Add test for narrowing to unions of string literals

tests/baselines/reference/typeGuardNarrowsToLiteralTypeUnion.js

@@ -0,0 +1,21 @@
+//// [typeGuardNarrowsToLiteralTypeUnion.ts]
+declare function isFoo(value: string) : value is ("foo" | "bar");
+declare function doThis(value: "foo" | "bar"): void;
+declare function doThat(value: string) : void;
+let value: string;
+if (isFoo(value)) {
+    doThis(value);
+} else {
+    doThat(value);
+}
+
+
+
+//// [typeGuardNarrowsToLiteralTypeUnion.js]
+var value;
+if (isFoo(value)) {
+    doThis(value);
+}
+else {
+    doThat(value);
+}

tests/baselines/reference/typeGuardNarrowsToLiteralTypeUnion.symbols

@@ -0,0 +1,32 @@
+=== tests/cases/conformance/expressions/typeGuards/typeGuardNarrowsToLiteralTypeUnion.ts ===
+declare function isFoo(value: string) : value is ("foo" | "bar");
+>isFoo : Symbol(isFoo, Decl(typeGuardNarrowsToLiteralTypeUnion.ts, 0, 0))
+>value : Symbol(value, Decl(typeGuardNarrowsToLiteralTypeUnion.ts, 0, 23))
+>value : Symbol(value, Decl(typeGuardNarrowsToLiteralTypeUnion.ts, 0, 23))
+
+declare function doThis(value: "foo" | "bar"): void;
+>doThis : Symbol(doThis, Decl(typeGuardNarrowsToLiteralTypeUnion.ts, 0, 65))
+>value : Symbol(value, Decl(typeGuardNarrowsToLiteralTypeUnion.ts, 1, 24))
+
+declare function doThat(value: string) : void;
+>doThat : Symbol(doThat, Decl(typeGuardNarrowsToLiteralTypeUnion.ts, 1, 52))
+>value : Symbol(value, Decl(typeGuardNarrowsToLiteralTypeUnion.ts, 2, 24))
+
+let value: string;
+>value : Symbol(value, Decl(typeGuardNarrowsToLiteralTypeUnion.ts, 3, 3))
+
+if (isFoo(value)) {
+>isFoo : Symbol(isFoo, Decl(typeGuardNarrowsToLiteralTypeUnion.ts, 0, 0))
+>value : Symbol(value, Decl(typeGuardNarrowsToLiteralTypeUnion.ts, 3, 3))
+
+    doThis(value);
+>doThis : Symbol(doThis, Decl(typeGuardNarrowsToLiteralTypeUnion.ts, 0, 65))
+>value : Symbol(value, Decl(typeGuardNarrowsToLiteralTypeUnion.ts, 3, 3))
+
+} else {
+    doThat(value);
+>doThat : Symbol(doThat, Decl(typeGuardNarrowsToLiteralTypeUnion.ts, 1, 52))
+>value : Symbol(value, Decl(typeGuardNarrowsToLiteralTypeUnion.ts, 3, 3))
+}
+
+

tests/baselines/reference/typeGuardNarrowsToLiteralTypeUnion.types

@@ -0,0 +1,35 @@
+=== tests/cases/conformance/expressions/typeGuards/typeGuardNarrowsToLiteralTypeUnion.ts ===
+declare function isFoo(value: string) : value is ("foo" | "bar");
+>isFoo : (value: string) => value is "foo" | "bar"
+>value : string
+>value : any
+
+declare function doThis(value: "foo" | "bar"): void;
+>doThis : (value: "foo" | "bar") => void
+>value : "foo" | "bar"
+
+declare function doThat(value: string) : void;
+>doThat : (value: string) => void
+>value : string
+
+let value: string;
+>value : string
+
+if (isFoo(value)) {
+>isFoo(value) : boolean
+>isFoo : (value: string) => value is "foo" | "bar"
+>value : string
+
+    doThis(value);
+>doThis(value) : void
+>doThis : (value: "foo" | "bar") => void
+>value : "foo" | "bar"
+
+} else {
+    doThat(value);
+>doThat(value) : void
+>doThat : (value: string) => void
+>value : string
+}
+
+

tests/cases/conformance/expressions/typeGuards/typeGuardNarrowsToLiteralTypeUnion.ts

@@ -0,0 +1,10 @@
+declare function isFoo(value: string) : value is ("foo" | "bar");
+declare function doThis(value: "foo" | "bar"): void;
+declare function doThat(value: string) : void;
+let value: string;
+if (isFoo(value)) {
+    doThis(value);
+} else {
+    doThat(value);
+}
+