Add test for intersection narrowing bug (#45296)

tests/baselines/reference/narrowingIntersection.js

@@ -0,0 +1,40 @@
+//// [narrowingIntersection.ts]
+// Somehow this being an intersection matters.
+type FooAndBaz = { foo: unknown } & { baz: unknown };
+
+type Disjoint =
+ | { readonly value: string; readonly err?: never; }
+ | { readonly value?: never; readonly err: FooAndBaz; };
+
+function test1(result: Disjoint): string {
+    if (result.err) {
+        throw result.err;
+    }
+    // Error, should OK
+    return result.value;
+}
+
+type TrivialIntersection = { a: 1 } & { a: 1 };
+
+function want0(x: 0) {}
+
+function test2(a: 0 | TrivialIntersection) {
+    if (a === 0) {
+        want0(a); // Fails, but expect to work
+    }
+}
+
+//// [narrowingIntersection.js]
+function test1(result) {
+    if (result.err) {
+        throw result.err;
+    }
+    // Error, should OK
+    return result.value;
+}
+function want0(x) { }
+function test2(a) {
+    if (a === 0) {
+        want0(a); // Fails, but expect to work
+    }
+}

tests/baselines/reference/narrowingIntersection.symbols

@@ -0,0 +1,63 @@
+=== tests/cases/compiler/narrowingIntersection.ts ===
+// Somehow this being an intersection matters.
+type FooAndBaz = { foo: unknown } & { baz: unknown };
+>FooAndBaz : Symbol(FooAndBaz, Decl(narrowingIntersection.ts, 0, 0))
+>foo : Symbol(foo, Decl(narrowingIntersection.ts, 1, 18))
+>baz : Symbol(baz, Decl(narrowingIntersection.ts, 1, 37))
+
+type Disjoint =
+>Disjoint : Symbol(Disjoint, Decl(narrowingIntersection.ts, 1, 53))
+
+ | { readonly value: string; readonly err?: never; }
+>value : Symbol(value, Decl(narrowingIntersection.ts, 4, 4))
+>err : Symbol(err, Decl(narrowingIntersection.ts, 4, 28))
+
+ | { readonly value?: never; readonly err: FooAndBaz; };
+>value : Symbol(value, Decl(narrowingIntersection.ts, 5, 4))
+>err : Symbol(err, Decl(narrowingIntersection.ts, 5, 28))
+>FooAndBaz : Symbol(FooAndBaz, Decl(narrowingIntersection.ts, 0, 0))
+
+function test1(result: Disjoint): string {
+>test1 : Symbol(test1, Decl(narrowingIntersection.ts, 5, 56))
+>result : Symbol(result, Decl(narrowingIntersection.ts, 7, 15))
+>Disjoint : Symbol(Disjoint, Decl(narrowingIntersection.ts, 1, 53))
+
+    if (result.err) {
+>result.err : Symbol(err, Decl(narrowingIntersection.ts, 4, 28), Decl(narrowingIntersection.ts, 5, 28))
+>result : Symbol(result, Decl(narrowingIntersection.ts, 7, 15))
+>err : Symbol(err, Decl(narrowingIntersection.ts, 4, 28), Decl(narrowingIntersection.ts, 5, 28))
+
+        throw result.err;
+>result.err : Symbol(err, Decl(narrowingIntersection.ts, 4, 28), Decl(narrowingIntersection.ts, 5, 28))
+>result : Symbol(result, Decl(narrowingIntersection.ts, 7, 15))
+>err : Symbol(err, Decl(narrowingIntersection.ts, 4, 28), Decl(narrowingIntersection.ts, 5, 28))
+    }
+    // Error, should OK
+    return result.value;
+>result.value : Symbol(value, Decl(narrowingIntersection.ts, 4, 4), Decl(narrowingIntersection.ts, 5, 4))
+>result : Symbol(result, Decl(narrowingIntersection.ts, 7, 15))
+>value : Symbol(value, Decl(narrowingIntersection.ts, 4, 4), Decl(narrowingIntersection.ts, 5, 4))
+}
+
+type TrivialIntersection = { a: 1 } & { a: 1 };
+>TrivialIntersection : Symbol(TrivialIntersection, Decl(narrowingIntersection.ts, 13, 1))
+>a : Symbol(a, Decl(narrowingIntersection.ts, 15, 28))
+>a : Symbol(a, Decl(narrowingIntersection.ts, 15, 39))
+
+function want0(x: 0) {}
+>want0 : Symbol(want0, Decl(narrowingIntersection.ts, 15, 47))
+>x : Symbol(x, Decl(narrowingIntersection.ts, 17, 15))
+
+function test2(a: 0 | TrivialIntersection) {
+>test2 : Symbol(test2, Decl(narrowingIntersection.ts, 17, 23))
+>a : Symbol(a, Decl(narrowingIntersection.ts, 19, 15))
+>TrivialIntersection : Symbol(TrivialIntersection, Decl(narrowingIntersection.ts, 13, 1))
+
+    if (a === 0) {
+>a : Symbol(a, Decl(narrowingIntersection.ts, 19, 15))
+
+        want0(a); // Fails, but expect to work
+>want0 : Symbol(want0, Decl(narrowingIntersection.ts, 15, 47))
+>a : Symbol(a, Decl(narrowingIntersection.ts, 19, 15))
+    }
+}

