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Mateusz Burzyński (Andarist) wants to merge 6 commits into from
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Reuse single errored signature candidate as resolved signature #61787

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a1521b0
Reuse single errored signature candidate as resolved signature
Andarist May 30, 2025
2f62ee0
push the fix to `pickLongestCandidateSignature` so the out candidates…
Andarist May 31, 2025
99201b2
don't be afraid of overloads
Andarist Jun 6, 2025
808220c
Merge remote-tracking branch 'origin/main' into reuse-errored-signatures
Andarist Nov 21, 2025
3c159d0
Merge remote-tracking branch 'origin/main' into reuse-errored-signatures
Andarist Dec 5, 2025
bf02bd3
make one of the tests a module
Andarist Dec 10, 2025
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12 changes: 9 additions & 3 deletions src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -36385,7 +36385,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
if (result) {
return result;
}
result = getCandidateForOverloadFailure(node, candidates, args, !!candidatesOutArray, checkMode);
result = getCandidateForOverloadFailure(node, candidates, candidatesForArgumentError, args, !!candidatesOutArray, checkMode);
// Preemptively cache the result; getResolvedSignature will do this after we return, but
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// we need to ensure that the result is present for the error checks below so that if
// this signature is encountered again, we handle the circularity (rather than producing a
Expand Down Expand Up @@ -36616,6 +36616,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
function getCandidateForOverloadFailure(
node: CallLikeExpression,
candidates: Signature[],
candidatesForArgumentError: Signature[] | undefined,
args: readonly Expression[],
hasCandidatesOutArray: boolean,
checkMode: CheckMode,
Expand All @@ -36626,7 +36627,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
// Don't do this if there is a `candidatesOutArray`,
// because then we want the chosen best candidate to be one of the overloads, not a combination.
return hasCandidatesOutArray || candidates.length === 1 || candidates.some(c => !!c.typeParameters)
? pickLongestCandidateSignature(node, candidates, args, checkMode)
? pickLongestCandidateSignature(node, candidates, candidatesForArgumentError, args, checkMode)
: createUnionOfSignaturesForOverloadFailure(candidates);
}

Expand Down Expand Up @@ -36682,7 +36683,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
return createSymbolWithType(first(sources), type);
}

function pickLongestCandidateSignature(node: CallLikeExpression, candidates: Signature[], args: readonly Expression[], checkMode: CheckMode): Signature {
function pickLongestCandidateSignature(node: CallLikeExpression, candidates: Signature[], candidatesForArgumentError: Signature[] | undefined, args: readonly Expression[], checkMode: CheckMode): Signature {
// Pick the longest signature. This way we can get a contextual type for cases like:
// declare function f(a: { xa: number; xb: number; }, b: number);
// f({ |
Expand All @@ -36699,6 +36700,11 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
const typeArgumentNodes: readonly TypeNode[] | undefined = callLikeExpressionMayHaveTypeArguments(node) ? node.typeArguments : undefined;
const instantiated = typeArgumentNodes
? createSignatureInstantiation(candidate, getTypeArgumentsFromNodes(typeArgumentNodes, typeParameters, isInJSFile(node)))
// when there is only one candidate reuse existing *inferred* candidate for argument error (if available)
// this saves the compiler some extra work but more importantly it includes inferences made from context-sensitive arguments and generic functions
// which avoids confusing mismatches between inferred type arguments and reported argument error
: candidates.length === 1 && candidatesForArgumentError
? candidatesForArgumentError[0]
: inferSignatureInstantiationForOverloadFailure(node, typeParameters, candidate, args, checkMode);
Comment on lines +36885 to +36886

@Andarist Mateusz Burzyński (Andarist) Jun 6, 2025

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I'd consider revisiting this in Corsa where CallState is already inroduced and improving upon this would likely be slightly easier thanks to that

@jakebailey Jake Bailey (jakebailey) Dec 4, 2025

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Could you be convinced to try and port this to Corsa now, just to see?

