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Improve isTypeParameterAtTopLevel to handle substitution types and template literal types #60643

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Improve isTypeParameterAtTopLevel to handle substitution types and template literal types #60643

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Improve `isTypeParameterAtTopLevel` to handle substitution types and …
Andarist Nov 30, 2024
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Andarist Nov 30, 2024
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7 changes: 5 additions & 2 deletions src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -25741,12 +25741,15 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
}

function isTypeParameterAtTopLevel(type: Type, tp: TypeParameter, depth = 0): boolean {
if (type.flags & TypeFlags.Substitution) {
type = getActualTypeVariable(type);
}
return !!(type === tp ||
type.flags & TypeFlags.UnionOrIntersection && some((type as UnionOrIntersectionType).types, t => isTypeParameterAtTopLevel(t, tp, depth)) ||
depth < 3 && type.flags & TypeFlags.Conditional && (
depth < 3 && (type.flags & TypeFlags.Conditional && (
isTypeParameterAtTopLevel(getTrueTypeFromConditionalType(type as ConditionalType), tp, depth + 1) ||
isTypeParameterAtTopLevel(getFalseTypeFromConditionalType(type as ConditionalType), tp, depth + 1)
));
) || type.flags & TypeFlags.TemplateLiteral && some((type as TemplateLiteralType).types, t => isTypeParameterAtTopLevel(t, tp, depth))));
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TODO: handle TypeFlags.StringMapping too if this part of the PR turns out to be seen as a positive change too

}

function isTypeParameterAtTopLevelInReturnType(signature: Signature, typeParameter: TypeParameter) {
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128 changes: 128 additions & 0 deletions tests/baselines/reference/returnTypeTopLevelInferenceLiteralDontWiden1.symbols
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//// [tests/cases/compiler/returnTypeTopLevelInferenceLiteralDontWiden1.ts] ////

=== returnTypeTopLevelInferenceLiteralDontWiden1.ts ===
declare function A<T>(value: T): T extends string ? T : never;
>A : Symbol(A, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 0, 0))
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 0, 19))
>value : Symbol(value, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 0, 22))
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 0, 19))
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 0, 19))
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 0, 19))

const ATest = A("foo");
>ATest : Symbol(ATest, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 2, 5))
>A : Symbol(A, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 0, 0))

declare function B<T>(value: T): `test_${T & string}`;
>B : Symbol(B, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 2, 23))
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 4, 19))
>value : Symbol(value, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 4, 22))
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 4, 19))
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 4, 19))

const BTest = B("foo");
>BTest : Symbol(BTest, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 6, 5))
>B : Symbol(B, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 2, 23))

declare function C<T>(
>C : Symbol(C, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 6, 23))
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 8, 19))

value: T,
>value : Symbol(value, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 8, 22))
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 8, 19))

): T extends string
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 8, 19))

? T
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 8, 19))

: T extends number | bigint | boolean | null | undefined
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 8, 19))

? `test_${T}`
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 8, 19))

: never;

const CTest = C("foo");
>CTest : Symbol(CTest, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 16, 5))
>C : Symbol(C, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 6, 23))

declare function D<T>(value: T): T extends number ? `test_${T}` : T;
>D : Symbol(D, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 16, 23))
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 18, 19))
>value : Symbol(value, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 18, 22))
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 18, 19))
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 18, 19))
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 18, 19))
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 18, 19))

const DTest = D("foo");
>DTest : Symbol(DTest, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 20, 5))
>D : Symbol(D, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 16, 23))

declare function E<T>(value: T): T extends string ? `test_${T}` : T;
>E : Symbol(E, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 20, 23))
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 22, 19))
>value : Symbol(value, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 22, 22))
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 22, 19))
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 22, 19))
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 22, 19))
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 22, 19))

const ETest = E("foo");
>ETest : Symbol(ETest, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 24, 5))
>E : Symbol(E, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 20, 23))