tests/baselines/reference/narrowingIntersection.types

@@ -0,0 +1,63 @@
+=== tests/cases/compiler/narrowingIntersection.ts ===
+// Somehow this being an intersection matters.
+type FooAndBaz = { foo: unknown } & { baz: unknown };
+>FooAndBaz : FooAndBaz
+>foo : unknown
+>baz : unknown
+
+type Disjoint =
+>Disjoint : Disjoint
+
+ | { readonly value: string; readonly err?: never; }
+>value : string
+>err : never
+
+ | { readonly value?: never; readonly err: FooAndBaz; };
+>value : never
+>err : FooAndBaz
+
+function test1(result: Disjoint): string {
+>test1 : (result: Disjoint) => string
+>result : Disjoint
+
+    if (result.err) {
+>result.err : FooAndBaz
+>result : Disjoint
+>err : FooAndBaz
+
+        throw result.err;
+>result.err : FooAndBaz
+>result : Disjoint
+>err : FooAndBaz
+    }
+    // Error, should OK
+    return result.value;
+>result.value : string
+>result : Disjoint
+>value : string
+}
+
+type TrivialIntersection = { a: 1 } & { a: 1 };
+>TrivialIntersection : TrivialIntersection
+>a : 1
+>a : 1
+
+function want0(x: 0) {}
+>want0 : (x: 0) => void
+>x : 0
+
+function test2(a: 0 | TrivialIntersection) {
+>test2 : (a: 0 | TrivialIntersection) => void
+>a : 0 | TrivialIntersection
+
+    if (a === 0) {
+>a === 0 : boolean
+>a : 0 | TrivialIntersection
+>0 : 0
+
+        want0(a); // Fails, but expect to work
+>want0(a) : void
+>want0 : (x: 0) => void
+>a : 0
+    }
+}

tests/cases/compiler/narrowingIntersection.ts

@@ -0,0 +1,24 @@
+// Somehow this being an intersection matters.
+type FooAndBaz = { foo: unknown } & { baz: unknown };
+
+type Disjoint =
+ | { readonly value: string; readonly err?: never; }
+ | { readonly value?: never; readonly err: FooAndBaz; };
+
+function test1(result: Disjoint): string {
+    if (result.err) {
+        throw result.err;
+    }
+    // Error, should OK
+    return result.value;
+}
+
+type TrivialIntersection = { a: 1 } & { a: 1 };
+
+function want0(x: 0) {}
+
+function test2(a: 0 | TrivialIntersection) {
+    if (a === 0) {
+        want0(a); // Fails, but expect to work
+    }
+}