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take mapper into consideration when validating conditional type
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@gabritto
gabritto committed Oct 7, 2024
1 parent 228148d commit 76718d8
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Showing 5 changed files with 400 additions and 165 deletions.
25 changes: 19 additions & 6 deletions src/compiler/checker.ts
View file
Original file line number Diff line number Diff line change
Expand Up @@ -2370,7 +2370,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
[".json", ".json"],
];

var narrowableReturnTypeCache = new Map<TypeId, boolean>();
var narrowableReturnTypeCache = new Map<string, boolean>();
/* eslint-enable no-var */

initializeTypeChecker();
Expand Down Expand Up @@ -20306,7 +20306,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
const checkType = root.checkType;
let distributionType = root.isDistributive ? getReducedType(getMappedType(checkType, newMapper)) : undefined;
let narrowingBaseType: Type | undefined;
const forNarrowing = distributionType && isNarrowingSubstitutionType(distributionType) && isNarrowableConditionalTypeWorker(type);
const forNarrowing = distributionType && isNarrowingSubstitutionType(distributionType) && isNarrowableConditionalType(type, mapper);
if (forNarrowing) {
narrowingBaseType = (distributionType as SubstitutionType).baseType;
distributionType = getReducedType((distributionType as SubstitutionType).constraint);
Expand Down Expand Up @@ -45868,11 +45868,23 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
: !!(returnType.indexType.flags & TypeFlags.TypeParameter);
}

function isNarrowableConditionalType(type: ConditionalType): boolean {
let result = narrowableReturnTypeCache.get(type.id);
function isNarrowableConditionalType(type: ConditionalType, mapper?: TypeMapper): boolean {
const typeArguments = mapper && map(type.root.outerTypeParameters, t => {
const mapped = getMappedType(t, mapper);
if (isNarrowingSubstitutionType(mapped)) {
return (mapped as SubstitutionType).baseType;
}
return mapped;
});
const id = `${type.id}:${getTypeListId(typeArguments)}`;
let result = narrowableReturnTypeCache.get(id);
if (result === undefined) {
result = isNarrowableConditionalTypeWorker(type);
narrowableReturnTypeCache.set(type.id, result);
const nonNarrowingMapper = type.root.outerTypeParameters
&& typeArguments
&& createTypeMapper(type.root.outerTypeParameters, typeArguments);
const instantiatedType = instantiateType(type, nonNarrowingMapper);
result = isConditionalType(instantiatedType) && isNarrowableConditionalTypeWorker(instantiatedType);
narrowableReturnTypeCache.set(id, result);
}
return result;
}
Expand Down Expand Up @@ -45905,6 +45917,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
if (!constraintType || !(constraintType.flags & TypeFlags.Union)) {
return false;
}

