Add tests

tests/cases/conformance/types/union/unionTypeReduction2.ts

@@ -0,0 +1,66 @@
+// @strict: true
+
+function f1(x: { f(): void }, y: { f(x?: string): void }) {
+    let z = !!true ? x : y;  // { f(x?: string): void }
+    z.f();
+    z.f('hello');
+}
+
+function f2(x: { f(x: string | undefined): void }, y: { f(x?: string): void }) {
+    let z = !!true ? x : y;  // { f(x?: string): void }
+    z.f();
+    z.f('hello');
+}
+
+function f3(x: () => void, y: (x?: string) => void) {
+    let f = !!true ? x : y;  // (x?: string) => void
+    f();
+    f('hello');
+}
+
+function f4(x: (x: string | undefined) => void, y: (x?: string) => void) {
+    let f = !!true ? x : y;  // (x?: string) => void
+    f();
+    f('hello');
+}
+
+function f5(x: (x: string | undefined) => void, y: (x?: 'hello') => void) {
+    let f = !!true ? x : y;  // (x?: 'hello') => void
+    f();
+    f('hello');
+}
+
+function f6(x: (x: 'hello' | undefined) => void, y: (x?: string) => void) {
+    let f = !!true ? x : y;  // (x: 'hello' | undefined) => void
+    f();  // Error
+    f('hello');
+}
+
+type A = {
+    f(): void;
+}
+
+type B = {
+    f(x?: string): void;
+    g(): void;
+}
+
+function f11(a: A, b: B) {
+    let z = !!true ? a : b;  // A | B
+    z.f();
+    z.f('hello');
+}
+
+// Repro from #35414
+
+interface ReturnVal {
+    something(): void;
+}
+
+const k: ReturnVal = { something() { } }
+
+declare const val: ReturnVal;
+function run(options: { something?(b?: string): void }) {
+    const something = options.something ?? val.something;
+    something('');
+}