declare function F<T>(value: T): T extends number ? `test_${T}` : [T];
>F : Symbol(F, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 24, 23))
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 26, 19))
>value : Symbol(value, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 26, 22))
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 26, 19))
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 26, 19))
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 26, 19))
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 26, 19))

const FTest1 = F("foo");
>FTest1 : Symbol(FTest1, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 28, 5))
>F : Symbol(F, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 24, 23))

const FTest2 = F(42);
>FTest2 : Symbol(FTest2, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 29, 5))
>F : Symbol(F, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 24, 23))

declare function G<T>(value: T): T extends string ? `test_${T}` : [T];
>G : Symbol(G, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 29, 21))
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 31, 19))
>value : Symbol(value, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 31, 22))
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 31, 19))
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 31, 19))
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 31, 19))
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 31, 19))

const GTest1 = G("foo");
>GTest1 : Symbol(GTest1, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 33, 5))
>G : Symbol(G, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 29, 21))

const GTest2 = G(42);
>GTest2 : Symbol(GTest2, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 34, 5))
>G : Symbol(G, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 29, 21))

declare function H<T>(
>H : Symbol(H, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 34, 21))
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 36, 19))

value: T,
>value : Symbol(value, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 36, 22))
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 36, 19))

): T extends number ? never : `test_${T & string}`;
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 36, 19))
>T : Symbol(T, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 36, 19))

const HTest = H("foo");
>HTest : Symbol(HTest, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 40, 5))
>H : Symbol(H, Decl(returnTypeTopLevelInferenceLiteralDontWiden1.ts, 34, 21))

163 changes: 163 additions & 0 deletions tests/baselines/reference/returnTypeTopLevelInferenceLiteralDontWiden1.types
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//// [tests/cases/compiler/returnTypeTopLevelInferenceLiteralDontWiden1.ts] ////

=== returnTypeTopLevelInferenceLiteralDontWiden1.ts ===
declare function A<T>(value: T): T extends string ? T : never;
>A : <T>(value: T) => T extends string ? T : never
> : ^ ^^ ^^ ^^^^^
>value : T
> : ^

const ATest = A("foo");
>ATest : "foo"
> : ^^^^^
>A("foo") : "foo"
> : ^^^^^
>A : <T>(value: T) => T extends string ? T : never
> : ^ ^^ ^^ ^^^^^
>"foo" : "foo"
> : ^^^^^

declare function B<T>(value: T): `test_${T & string}`;
>B : <T>(value: T) => `test_${T & string}`
> : ^ ^^ ^^ ^^^^^
>value : T
> : ^

const BTest = B("foo");
>BTest : "test_foo"
> : ^^^^^^^^^^
>B("foo") : "test_foo"
> : ^^^^^^^^^^
>B : <T>(value: T) => `test_${T & string}`
> : ^ ^^ ^^ ^^^^^
>"foo" : "foo"
> : ^^^^^

declare function C<T>(
>C : <T>(value: T) => T extends string ? T : T extends number | bigint | boolean | null | undefined ? `test_${T}` : never
> : ^ ^^ ^^ ^^^^^

value: T,
>value : T
> : ^

): T extends string
? T
: T extends number | bigint | boolean | null | undefined
? `test_${T}`
: never;

const CTest = C("foo");
>CTest : "foo"
> : ^^^^^
>C("foo") : "foo"
> : ^^^^^
>C : <T>(value: T) => T extends string ? T : T extends number | bigint | boolean | null | undefined ? `test_${T}` : never
> : ^ ^^ ^^ ^^^^^
>"foo" : "foo"
> : ^^^^^

declare function D<T>(value: T): T extends number ? `test_${T}` : T;
>D : <T>(value: T) => T extends number ? `test_${T}` : T
> : ^ ^^ ^^ ^^^^^
>value : T
> : ^

const DTest = D("foo");
>DTest : "foo"
> : ^^^^^
>D("foo") : "foo"
> : ^^^^^
>D : <T>(value: T) => T extends number ? `test_${T}` : T
> : ^ ^^ ^^ ^^^^^
>"foo" : "foo"
> : ^^^^^