// (3)
if (
!everyType(type.extendsType, extendsType =>
Expand Down
82 changes: 58 additions & 24 deletions tests/baselines/reference/dependentReturnType6.errors.txt
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Original file line number Diff line number Diff line change
@@ -1,25 +1,27 @@
file.ts(26,26): error TS2322: Type 'true' is not assignable to type 'SomeInterface<T>[U]'.
file.ts(28,26): error TS2322: Type 'true' is not assignable to type 'SomeInterfaceBad<T>[U]'.
Type 'true' is not assignable to type 'T extends 1 ? true : T extends 2 ? false : never'.
file.ts(26,33): error TS2322: Type 'false' is not assignable to type 'SomeInterface<T>[U]'.
file.ts(28,33): error TS2322: Type 'false' is not assignable to type 'SomeInterfaceBad<T>[U]'.
Type 'false' is not assignable to type 'T extends 1 ? true : T extends 2 ? false : never'.
file.ts(28,16): error TS2322: Type '1' is not assignable to type 'SomeInterface<T>[U]'.
file.ts(30,16): error TS2322: Type '1' is not assignable to type 'SomeInterfaceBad<T>[U]'.
Type '1' is not assignable to type 'T extends true ? 1 : T extends false ? 2 : never'.
file.ts(28,20): error TS2322: Type '2' is not assignable to type 'SomeInterface<T>[U]'.
file.ts(30,20): error TS2322: Type '2' is not assignable to type 'SomeInterfaceBad<T>[U]'.
Type '2' is not assignable to type 'T extends true ? 1 : T extends false ? 2 : never'.
file.ts(65,13): error TS2322: Type '1' is not assignable to type 'this extends Sub1 ? 1 : this extends Sub2 ? 2 : never'.
file.ts(67,9): error TS2322: Type '2' is not assignable to type 'this extends Sub1 ? 1 : this extends Sub2 ? 2 : never'.
file.ts(79,16): error TS2322: Type '1' is not assignable to type 'T extends true ? 1 : T extends false ? 2 : never'.
file.ts(79,20): error TS2322: Type '2' is not assignable to type 'T extends true ? 1 : T extends false ? 2 : never'.
file.ts(83,100): error TS2322: Type '1 | 2' is not assignable to type 'T extends true ? 1 : T extends false ? 2 : never'.
file.ts(80,13): error TS2322: Type '1' is not assignable to type 'this extends Sub1 ? 1 : this extends Sub2 ? 2 : never'.
file.ts(82,9): error TS2322: Type '2' is not assignable to type 'this extends Sub1 ? 1 : this extends Sub2 ? 2 : never'.
file.ts(94,16): error TS2322: Type '1' is not assignable to type 'T extends true ? 1 : T extends false ? 2 : never'.
file.ts(94,20): error TS2322: Type '2' is not assignable to type 'T extends true ? 1 : T extends false ? 2 : never'.
file.ts(98,100): error TS2322: Type '1 | 2' is not assignable to type 'T extends true ? 1 : T extends false ? 2 : never'.
Type '1' is not assignable to type 'T extends true ? 1 : T extends false ? 2 : never'.
file.ts(91,9): error TS2322: Type 'number' is not assignable to type 'SomeCond<T>'.
file.ts(91,9): error TS2589: Type instantiation is excessively deep and possibly infinite.
file.ts(93,5): error TS2322: Type 'number' is not assignable to type 'SomeCond<T>'.
file.ts(99,60): error TS2366: Function lacks ending return statement and return type does not include 'undefined'.
file.ts(101,9): error TS2322: Type '"one"' is not assignable to type 'OtherCond<U> | OtherCond<V>'.
file.ts(106,9): error TS2322: Type 'number' is not assignable to type 'SomeCond<T>'.
file.ts(106,9): error TS2589: Type instantiation is excessively deep and possibly infinite.
file.ts(108,5): error TS2322: Type 'number' is not assignable to type 'SomeCond<T>'.
file.ts(114,60): error TS2366: Function lacks ending return statement and return type does not include 'undefined'.
file.ts(116,9): error TS2322: Type '"one"' is not assignable to type 'OtherCond<U> | OtherCond<V>'.
file.ts(126,9): error TS2322: Type '"a"' is not assignable to type 'T extends (infer P)[] ? P : T extends number ? undefined : never'.
file.ts(128,5): error TS2322: Type 'undefined' is not assignable to type 'T extends (infer P)[] ? P : T extends number ? undefined : never'.


==== file.ts (14 errors) ====
==== file.ts (16 errors) ====
// Type parameter in outer scope
function outer<T extends boolean>(x: T): number {
return inner();
Expand All @@ -37,31 +39,46 @@ file.ts(101,9): error TS2322: Type '"one"' is not assignable to type 'OtherCond<
return x ? y !== undefined ? y : 1 : 2;
}

// Indexed access with conditional inside - DOESN'T NARROW the nested conditional type
interface SomeInterface<T> {
// Indexed access with conditional inside

