After an error of any kind has occurred, don't assert when attempting

to find the instantiated declaration within a template instantiation
fails to do so. It's likely that the original instantiation got
dropped due to instantiation failures, which doesn't actually break
the invariants of the AST. This eliminates a number of
crash-on-invalid failures, e.g., PR9300.

llvm-svn: 127030

clang/lib/Sema/SemaTemplateInstantiateDecl.cpp

@@ -3031,9 +3031,11 @@ NamedDecl *Sema::FindInstantiatedDecl(SourceLocation Loc, NamedDecl *D,
     }
 
     // UsingShadowDecls can instantiate to nothing because of using hiding.
-    assert((Result || isa<UsingShadowDecl>(D) || D->isInvalidDecl() ||
-            cast<Decl>(ParentDC)->isInvalidDecl())
-           && "Unable to find instantiation of declaration!");
+    // Note: this assertion end up firing in invalid code even when none of the 
+    // AST invariants have been broken, so we explicitly check whether any
+    // errors have been emitted
+    assert((Result || isa<UsingShadowDecl>(D) || Diags.hasErrorOccurred()) &&
+           "Unable to find instantiation of declaration!");
 
     D = Result;
   }