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Improve inference for a tuple target with 2 middle variadic elements and implied arity for the latter #56976

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29cdfb8
Improve inference for a tuple target with 2 middle variadic elements …
Andarist Jan 8, 2024
ecd3b57
Fixed a case with extra trailing end element
Andarist Jan 8, 2024
a842c5e
Merge remote-tracking branch 'origin/main' into improve-inference-2-v…
Andarist Oct 8, 2025
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7 changes: 6 additions & 1 deletion src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -27316,12 +27316,17 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
if (middleLength === 2) {
if (elementFlags[startLength] & elementFlags[startLength + 1] & ElementFlags.Variadic) {
// Middle of target is [...T, ...U] and source is tuple type
const targetInfo = getInferenceInfoForType(elementTypes[startLength]);
let targetInfo = getInferenceInfoForType(elementTypes[startLength]);
if (targetInfo && targetInfo.impliedArity !== undefined) {
// Infer slices from source based on implied arity of T.
inferFromTypes(sliceTupleType(source, startLength, endLength + sourceArity - targetInfo.impliedArity), elementTypes[startLength]);
inferFromTypes(sliceTupleType(source, startLength + targetInfo.impliedArity, endLength), elementTypes[startLength + 1]);
}
else if ((targetInfo = getInferenceInfoForType(elementTypes[startLength + 1]))?.impliedArity !== undefined) {
// Infer slices from source based on implied arity of U.
inferFromTypes(sliceTupleType(source, startLength, endLength + targetInfo!.impliedArity), elementTypes[startLength]);
inferFromTypes(sliceTupleType(source, startLength + sourceArity - endLength - targetInfo!.impliedArity, endLength), elementTypes[startLength + 1]);
}
}
else if (elementFlags[startLength] & ElementFlags.Variadic && elementFlags[startLength + 1] & ElementFlags.Rest) {
// Middle of target is [...T, ...rest] and source is tuple type
Expand Down
140 changes: 140 additions & 0 deletions tests/baselines/reference/variadicTuples4.symbols
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@@ -0,0 +1,140 @@
//// [tests/cases/conformance/types/tuple/variadicTuples4.ts] ////

=== variadicTuples4.ts ===
// https://github.com/microsoft/TypeScript/issues/56970

function partialCall1<T extends readonly any[], U extends readonly any[], R>(
>partialCall1 : Symbol(partialCall1, Decl(variadicTuples4.ts, 0, 0))
>T : Symbol(T, Decl(variadicTuples4.ts, 2, 22))
>U : Symbol(U, Decl(variadicTuples4.ts, 2, 47))
>R : Symbol(R, Decl(variadicTuples4.ts, 2, 73))

f: (...args: [...U, ...T]) => R,
>f : Symbol(f, Decl(variadicTuples4.ts, 2, 77))
>args : Symbol(args, Decl(variadicTuples4.ts, 3, 6))
>U : Symbol(U, Decl(variadicTuples4.ts, 2, 47))
>T : Symbol(T, Decl(variadicTuples4.ts, 2, 22))
>R : Symbol(R, Decl(variadicTuples4.ts, 2, 73))

...tailArgs: T
>tailArgs : Symbol(tailArgs, Decl(variadicTuples4.ts, 3, 34))
>T : Symbol(T, Decl(variadicTuples4.ts, 2, 22))

) {
return (...headArgs: U) => f(...headArgs, ...tailArgs);
>headArgs : Symbol(headArgs, Decl(variadicTuples4.ts, 6, 10))
>U : Symbol(U, Decl(variadicTuples4.ts, 2, 47))
>f : Symbol(f, Decl(variadicTuples4.ts, 2, 77))
>headArgs : Symbol(headArgs, Decl(variadicTuples4.ts, 6, 10))
>tailArgs : Symbol(tailArgs, Decl(variadicTuples4.ts, 3, 34))
}

function source1(a: number, b: number, c: number): number {
>source1 : Symbol(source1, Decl(variadicTuples4.ts, 7, 1))
>a : Symbol(a, Decl(variadicTuples4.ts, 9, 17))
>b : Symbol(b, Decl(variadicTuples4.ts, 9, 27))
>c : Symbol(c, Decl(variadicTuples4.ts, 9, 38))

return a + b + c;
>a : Symbol(a, Decl(variadicTuples4.ts, 9, 17))
>b : Symbol(b, Decl(variadicTuples4.ts, 9, 27))
>c : Symbol(c, Decl(variadicTuples4.ts, 9, 38))
}