@Andarist Mateusz Burzyński (Andarist) Dec 4, 2025

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Have I ever come as hard to convince kind of a guy? 😂

candidates[bestIndex] = instantiated;
return instantiated;
Expand Down
16 changes: 9 additions & 7 deletions tests/baselines/reference/contextualSignatureInstantiation.errors.txt
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@@ -1,12 +1,12 @@
contextualSignatureInstantiation.ts(19,5): error TS2403: Subsequent variable declarations must have the same type. Variable 'b' must be of type 'string | number', but here has type 'unknown'.
contextualSignatureInstantiation.ts(19,5): error TS2403: Subsequent variable declarations must have the same type. Variable 'b' must be of type 'string | number', but here has type 'number'.
contextualSignatureInstantiation.ts(19,13): error TS2345: Argument of type '<T>(x: T, y: T) => T' is not assignable to parameter of type '(x: number, y: string) => number'.
Types of parameters 'y' and 'y' are incompatible.
Type 'string' is not assignable to type 'number'.
contextualSignatureInstantiation.ts(20,5): error TS2403: Subsequent variable declarations must have the same type. Variable 'b' must be of type 'string | number', but here has type 'unknown'.
contextualSignatureInstantiation.ts(20,5): error TS2403: Subsequent variable declarations must have the same type. Variable 'b' must be of type 'string | number', but here has type 'number'.
contextualSignatureInstantiation.ts(20,23): error TS2345: Argument of type '<T>(x: T, y: T) => T' is not assignable to parameter of type '(x: number, y: string) => number'.
Types of parameters 'y' and 'y' are incompatible.
Type 'string' is not assignable to type 'number'.
contextualSignatureInstantiation.ts(21,5): error TS2403: Subsequent variable declarations must have the same type. Variable 'b' must be of type 'string | number', but here has type 'unknown'.
contextualSignatureInstantiation.ts(21,5): error TS2403: Subsequent variable declarations must have the same type. Variable 'b' must be of type 'string | number', but here has type 'string'.
contextualSignatureInstantiation.ts(21,23): error TS2345: Argument of type '<T>(x: T, y: T) => T' is not assignable to parameter of type '(x: string, y: number) => string'.
Types of parameters 'y' and 'y' are incompatible.
Type 'number' is not assignable to type 'string'.
Expand All @@ -33,29 +33,31 @@ contextualSignatureInstantiation.ts(21,23): error TS2345: Argument of type '<T>(
var b: number | string;
var b = foo(g); // Error, number and string are disjoint types
~
!!! error TS2403: Subsequent variable declarations must have the same type. Variable 'b' must be of type 'string | number', but here has type 'unknown'.
!!! error TS2403: Subsequent variable declarations must have the same type. Variable 'b' must be of type 'string | number', but here has type 'number'.
!!! related TS6203 contextualSignatureInstantiation.ts:18:5: 'b' was also declared here.
~
!!! error TS2345: Argument of type '<T>(x: T, y: T) => T' is not assignable to parameter of type '(x: number, y: string) => number'.
!!! error TS2345: Types of parameters 'y' and 'y' are incompatible.
!!! error TS2345: Type 'string' is not assignable to type 'number'.
var b = bar(1, "one", g); // Error, number and string are disjoint types
~
!!! error TS2403: Subsequent variable declarations must have the same type. Variable 'b' must be of type 'string | number', but here has type 'unknown'.
!!! error TS2403: Subsequent variable declarations must have the same type. Variable 'b' must be of type 'string | number', but here has type 'number'.
!!! related TS6203 contextualSignatureInstantiation.ts:18:5: 'b' was also declared here.
~
!!! error TS2345: Argument of type '<T>(x: T, y: T) => T' is not assignable to parameter of type '(x: number, y: string) => number'.
!!! error TS2345: Types of parameters 'y' and 'y' are incompatible.
!!! error TS2345: Type 'string' is not assignable to type 'number'.
var b = bar("one", 1, g); // Error, number and string are disjoint types
~
!!! error TS2403: Subsequent variable declarations must have the same type. Variable 'b' must be of type 'string | number', but here has type 'unknown'.
!!! error TS2403: Subsequent variable declarations must have the same type. Variable 'b' must be of type 'string | number', but here has type 'string'.
!!! related TS6203 contextualSignatureInstantiation.ts:18:5: 'b' was also declared here.
~
!!! error TS2345: Argument of type '<T>(x: T, y: T) => T' is not assignable to parameter of type '(x: string, y: number) => string'.
!!! error TS2345: Types of parameters 'y' and 'y' are incompatible.
!!! error TS2345: Type 'number' is not assignable to type 'string'.
var b = baz(b, b, g); // Should be number | string

