AST: Change isInvalid() on an accessor to delegate to the storage

This helps avoid a request cycle from the isInvalid() call inside
performAbstractFuncDeclDiagnostics().

Author: slavapestov

lib/AST/Decl.cpp

@@ -434,9 +434,15 @@ bool Decl::isInvalid() const {
   case DeclKind::Constructor:
   case DeclKind::Destructor:
   case DeclKind::Func:
-  case DeclKind::Accessor:
   case DeclKind::EnumElement:
     return cast<ValueDecl>(this)->getInterfaceType()->hasError();
+
+  case DeclKind::Accessor: {
+    auto *AD = cast<AccessorDecl>(this);
+    if (AD->hasInterfaceType() && AD->getInterfaceType()->hasError())
+      return true;
+    return AD->getStorage()->isInvalid();
+  }
   }
 
   llvm_unreachable("Unknown decl kind");