const result1 = partialCall1(source1, 1);
>result1 : Symbol(result1, Decl(variadicTuples4.ts, 13, 5))
>partialCall1 : Symbol(partialCall1, Decl(variadicTuples4.ts, 0, 0))
>source1 : Symbol(source1, Decl(variadicTuples4.ts, 7, 1))

function partialCall2<T extends readonly any[], U extends readonly any[], R>(
>partialCall2 : Symbol(partialCall2, Decl(variadicTuples4.ts, 13, 41))
>T : Symbol(T, Decl(variadicTuples4.ts, 15, 22))
>U : Symbol(U, Decl(variadicTuples4.ts, 15, 47))
>R : Symbol(R, Decl(variadicTuples4.ts, 15, 73))

f: (...args: [number, ...U, ...T]) => R,
>f : Symbol(f, Decl(variadicTuples4.ts, 15, 77))
>args : Symbol(args, Decl(variadicTuples4.ts, 16, 6))
>U : Symbol(U, Decl(variadicTuples4.ts, 15, 47))
>T : Symbol(T, Decl(variadicTuples4.ts, 15, 22))
>R : Symbol(R, Decl(variadicTuples4.ts, 15, 73))

...tailArgs: T
>tailArgs : Symbol(tailArgs, Decl(variadicTuples4.ts, 16, 42))
>T : Symbol(T, Decl(variadicTuples4.ts, 15, 22))

) {
return (...headArgs: U) => f(0, ...headArgs, ...tailArgs);
>headArgs : Symbol(headArgs, Decl(variadicTuples4.ts, 19, 10))
>U : Symbol(U, Decl(variadicTuples4.ts, 15, 47))
>f : Symbol(f, Decl(variadicTuples4.ts, 15, 77))
>headArgs : Symbol(headArgs, Decl(variadicTuples4.ts, 19, 10))
>tailArgs : Symbol(tailArgs, Decl(variadicTuples4.ts, 16, 42))
}

function source2(a: number, b: number, c: number, d: number): number {
>source2 : Symbol(source2, Decl(variadicTuples4.ts, 20, 1))
>a : Symbol(a, Decl(variadicTuples4.ts, 22, 17))
>b : Symbol(b, Decl(variadicTuples4.ts, 22, 27))
>c : Symbol(c, Decl(variadicTuples4.ts, 22, 38))
>d : Symbol(d, Decl(variadicTuples4.ts, 22, 49))

return a + b + c + d;
>a : Symbol(a, Decl(variadicTuples4.ts, 22, 17))
>b : Symbol(b, Decl(variadicTuples4.ts, 22, 27))
>c : Symbol(c, Decl(variadicTuples4.ts, 22, 38))
>d : Symbol(d, Decl(variadicTuples4.ts, 22, 49))
}

const result2 = partialCall2(source2, 1);
>result2 : Symbol(result2, Decl(variadicTuples4.ts, 26, 5))
>partialCall2 : Symbol(partialCall2, Decl(variadicTuples4.ts, 13, 41))
>source2 : Symbol(source2, Decl(variadicTuples4.ts, 20, 1))

function partialCall3<T extends readonly any[], U extends readonly any[], R>(
>partialCall3 : Symbol(partialCall3, Decl(variadicTuples4.ts, 26, 41))
>T : Symbol(T, Decl(variadicTuples4.ts, 28, 22))
>U : Symbol(U, Decl(variadicTuples4.ts, 28, 47))
>R : Symbol(R, Decl(variadicTuples4.ts, 28, 73))

f: (...args: [...U, ...T, number]) => R,
>f : Symbol(f, Decl(variadicTuples4.ts, 28, 77))
>args : Symbol(args, Decl(variadicTuples4.ts, 29, 6))
>U : Symbol(U, Decl(variadicTuples4.ts, 28, 47))
>T : Symbol(T, Decl(variadicTuples4.ts, 28, 22))
>R : Symbol(R, Decl(variadicTuples4.ts, 28, 73))

...tailArgs: T
>tailArgs : Symbol(tailArgs, Decl(variadicTuples4.ts, 29, 42))
>T : Symbol(T, Decl(variadicTuples4.ts, 28, 22))