var b2: number | string;
var b2 = baz(b2, b2, g); // Should be number | string

var d: number[] | string[];
var d = foo(h); // Should be number[] | string[]
Expand Down
7 changes: 5 additions & 2 deletions tests/baselines/reference/contextualSignatureInstantiation.js
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Expand Up @@ -22,7 +22,9 @@ var b: number | string;
var b = foo(g); // Error, number and string are disjoint types
var b = bar(1, "one", g); // Error, number and string are disjoint types
var b = bar("one", 1, g); // Error, number and string are disjoint types
var b = baz(b, b, g); // Should be number | string

var b2: number | string;
var b2 = baz(b2, b2, g); // Should be number | string

var d: number[] | string[];
var d = foo(h); // Should be number[] | string[]
Expand All @@ -44,7 +46,8 @@ var b;
var b = foo(g); // Error, number and string are disjoint types
var b = bar(1, "one", g); // Error, number and string are disjoint types
var b = bar("one", 1, g); // Error, number and string are disjoint types
var b = baz(b, b, g); // Should be number | string
var b2;
var b2 = baz(b2, b2, g); // Should be number | string
var d;
var d = foo(h); // Should be number[] | string[]
var d = bar(1, "one", h); // Should be number[] | string[]
Expand Down
33 changes: 18 additions & 15 deletions tests/baselines/reference/contextualSignatureInstantiation.symbols
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Expand Up @@ -83,52 +83,55 @@ var a = baz(1, 1, g); // Should be number
>g : Symbol(g, Decl(contextualSignatureInstantiation.ts, 8, 65))

var b: number | string;
>b : Symbol(b, Decl(contextualSignatureInstantiation.ts, 17, 3), Decl(contextualSignatureInstantiation.ts, 18, 3), Decl(contextualSignatureInstantiation.ts, 19, 3), Decl(contextualSignatureInstantiation.ts, 20, 3), Decl(contextualSignatureInstantiation.ts, 21, 3))
>b : Symbol(b, Decl(contextualSignatureInstantiation.ts, 17, 3), Decl(contextualSignatureInstantiation.ts, 18, 3), Decl(contextualSignatureInstantiation.ts, 19, 3), Decl(contextualSignatureInstantiation.ts, 20, 3))

var b = foo(g); // Error, number and string are disjoint types
>b : Symbol(b, Decl(contextualSignatureInstantiation.ts, 17, 3), Decl(contextualSignatureInstantiation.ts, 18, 3), Decl(contextualSignatureInstantiation.ts, 19, 3), Decl(contextualSignatureInstantiation.ts, 20, 3), Decl(contextualSignatureInstantiation.ts, 21, 3))
>b : Symbol(b, Decl(contextualSignatureInstantiation.ts, 17, 3), Decl(contextualSignatureInstantiation.ts, 18, 3), Decl(contextualSignatureInstantiation.ts, 19, 3), Decl(contextualSignatureInstantiation.ts, 20, 3))
>foo : Symbol(foo, Decl(contextualSignatureInstantiation.ts, 0, 0))
>g : Symbol(g, Decl(contextualSignatureInstantiation.ts, 8, 65))

