Add tests

Author: ahejlsberg

tests/cases/conformance/types/union/discriminatedUnionTypes2.ts

@@ -0,0 +1,74 @@
+// @strict: true
+
+function f10(x : { kind: false, a: string } | { kind: true, b: string } | { kind: string, c: string }) {
+    if (x.kind === false) {
+        x.a;
+    }
+    else if (x.kind === true) {
+        x.b;
+    }
+    else {
+        x.c;
+    }
+}
+
+function f11(x : { kind: false, a: string } | { kind: true, b: string } | { kind: string, c: string }) {
+    switch (x.kind) {
+        case false:
+            x.a;
+            break;
+        case true:
+            x.b;
+            break;
+        default:
+            x.c;
+    }
+}
+
+function f13(x: { a: null; b: string } | { a: string, c: number }) {
+    x = { a: null, b: "foo", c: 4};  // Error
+}
+
+function f14<T>(x: { a: 0; b: string } | { a: T, c: number }) {
+    if (x.a === 0) {
+        x.b;  // Error
+    }
+}
+
+type Result<T> = { error?: undefined, value: T } | { error: Error };
+
+function f15(x: Result<number>) {
+    if (!x.error) {
+        x.value;
+    }
+    else {
+        x.error.message;
+    }
+}
+
+f15({ value: 10 });
+f15({ error: new Error("boom") });
+
+// Repro from #24193
+
+interface WithError {
+    error: Error
+    data: null
+}
+
+interface WithoutError<Data> {
+    error: null
+    data: Data
+}
+
+type DataCarrier<Data> = WithError | WithoutError<Data>
+
+function f20<Data>(carrier: DataCarrier<Data>) {
+    if (carrier.error === null) {
+        const error: null = carrier.error
+        const data: Data = carrier.data
+    } else {
+        const error: Error = carrier.error
+        const data: null = carrier.data
+    }
+}