) {
return (...headArgs: U) => f(...headArgs, ...tailArgs, 100);
>headArgs : Symbol(headArgs, Decl(variadicTuples4.ts, 32, 10))
>U : Symbol(U, Decl(variadicTuples4.ts, 28, 47))
>f : Symbol(f, Decl(variadicTuples4.ts, 28, 77))
>headArgs : Symbol(headArgs, Decl(variadicTuples4.ts, 32, 10))
>tailArgs : Symbol(tailArgs, Decl(variadicTuples4.ts, 29, 42))
}

function source3(a: number, b: number, c: number, d: number): number {
>source3 : Symbol(source3, Decl(variadicTuples4.ts, 33, 1))
>a : Symbol(a, Decl(variadicTuples4.ts, 35, 17))
>b : Symbol(b, Decl(variadicTuples4.ts, 35, 27))
>c : Symbol(c, Decl(variadicTuples4.ts, 35, 38))
>d : Symbol(d, Decl(variadicTuples4.ts, 35, 49))

return a + b + c + d;
>a : Symbol(a, Decl(variadicTuples4.ts, 35, 17))
>b : Symbol(b, Decl(variadicTuples4.ts, 35, 27))
>c : Symbol(c, Decl(variadicTuples4.ts, 35, 38))
>d : Symbol(d, Decl(variadicTuples4.ts, 35, 49))
}

const result3 = partialCall3(source3, 1);
>result3 : Symbol(result3, Decl(variadicTuples4.ts, 39, 5))
>partialCall3 : Symbol(partialCall3, Decl(variadicTuples4.ts, 26, 41))
>source3 : Symbol(source3, Decl(variadicTuples4.ts, 33, 1))

export {}

224 changes: 224 additions & 0 deletions tests/baselines/reference/variadicTuples4.types
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Original file line number Diff line number Diff line change
@@ -0,0 +1,224 @@
//// [tests/cases/conformance/types/tuple/variadicTuples4.ts] ////

=== variadicTuples4.ts ===
// https://github.com/microsoft/TypeScript/issues/56970

function partialCall1<T extends readonly any[], U extends readonly any[], R>(
>partialCall1 : <T extends readonly any[], U extends readonly any[], R>(f: (...args: [...U, ...T]) => R, ...tailArgs: T) => (...headArgs: U) => R
> : ^ ^^^^^^^^^ ^^ ^^^^^^^^^ ^^ ^^ ^^ ^^^^^ ^^ ^^^^^^ ^^^^^^

f: (...args: [...U, ...T]) => R,
>f : (...args: [...U, ...T]) => R
> : ^^^^ ^^ ^^^^^
>args : [...U, ...T]
> : ^^^^^^^^^^^^

...tailArgs: T
>tailArgs : T
> : ^

) {
return (...headArgs: U) => f(...headArgs, ...tailArgs);
>(...headArgs: U) => f(...headArgs, ...tailArgs) : (...headArgs: U) => R
> : ^^^^ ^^ ^^^^^^
>headArgs : U
> : ^
>f(...headArgs, ...tailArgs) : R
> : ^
>f : (...args: [...U, ...T]) => R
> : ^^^^ ^^ ^^^^^
>...headArgs : any
>headArgs : U
> : ^
>...tailArgs : any
>tailArgs : T
> : ^
}

function source1(a: number, b: number, c: number): number {
>source1 : (a: number, b: number, c: number) => number
> : ^ ^^ ^^ ^^ ^^ ^^ ^^^^^
>a : number
> : ^^^^^^
>b : number
> : ^^^^^^
>c : number
> : ^^^^^^

return a + b + c;
>a + b + c : number
> : ^^^^^^
>a + b : number
> : ^^^^^^
>a : number
> : ^^^^^^
>b : number
> : ^^^^^^
>c : number
> : ^^^^^^
}

const result1 = partialCall1(source1, 1);
>result1 : (a: number, b: number) => number
> : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>partialCall1(source1, 1) : (a: number, b: number) => number
> : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>partialCall1 : <T extends readonly any[], U extends readonly any[], R>(f: (...args: [...U, ...T]) => R, ...tailArgs: T) => (...headArgs: U) => R
> : ^ ^^^^^^^^^ ^^ ^^^^^^^^^ ^^ ^^ ^^ ^^^^^ ^^ ^^^^^^ ^^^^^^
>source1 : (a: number, b: number, c: number) => number
> : ^ ^^ ^^ ^^ ^^ ^^ ^^^^^
>1 : 1
> : ^

function partialCall2<T extends readonly any[], U extends readonly any[], R>(
>partialCall2 : <T extends readonly any[], U extends readonly any[], R>(f: (...args: [number, ...U, ...T]) => R, ...tailArgs: T) => (...headArgs: U) => R
> : ^ ^^^^^^^^^ ^^ ^^^^^^^^^ ^^ ^^ ^^ ^^^^^ ^^ ^^^^^^ ^^^^^^

f: (...args: [number, ...U, ...T]) => R,
>f : (...args: [number, ...U, ...T]) => R
> : ^^^^ ^^ ^^^^^
>args : [number, ...U, ...T]
> : ^^^^^^^^^^^^^^^^^^^^