var b = bar(1, "one", g); // Error, number and string are disjoint types
>b : Symbol(b, Decl(contextualSignatureInstantiation.ts, 17, 3), Decl(contextualSignatureInstantiation.ts, 18, 3), Decl(contextualSignatureInstantiation.ts, 19, 3), Decl(contextualSignatureInstantiation.ts, 20, 3), Decl(contextualSignatureInstantiation.ts, 21, 3))
>b : Symbol(b, Decl(contextualSignatureInstantiation.ts, 17, 3), Decl(contextualSignatureInstantiation.ts, 18, 3), Decl(contextualSignatureInstantiation.ts, 19, 3), Decl(contextualSignatureInstantiation.ts, 20, 3))
>bar : Symbol(bar, Decl(contextualSignatureInstantiation.ts, 6, 60))
>g : Symbol(g, Decl(contextualSignatureInstantiation.ts, 8, 65))

var b = bar("one", 1, g); // Error, number and string are disjoint types
>b : Symbol(b, Decl(contextualSignatureInstantiation.ts, 17, 3), Decl(contextualSignatureInstantiation.ts, 18, 3), Decl(contextualSignatureInstantiation.ts, 19, 3), Decl(contextualSignatureInstantiation.ts, 20, 3), Decl(contextualSignatureInstantiation.ts, 21, 3))
>b : Symbol(b, Decl(contextualSignatureInstantiation.ts, 17, 3), Decl(contextualSignatureInstantiation.ts, 18, 3), Decl(contextualSignatureInstantiation.ts, 19, 3), Decl(contextualSignatureInstantiation.ts, 20, 3))
>bar : Symbol(bar, Decl(contextualSignatureInstantiation.ts, 6, 60))
>g : Symbol(g, Decl(contextualSignatureInstantiation.ts, 8, 65))

var b = baz(b, b, g); // Should be number | string
>b : Symbol(b, Decl(contextualSignatureInstantiation.ts, 17, 3), Decl(contextualSignatureInstantiation.ts, 18, 3), Decl(contextualSignatureInstantiation.ts, 19, 3), Decl(contextualSignatureInstantiation.ts, 20, 3), Decl(contextualSignatureInstantiation.ts, 21, 3))
var b2: number | string;
>b2 : Symbol(b2, Decl(contextualSignatureInstantiation.ts, 22, 3), Decl(contextualSignatureInstantiation.ts, 23, 3))

var b2 = baz(b2, b2, g); // Should be number | string
>b2 : Symbol(b2, Decl(contextualSignatureInstantiation.ts, 22, 3), Decl(contextualSignatureInstantiation.ts, 23, 3))
>baz : Symbol(baz, Decl(contextualSignatureInstantiation.ts, 7, 68))
>b : Symbol(b, Decl(contextualSignatureInstantiation.ts, 17, 3), Decl(contextualSignatureInstantiation.ts, 18, 3), Decl(contextualSignatureInstantiation.ts, 19, 3), Decl(contextualSignatureInstantiation.ts, 20, 3), Decl(contextualSignatureInstantiation.ts, 21, 3))
>b : Symbol(b, Decl(contextualSignatureInstantiation.ts, 17, 3), Decl(contextualSignatureInstantiation.ts, 18, 3), Decl(contextualSignatureInstantiation.ts, 19, 3), Decl(contextualSignatureInstantiation.ts, 20, 3), Decl(contextualSignatureInstantiation.ts, 21, 3))
>b2 : Symbol(b2, Decl(contextualSignatureInstantiation.ts, 22, 3), Decl(contextualSignatureInstantiation.ts, 23, 3))
>b2 : Symbol(b2, Decl(contextualSignatureInstantiation.ts, 22, 3), Decl(contextualSignatureInstantiation.ts, 23, 3))
>g : Symbol(g, Decl(contextualSignatureInstantiation.ts, 8, 65))

var d: number[] | string[];
>d : Symbol(d, Decl(contextualSignatureInstantiation.ts, 23, 3), Decl(contextualSignatureInstantiation.ts, 24, 3), Decl(contextualSignatureInstantiation.ts, 25, 3), Decl(contextualSignatureInstantiation.ts, 26, 3), Decl(contextualSignatureInstantiation.ts, 27, 3))
>d : Symbol(d, Decl(contextualSignatureInstantiation.ts, 25, 3), Decl(contextualSignatureInstantiation.ts, 26, 3), Decl(contextualSignatureInstantiation.ts, 27, 3), Decl(contextualSignatureInstantiation.ts, 28, 3), Decl(contextualSignatureInstantiation.ts, 29, 3))

