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Use comparability for discriminant properties when narrowing types for a default switch clause #61211

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Merged
merged 3 commits into from
Oct 30, 2025
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Merged

Use comparability for discriminant properties when narrowing types for a default switch clause #61211

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0baf4d5
Use comparability for discriminant properties when narrowing types fo…
Andarist Feb 18, 2025
69aeca4
Merge branch 'main' into fix/narrow-type-by-switch-on-discriminant
Andarist Oct 29, 2025
7a7fad2
Merge branch 'main' into fix/narrow-type-by-switch-on-discriminant
Andarist Oct 30, 2025
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2 changes: 1 addition & 1 deletion src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -29739,7 +29739,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
if (!hasDefaultClause) {
return caseType;
}
const defaultType = filterType(type, t => !(isUnitLikeType(t) && contains(switchTypes, t.flags & TypeFlags.Undefined ? undefinedType : getRegularTypeOfLiteralType(extractUnitType(t)))));
const defaultType = filterType(type, t => !(isUnitLikeType(t) && contains(switchTypes, t.flags & TypeFlags.Undefined ? undefinedType : getRegularTypeOfLiteralType(extractUnitType(t)), (t1, t2) => isUnitType(t1) && areTypesComparable(t1, t2))));
return caseType.flags & TypeFlags.Never ? defaultType : getUnionType([caseType, defaultType]);
}

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180 changes: 180 additions & 0 deletions tests/baselines/reference/discriminatedUnionTypes4.symbols
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@@ -0,0 +1,180 @@
//// [tests/cases/conformance/types/union/discriminatedUnionTypes4.ts] ////

=== discriminatedUnionTypes4.ts ===
// https://github.com/microsoft/TypeScript/issues/61207

enum AnimalType {
>AnimalType : Symbol(AnimalType, Decl(discriminatedUnionTypes4.ts, 0, 0))

cat = "cat",
>cat : Symbol(AnimalType.cat, Decl(discriminatedUnionTypes4.ts, 2, 17))

dog = "dog",
>dog : Symbol(AnimalType.dog, Decl(discriminatedUnionTypes4.ts, 3, 14))
}

type Animal =
>Animal : Symbol(Animal, Decl(discriminatedUnionTypes4.ts, 5, 1))

| {
type: `${AnimalType.cat}`;
>type : Symbol(type, Decl(discriminatedUnionTypes4.ts, 8, 5))
>AnimalType : Symbol(AnimalType, Decl(discriminatedUnionTypes4.ts, 0, 0))
>cat : Symbol(AnimalType.cat, Decl(discriminatedUnionTypes4.ts, 2, 17))

meow: string;
>meow : Symbol(meow, Decl(discriminatedUnionTypes4.ts, 9, 32))
}
| {
type: `${AnimalType.dog}`;
>type : Symbol(type, Decl(discriminatedUnionTypes4.ts, 12, 5))
>AnimalType : Symbol(AnimalType, Decl(discriminatedUnionTypes4.ts, 0, 0))
>dog : Symbol(AnimalType.dog, Decl(discriminatedUnionTypes4.ts, 3, 14))

bark: string;
>bark : Symbol(bark, Decl(discriminatedUnionTypes4.ts, 13, 32))

};

function check(p: never) {
>check : Symbol(check, Decl(discriminatedUnionTypes4.ts, 15, 6))
>p : Symbol(p, Decl(discriminatedUnionTypes4.ts, 17, 15))

throw new Error("Error!");
>Error : Symbol(Error, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
}

function action1(animal: Animal) {
>action1 : Symbol(action1, Decl(discriminatedUnionTypes4.ts, 19, 1))
>animal : Symbol(animal, Decl(discriminatedUnionTypes4.ts, 21, 17))
>Animal : Symbol(Animal, Decl(discriminatedUnionTypes4.ts, 5, 1))

if (animal.type === AnimalType.cat) {
>animal.type : Symbol(type, Decl(discriminatedUnionTypes4.ts, 8, 5), Decl(discriminatedUnionTypes4.ts, 12, 5))
>animal : Symbol(animal, Decl(discriminatedUnionTypes4.ts, 21, 17))
>type : Symbol(type, Decl(discriminatedUnionTypes4.ts, 8, 5), Decl(discriminatedUnionTypes4.ts, 12, 5))
>AnimalType.cat : Symbol(AnimalType.cat, Decl(discriminatedUnionTypes4.ts, 2, 17))
>AnimalType : Symbol(AnimalType, Decl(discriminatedUnionTypes4.ts, 0, 0))
>cat : Symbol(AnimalType.cat, Decl(discriminatedUnionTypes4.ts, 2, 17))

console.log(animal.meow);
>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
>animal.meow : Symbol(meow, Decl(discriminatedUnionTypes4.ts, 9, 32))
>animal : Symbol(animal, Decl(discriminatedUnionTypes4.ts, 21, 17))
>meow : Symbol(meow, Decl(discriminatedUnionTypes4.ts, 9, 32))

} else if (animal.type === AnimalType.dog) {
>animal.type : Symbol(type, Decl(discriminatedUnionTypes4.ts, 12, 5))
>animal : Symbol(animal, Decl(discriminatedUnionTypes4.ts, 21, 17))
>type : Symbol(type, Decl(discriminatedUnionTypes4.ts, 12, 5))
>AnimalType.dog : Symbol(AnimalType.dog, Decl(discriminatedUnionTypes4.ts, 3, 14))
>AnimalType : Symbol(AnimalType, Decl(discriminatedUnionTypes4.ts, 0, 0))
>dog : Symbol(AnimalType.dog, Decl(discriminatedUnionTypes4.ts, 3, 14))

console.log(animal.bark);
>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
>animal.bark : Symbol(bark, Decl(discriminatedUnionTypes4.ts, 13, 32))
>animal : Symbol(animal, Decl(discriminatedUnionTypes4.ts, 21, 17))
>bark : Symbol(bark, Decl(discriminatedUnionTypes4.ts, 13, 32))

