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Merged
merged 3 commits into from
Jun 10, 2025
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Make anyFunctionType a subtype of all function types #1149

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aa69996
Make anyFunctionType a subtype of all function types
ahejlsberg Jun 10, 2025
1928d84
Accept new baselines
ahejlsberg Jun 10, 2025
ba2b3f4
Add regression test
ahejlsberg Jun 10, 2025
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6 changes: 5 additions & 1 deletion internal/checker/relater.go
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Original file line number Diff line number Diff line change
Expand Up @@ -4359,9 +4359,13 @@ func (r *Relater) signaturesRelatedTo(source *Type, target *Type, kind Signature
if r.relation == r.c.identityRelation {
return r.signaturesIdenticalTo(source, target, kind)
}
if target == r.c.anyFunctionType || r.relation != r.c.strictSubtypeRelation && source == r.c.anyFunctionType {
// With respect to signatures, the anyFunctionType wildcard is a subtype of every other function type.
if source == r.c.anyFunctionType {
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Copilot AI Jun 10, 2025

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The unconditional TernaryTrue when source is anyFunctionType bypasses signature checks (including return types), which could incorrectly mark incompatible function signatures as subtypes. Consider preserving return-type compatibility or narrowing the early return condition.

Suggested change
if source == r.c.anyFunctionType {
if source == r.c.anyFunctionType {
sourceSignatures := r.c.getSignaturesOfType(source, kind)
targetSignatures := r.c.getSignaturesOfType(target, kind)
for _, s := range sourceSignatures {
for _, t := range targetSignatures {
if r.signatureRelatedTo(s, t, true /*erase*/, reportErrors, intersectionState) == TernaryFalse {
return TernaryFalse
}
}
}

Copilot uses AI. Check for mistakes.

return TernaryTrue
}
if target == r.c.anyFunctionType {
return TernaryFalse
}
sourceSignatures := r.c.getSignaturesOfType(source, kind)
targetSignatures := r.c.getSignaturesOfType(target, kind)
if kind == SignatureKindConstruct && len(sourceSignatures) != 0 && len(targetSignatures) != 0 {
Expand Down
31 changes: 31 additions & 0 deletions testdata/baselines/reference/compiler/subtypeReductionWithAnyFunctionType.errors.txt
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@@ -0,0 +1,31 @@
subtypeReductionWithAnyFunctionType.ts(10,16): error TS7006: Parameter 'x' implicitly has an 'any' type.


==== subtypeReductionWithAnyFunctionType.ts (1 errors) ====
// https://github.com/microsoft/typescript-go/issues/849

declare function useMemo<T>(func: () => T): T;

function getPredicate(alwaysTrue: boolean) {
const predicate: (input: string) => boolean = useMemo(() => {
if (alwaysTrue) {
return () => true;
}
return x => x.length > 0;
~
!!! error TS7006: Parameter 'x' implicitly has an 'any' type.
});
return predicate;
}

// https://github.com/microsoft/typescript-go/issues/1016

declare function compact<T>(array: T[]): T[];
declare function makeFooer(): Fooer;
interface Fooer {
foo: (v: string) => string;
}
function f() {
const _ = compact([makeFooer(), { foo: (v) => v }]);
}

34 changes: 32 additions & 2 deletions testdata/baselines/reference/compiler/subtypeReductionWithAnyFunctionType.symbols
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Expand Up @@ -26,12 +26,42 @@ function getPredicate(alwaysTrue: boolean) {
}
return x => x.length > 0;
>x : Symbol(x, Decl(subtypeReductionWithAnyFunctionType.ts, 9, 14))
>x.length : Symbol(length, Decl(lib.es5.d.ts, --, --))
>x : Symbol(x, Decl(subtypeReductionWithAnyFunctionType.ts, 9, 14))
>length : Symbol(length, Decl(lib.es5.d.ts, --, --))

});
return predicate;
>predicate : Symbol(predicate, Decl(subtypeReductionWithAnyFunctionType.ts, 5, 9))
}