// DOESN'T NARROW the nested conditional type of wrong shape
interface SomeInterfaceBad<T> {
prop1: T extends 1 ? true : T extends 2 ? false : never;
prop2: T extends true ? 1 : T extends false ? 2 : never;
}

function fun4<T, U extends keyof SomeInterface<unknown>>(x: T, y: U): SomeInterface<T>[U] {
function fun4bad<T, U extends keyof SomeInterfaceBad<unknown>>(x: T, y: U): SomeInterfaceBad<T>[U] {
if (y === "prop1") {
return x === 1 ? true : false;
~~~~
!!! error TS2322: Type 'true' is not assignable to type 'SomeInterface<T>[U]'.
!!! error TS2322: Type 'true' is not assignable to type 'SomeInterfaceBad<T>[U]'.
!!! error TS2322: Type 'true' is not assignable to type 'T extends 1 ? true : T extends 2 ? false : never'.
~~~~~
!!! error TS2322: Type 'false' is not assignable to type 'SomeInterface<T>[U]'.
!!! error TS2322: Type 'false' is not assignable to type 'SomeInterfaceBad<T>[U]'.
!!! error TS2322: Type 'false' is not assignable to type 'T extends 1 ? true : T extends 2 ? false : never'.
}
return x ? 1 : 2;
~
!!! error TS2322: Type '1' is not assignable to type 'SomeInterface<T>[U]'.
!!! error TS2322: Type '1' is not assignable to type 'SomeInterfaceBad<T>[U]'.
!!! error TS2322: Type '1' is not assignable to type 'T extends true ? 1 : T extends false ? 2 : never'.
~
!!! error TS2322: Type '2' is not assignable to type 'SomeInterface<T>[U]'.
!!! error TS2322: Type '2' is not assignable to type 'SomeInterfaceBad<T>[U]'.
!!! error TS2322: Type '2' is not assignable to type 'T extends true ? 1 : T extends false ? 2 : never'.
}

// Narrows nested conditional type of right shape
interface SomeInterfaceGood<T> {
prop1: T extends true ? 2 : T extends false ? 1 : never;
prop2: T extends true ? 1 : T extends false ? 2 : never;
}

function fun4good<T extends boolean, U extends keyof SomeInterfaceGood<unknown>>(x: T, y: U): SomeInterfaceGood<T>[U] {
if (y === "prop1") {
return x ? 2 : 1;
}
return x ? 1 : 2;
}

// Indexed access with indexed access inside - OK, narrows
interface BB {
"a": number;
Expand Down Expand Up @@ -126,7 +143,7 @@ file.ts(101,9): error TS2322: Type '"one"' is not assignable to type 'OtherCond<
~~~~~~~~~
!!! error TS2322: Type '1 | 2' is not assignable to type 'T extends true ? 1 : T extends false ? 2 : never'.
!!! error TS2322: Type '1' is not assignable to type 'T extends true ? 1 : T extends false ? 2 : never'.
!!! related TS6502 file.ts:83:13: The expected type comes from the return type of this signature.
!!! related TS6502 file.ts:98:13: The expected type comes from the return type of this signature.


// Circular conditionals
Expand Down Expand Up @@ -156,4 +173,21 @@ file.ts(101,9): error TS2322: Type '"one"' is not assignable to type 'OtherCond<
~~~~~~
!!! error TS2322: Type '"one"' is not assignable to type 'OtherCond<U> | OtherCond<V>'.
}
}
}

// Conditionals with `infer` - will not narrow, it is not safe to infer from the narrowed type into an `infer` type parameter
function f9<T extends "a"[] | "b"[] | number>(x: T): T extends Array<infer P> ? P : T extends number ? undefined : never {
if (Array.isArray(x)) {
// If we allowed narrowing of the conditional return type, when resolving the conditional `T & ("a"[] | "b"[]) extends Array<infer P> ? P : ...`,
// we could infer `"a" | "b"` for `P`, and allow "a" to be returned. However, when calling `f10`, `T` could be instantiated with `"b"[]`, and the return type would be `"b"`,
// so allowing an `"a"` return would be unsound.
return "a";
~~~~~~
!!! error TS2322: Type '"a"' is not assignable to type 'T extends (infer P)[] ? P : T extends number ? undefined : never'.
}
return undefined;
~~~~~~
!!! error TS2322: Type 'undefined' is not assignable to type 'T extends (infer P)[] ? P : T extends number ? undefined : never'.
}


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