declare function E<T>(value: T): T extends string ? `test_${T}` : T;
>E : <T>(value: T) => T extends string ? `test_${T}` : T
> : ^ ^^ ^^ ^^^^^
>value : T
> : ^

const ETest = E("foo");
>ETest : "test_foo"
> : ^^^^^^^^^^
>E("foo") : "test_foo"
> : ^^^^^^^^^^
>E : <T>(value: T) => T extends string ? `test_${T}` : T
> : ^ ^^ ^^ ^^^^^
>"foo" : "foo"
> : ^^^^^

declare function F<T>(value: T): T extends number ? `test_${T}` : [T];
>F : <T>(value: T) => T extends number ? `test_${T}` : [T]
> : ^ ^^ ^^ ^^^^^
>value : T
> : ^

const FTest1 = F("foo");
>FTest1 : ["foo"]
> : ^^^^^^^
>F("foo") : ["foo"]
> : ^^^^^^^
>F : <T>(value: T) => T extends number ? `test_${T}` : [T]
> : ^ ^^ ^^ ^^^^^
>"foo" : "foo"
> : ^^^^^

const FTest2 = F(42);
>FTest2 : "test_42"
> : ^^^^^^^^^
>F(42) : "test_42"
> : ^^^^^^^^^
>F : <T>(value: T) => T extends number ? `test_${T}` : [T]
> : ^ ^^ ^^ ^^^^^
>42 : 42
> : ^^

declare function G<T>(value: T): T extends string ? `test_${T}` : [T];
>G : <T>(value: T) => T extends string ? `test_${T}` : [T]
> : ^ ^^ ^^ ^^^^^
>value : T
> : ^

const GTest1 = G("foo");
>GTest1 : "test_foo"
> : ^^^^^^^^^^
>G("foo") : "test_foo"
> : ^^^^^^^^^^
>G : <T>(value: T) => T extends string ? `test_${T}` : [T]
> : ^ ^^ ^^ ^^^^^
>"foo" : "foo"
> : ^^^^^

const GTest2 = G(42);
>GTest2 : [42]
> : ^^^^
>G(42) : [42]
> : ^^^^
>G : <T>(value: T) => T extends string ? `test_${T}` : [T]
> : ^ ^^ ^^ ^^^^^
>42 : 42
> : ^^

declare function H<T>(
>H : <T>(value: T) => T extends number ? never : `test_${T & string}`
> : ^ ^^ ^^ ^^^^^

value: T,
>value : T
> : ^

): T extends number ? never : `test_${T & string}`;

const HTest = H("foo");
>HTest : "test_foo"
> : ^^^^^^^^^^
>H("foo") : "test_foo"
> : ^^^^^^^^^^
>H : <T>(value: T) => T extends number ? never : `test_${T & string}`
> : ^ ^^ ^^ ^^^^^
>"foo" : "foo"
> : ^^^^^

44 changes: 44 additions & 0 deletions tests/cases/compiler/returnTypeTopLevelInferenceLiteralDontWiden1.ts
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// @strict: true
// @noEmit: true

declare function A<T>(value: T): T extends string ? T : never;

const ATest = A("foo");

declare function B<T>(value: T): `test_${T & string}`;

const BTest = B("foo");

declare function C<T>(
value: T,
): T extends string
? T
: T extends number | bigint | boolean | null | undefined
? `test_${T}`
: never;

const CTest = C("foo");

declare function D<T>(value: T): T extends number ? `test_${T}` : T;

const DTest = D("foo");

declare function E<T>(value: T): T extends string ? `test_${T}` : T;

const ETest = E("foo");

declare function F<T>(value: T): T extends number ? `test_${T}` : [T];

const FTest1 = F("foo");
const FTest2 = F(42);

declare function G<T>(value: T): T extends string ? `test_${T}` : [T];

const GTest1 = G("foo");
const GTest2 = G(42);

declare function H<T>(
value: T,
): T extends number ? never : `test_${T & string}`;

const HTest = H("foo");
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