Added test.

Author: DanielRosenwasser

tests/cases/compiler/errorsWithCallablesInUnions01.ts

@@ -0,0 +1,10 @@
+interface IDirectiveLinkFn<TScope> {
+    (scope: TScope): void;
+}
+
+interface IDirectivePrePost<TScope> {
+    pre?: IDirectiveLinkFn<TScope>;
+    post?: IDirectiveLinkFn<TScope>;
+}
+
+export let blah: IDirectiveLinkFn<number> | IDirectivePrePost<number> = (x: string) => {}