don't allow EvalWriteState without a provider

terraform/eval_state.go

@@ -212,6 +212,10 @@ func (n *EvalWriteState) Eval(ctx EvalContext) (interface{}, error) {
 	absAddr := n.Addr.Absolute(ctx.Path())
 	state := ctx.State()
 
+	if n.ProviderAddr.ProviderConfig.Type == "" {
+		return nil, fmt.Errorf("failed to write state for %s, missing provider type", absAddr)
+	}
+
 	obj := *n.State
 	if obj == nil || obj.Value.IsNull() {
 		// No need to encode anything: we'll just write it directly.