// https://github.com/microsoft/typescript-go/issues/1016

declare function compact<T>(array: T[]): T[];
>compact : Symbol(compact, Decl(subtypeReductionWithAnyFunctionType.ts, 12, 1))
>T : Symbol(T, Decl(subtypeReductionWithAnyFunctionType.ts, 16, 25))
>array : Symbol(array, Decl(subtypeReductionWithAnyFunctionType.ts, 16, 28))
>T : Symbol(T, Decl(subtypeReductionWithAnyFunctionType.ts, 16, 25))
>T : Symbol(T, Decl(subtypeReductionWithAnyFunctionType.ts, 16, 25))

declare function makeFooer(): Fooer;
>makeFooer : Symbol(makeFooer, Decl(subtypeReductionWithAnyFunctionType.ts, 16, 45))
>Fooer : Symbol(Fooer, Decl(subtypeReductionWithAnyFunctionType.ts, 17, 36))

interface Fooer {
>Fooer : Symbol(Fooer, Decl(subtypeReductionWithAnyFunctionType.ts, 17, 36))

foo: (v: string) => string;
>foo : Symbol(foo, Decl(subtypeReductionWithAnyFunctionType.ts, 18, 17))
>v : Symbol(v, Decl(subtypeReductionWithAnyFunctionType.ts, 19, 10))
}
function f() {
>f : Symbol(f, Decl(subtypeReductionWithAnyFunctionType.ts, 20, 1))

const _ = compact([makeFooer(), { foo: (v) => v }]);
>_ : Symbol(_, Decl(subtypeReductionWithAnyFunctionType.ts, 22, 9))
>compact : Symbol(compact, Decl(subtypeReductionWithAnyFunctionType.ts, 12, 1))
>makeFooer : Symbol(makeFooer, Decl(subtypeReductionWithAnyFunctionType.ts, 16, 45))
>foo : Symbol(foo, Decl(subtypeReductionWithAnyFunctionType.ts, 22, 37))
>v : Symbol(v, Decl(subtypeReductionWithAnyFunctionType.ts, 22, 44))
>v : Symbol(v, Decl(subtypeReductionWithAnyFunctionType.ts, 22, 44))
}

45 changes: 38 additions & 7 deletions testdata/baselines/reference/compiler/subtypeReductionWithAnyFunctionType.types
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Original file line number Diff line number Diff line change
Expand Up @@ -14,9 +14,9 @@ function getPredicate(alwaysTrue: boolean) {
const predicate: (input: string) => boolean = useMemo(() => {
>predicate : (input: string) => boolean
>input : string
>useMemo(() => { if (alwaysTrue) { return () => true; } return x => x.length > 0; }) : (x: string) => boolean
>useMemo(() => { if (alwaysTrue) { return () => true; } return x => x.length > 0; }) : (x: any) => boolean
>useMemo : <T>(func: () => T) => T
>() => { if (alwaysTrue) { return () => true; } return x => x.length > 0; } : () => (x: string) => boolean
>() => { if (alwaysTrue) { return () => true; } return x => x.length > 0; } : () => (x: any) => boolean

if (alwaysTrue) {
>alwaysTrue : boolean
Expand All @@ -26,16 +26,47 @@ function getPredicate(alwaysTrue: boolean) {
>true : true
}
return x => x.length > 0;
>x => x.length > 0 : (x: string) => boolean
>x : string
>x => x.length > 0 : (x: any) => boolean
>x : any
>x.length > 0 : boolean
>x.length : number
>x : string
>length : number
>x.length : any
>x : any
>length : any
>0 : 0

});
return predicate;
>predicate : (input: string) => boolean
}

// https://github.com/microsoft/typescript-go/issues/1016

declare function compact<T>(array: T[]): T[];
>compact : <T>(array: T[]) => T[]
>array : T[]

declare function makeFooer(): Fooer;
>makeFooer : () => Fooer

interface Fooer {
foo: (v: string) => string;
>foo : (v: string) => string
>v : string
}
function f() {
>f : () => void

const _ = compact([makeFooer(), { foo: (v) => v }]);
>_ : Fooer[]
>compact([makeFooer(), { foo: (v) => v }]) : Fooer[]
>compact : <T>(array: T[]) => T[]
>[makeFooer(), { foo: (v) => v }] : Fooer[]
>makeFooer() : Fooer
>makeFooer : () => Fooer
>{ foo: (v) => v } : { foo: (v: string) => string; }
>foo : (v: string) => string
>(v) => v : (v: string) => string
>v : string
>v : string
}

11 changes: 11 additions & 0 deletions testdata/tests/cases/compiler/subtypeReductionWithAnyFunctionType.ts
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Expand Up @@ -15,3 +15,14 @@ function getPredicate(alwaysTrue: boolean) {
});
return predicate;
}

// https://github.com/microsoft/typescript-go/issues/1016

declare function compact<T>(array: T[]): T[];
declare function makeFooer(): Fooer;
interface Fooer {
foo: (v: string) => string;
}
function f() {
const _ = compact([makeFooer(), { foo: (v) => v }]);
}