clang/test/OpenMP/template-specialization.cpp

+// RUN: %clang_cc1 -verify -fopenmp -fsyntax-only %s
+
+// expected-no-diagnostics
+
+template <typename T>
+struct z {
+  static void aj() {
+    T f;
+#pragma omp target map(f)
+    ;
+  }
+};
+
+template <typename> class ar {};
+template <int> struct as {};
+template class z<ar<as<4>>>;