} else {
check(animal);
>check : Symbol(check, Decl(discriminatedUnionTypes4.ts, 15, 6))
>animal : Symbol(animal, Decl(discriminatedUnionTypes4.ts, 21, 17))
}
}

function action2(animal: Animal) {
>action2 : Symbol(action2, Decl(discriminatedUnionTypes4.ts, 29, 1))
>animal : Symbol(animal, Decl(discriminatedUnionTypes4.ts, 31, 17))
>Animal : Symbol(Animal, Decl(discriminatedUnionTypes4.ts, 5, 1))

switch (animal.type) {
>animal.type : Symbol(type, Decl(discriminatedUnionTypes4.ts, 8, 5), Decl(discriminatedUnionTypes4.ts, 12, 5))
>animal : Symbol(animal, Decl(discriminatedUnionTypes4.ts, 31, 17))
>type : Symbol(type, Decl(discriminatedUnionTypes4.ts, 8, 5), Decl(discriminatedUnionTypes4.ts, 12, 5))

case `${AnimalType.cat}`:
>AnimalType.cat : Symbol(AnimalType.cat, Decl(discriminatedUnionTypes4.ts, 2, 17))
>AnimalType : Symbol(AnimalType, Decl(discriminatedUnionTypes4.ts, 0, 0))
>cat : Symbol(AnimalType.cat, Decl(discriminatedUnionTypes4.ts, 2, 17))

console.log(animal.meow);
>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
>animal.meow : Symbol(meow, Decl(discriminatedUnionTypes4.ts, 9, 32))
>animal : Symbol(animal, Decl(discriminatedUnionTypes4.ts, 31, 17))
>meow : Symbol(meow, Decl(discriminatedUnionTypes4.ts, 9, 32))

break;
case `${AnimalType.dog}`:
>AnimalType.dog : Symbol(AnimalType.dog, Decl(discriminatedUnionTypes4.ts, 3, 14))
>AnimalType : Symbol(AnimalType, Decl(discriminatedUnionTypes4.ts, 0, 0))
>dog : Symbol(AnimalType.dog, Decl(discriminatedUnionTypes4.ts, 3, 14))

console.log(animal.bark);
>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
>animal.bark : Symbol(bark, Decl(discriminatedUnionTypes4.ts, 13, 32))
>animal : Symbol(animal, Decl(discriminatedUnionTypes4.ts, 31, 17))
>bark : Symbol(bark, Decl(discriminatedUnionTypes4.ts, 13, 32))

break;
default:
check(animal);
>check : Symbol(check, Decl(discriminatedUnionTypes4.ts, 15, 6))
>animal : Symbol(animal, Decl(discriminatedUnionTypes4.ts, 31, 17))
}
}

function action3(animal: Animal) {
>action3 : Symbol(action3, Decl(discriminatedUnionTypes4.ts, 42, 1))
>animal : Symbol(animal, Decl(discriminatedUnionTypes4.ts, 44, 17))
>Animal : Symbol(Animal, Decl(discriminatedUnionTypes4.ts, 5, 1))

switch (animal.type) {
>animal.type : Symbol(type, Decl(discriminatedUnionTypes4.ts, 8, 5), Decl(discriminatedUnionTypes4.ts, 12, 5))
>animal : Symbol(animal, Decl(discriminatedUnionTypes4.ts, 44, 17))
>type : Symbol(type, Decl(discriminatedUnionTypes4.ts, 8, 5), Decl(discriminatedUnionTypes4.ts, 12, 5))

case AnimalType.cat:
>AnimalType.cat : Symbol(AnimalType.cat, Decl(discriminatedUnionTypes4.ts, 2, 17))
>AnimalType : Symbol(AnimalType, Decl(discriminatedUnionTypes4.ts, 0, 0))
>cat : Symbol(AnimalType.cat, Decl(discriminatedUnionTypes4.ts, 2, 17))

console.log(animal.meow);
>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
>animal.meow : Symbol(meow, Decl(discriminatedUnionTypes4.ts, 9, 32))
>animal : Symbol(animal, Decl(discriminatedUnionTypes4.ts, 44, 17))
>meow : Symbol(meow, Decl(discriminatedUnionTypes4.ts, 9, 32))

break;
case AnimalType.dog:
>AnimalType.dog : Symbol(AnimalType.dog, Decl(discriminatedUnionTypes4.ts, 3, 14))
>AnimalType : Symbol(AnimalType, Decl(discriminatedUnionTypes4.ts, 0, 0))
>dog : Symbol(AnimalType.dog, Decl(discriminatedUnionTypes4.ts, 3, 14))

console.log(animal.bark);
>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
>animal.bark : Symbol(bark, Decl(discriminatedUnionTypes4.ts, 13, 32))
>animal : Symbol(animal, Decl(discriminatedUnionTypes4.ts, 44, 17))
>bark : Symbol(bark, Decl(discriminatedUnionTypes4.ts, 13, 32))

break;
default:
check(animal);
>check : Symbol(check, Decl(discriminatedUnionTypes4.ts, 15, 6))
>animal : Symbol(animal, Decl(discriminatedUnionTypes4.ts, 44, 17))
}
}

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