...tailArgs: T
>tailArgs : T
> : ^

) {
return (...headArgs: U) => f(0, ...headArgs, ...tailArgs);
>(...headArgs: U) => f(0, ...headArgs, ...tailArgs) : (...headArgs: U) => R
> : ^^^^ ^^ ^^^^^^
>headArgs : U
> : ^
>f(0, ...headArgs, ...tailArgs) : R
> : ^
>f : (...args: [number, ...U, ...T]) => R
> : ^^^^ ^^ ^^^^^
>0 : 0
> : ^
>...headArgs : any
>headArgs : U
> : ^
>...tailArgs : any
>tailArgs : T
> : ^
}

function source2(a: number, b: number, c: number, d: number): number {
>source2 : (a: number, b: number, c: number, d: number) => number
> : ^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^^^^
>a : number
> : ^^^^^^
>b : number
> : ^^^^^^
>c : number
> : ^^^^^^
>d : number
> : ^^^^^^

return a + b + c + d;
>a + b + c + d : number
> : ^^^^^^
>a + b + c : number
> : ^^^^^^
>a + b : number
> : ^^^^^^
>a : number
> : ^^^^^^
>b : number
> : ^^^^^^
>c : number
> : ^^^^^^
>d : number
> : ^^^^^^
}

const result2 = partialCall2(source2, 1);
>result2 : (b: number, c: number) => number
> : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>partialCall2(source2, 1) : (b: number, c: number) => number
> : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>partialCall2 : <T extends readonly any[], U extends readonly any[], R>(f: (...args: [number, ...U, ...T]) => R, ...tailArgs: T) => (...headArgs: U) => R
> : ^ ^^^^^^^^^ ^^ ^^^^^^^^^ ^^ ^^ ^^ ^^^^^ ^^ ^^^^^^ ^^^^^^
>source2 : (a: number, b: number, c: number, d: number) => number
> : ^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^^^^
>1 : 1
> : ^

function partialCall3<T extends readonly any[], U extends readonly any[], R>(
>partialCall3 : <T extends readonly any[], U extends readonly any[], R>(f: (...args: [...U, ...T, number]) => R, ...tailArgs: T) => (...headArgs: U) => R
> : ^ ^^^^^^^^^ ^^ ^^^^^^^^^ ^^ ^^ ^^ ^^^^^ ^^ ^^^^^^ ^^^^^^

f: (...args: [...U, ...T, number]) => R,
>f : (...args: [...U, ...T, number]) => R
> : ^^^^ ^^ ^^^^^
>args : [...U, ...T, number]
> : ^^^^^^^^^^^^^^^^^^^^

...tailArgs: T
>tailArgs : T
> : ^

) {
return (...headArgs: U) => f(...headArgs, ...tailArgs, 100);
>(...headArgs: U) => f(...headArgs, ...tailArgs, 100) : (...headArgs: U) => R
> : ^^^^ ^^ ^^^^^^
>headArgs : U
> : ^
>f(...headArgs, ...tailArgs, 100) : R
> : ^
>f : (...args: [...U, ...T, number]) => R
> : ^^^^ ^^ ^^^^^
>...headArgs : any
>headArgs : U
> : ^
>...tailArgs : any
>tailArgs : T
> : ^
>100 : 100
> : ^^^
}

function source3(a: number, b: number, c: number, d: number): number {
>source3 : (a: number, b: number, c: number, d: number) => number
> : ^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^^^^
>a : number
> : ^^^^^^
>b : number
> : ^^^^^^
>c : number
> : ^^^^^^
>d : number
> : ^^^^^^

return a + b + c + d;
>a + b + c + d : number
> : ^^^^^^
>a + b + c : number
> : ^^^^^^
>a + b : number
> : ^^^^^^
>a : number
> : ^^^^^^
>b : number
> : ^^^^^^
>c : number
> : ^^^^^^
>d : number
> : ^^^^^^
}

const result3 = partialCall3(source3, 1);
>result3 : (a: number, b: number) => number
> : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>partialCall3(source3, 1) : (a: number, b: number) => number
> : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>partialCall3 : <T extends readonly any[], U extends readonly any[], R>(f: (...args: [...U, ...T, number]) => R, ...tailArgs: T) => (...headArgs: U) => R
> : ^ ^^^^^^^^^ ^^ ^^^^^^^^^ ^^ ^^ ^^ ^^^^^ ^^ ^^^^^^ ^^^^^^
>source3 : (a: number, b: number, c: number, d: number) => number
> : ^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^^^^
>1 : 1
> : ^

export {}

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