var d = foo(h); // Should be number[] | string[]
>d : Symbol(d, Decl(contextualSignatureInstantiation.ts, 23, 3), Decl(contextualSignatureInstantiation.ts, 24, 3), Decl(contextualSignatureInstantiation.ts, 25, 3), Decl(contextualSignatureInstantiation.ts, 26, 3), Decl(contextualSignatureInstantiation.ts, 27, 3))
>d : Symbol(d, Decl(contextualSignatureInstantiation.ts, 25, 3), Decl(contextualSignatureInstantiation.ts, 26, 3), Decl(contextualSignatureInstantiation.ts, 27, 3), Decl(contextualSignatureInstantiation.ts, 28, 3), Decl(contextualSignatureInstantiation.ts, 29, 3))
>foo : Symbol(foo, Decl(contextualSignatureInstantiation.ts, 0, 0))
>h : Symbol(h, Decl(contextualSignatureInstantiation.ts, 10, 37))

var d = bar(1, "one", h); // Should be number[] | string[]
>d : Symbol(d, Decl(contextualSignatureInstantiation.ts, 23, 3), Decl(contextualSignatureInstantiation.ts, 24, 3), Decl(contextualSignatureInstantiation.ts, 25, 3), Decl(contextualSignatureInstantiation.ts, 26, 3), Decl(contextualSignatureInstantiation.ts, 27, 3))
>d : Symbol(d, Decl(contextualSignatureInstantiation.ts, 25, 3), Decl(contextualSignatureInstantiation.ts, 26, 3), Decl(contextualSignatureInstantiation.ts, 27, 3), Decl(contextualSignatureInstantiation.ts, 28, 3), Decl(contextualSignatureInstantiation.ts, 29, 3))
>bar : Symbol(bar, Decl(contextualSignatureInstantiation.ts, 6, 60))
>h : Symbol(h, Decl(contextualSignatureInstantiation.ts, 10, 37))

var d = bar("one", 1, h); // Should be number[] | string[]
>d : Symbol(d, Decl(contextualSignatureInstantiation.ts, 23, 3), Decl(contextualSignatureInstantiation.ts, 24, 3), Decl(contextualSignatureInstantiation.ts, 25, 3), Decl(contextualSignatureInstantiation.ts, 26, 3), Decl(contextualSignatureInstantiation.ts, 27, 3))
>d : Symbol(d, Decl(contextualSignatureInstantiation.ts, 25, 3), Decl(contextualSignatureInstantiation.ts, 26, 3), Decl(contextualSignatureInstantiation.ts, 27, 3), Decl(contextualSignatureInstantiation.ts, 28, 3), Decl(contextualSignatureInstantiation.ts, 29, 3))
>bar : Symbol(bar, Decl(contextualSignatureInstantiation.ts, 6, 60))
>h : Symbol(h, Decl(contextualSignatureInstantiation.ts, 10, 37))

var d = baz(d, d, g); // Should be number[] | string[]
>d : Symbol(d, Decl(contextualSignatureInstantiation.ts, 23, 3), Decl(contextualSignatureInstantiation.ts, 24, 3), Decl(contextualSignatureInstantiation.ts, 25, 3), Decl(contextualSignatureInstantiation.ts, 26, 3), Decl(contextualSignatureInstantiation.ts, 27, 3))
>d : Symbol(d, Decl(contextualSignatureInstantiation.ts, 25, 3), Decl(contextualSignatureInstantiation.ts, 26, 3), Decl(contextualSignatureInstantiation.ts, 27, 3), Decl(contextualSignatureInstantiation.ts, 28, 3), Decl(contextualSignatureInstantiation.ts, 29, 3))
>baz : Symbol(baz, Decl(contextualSignatureInstantiation.ts, 7, 68))
>d : Symbol(d, Decl(contextualSignatureInstantiation.ts, 23, 3), Decl(contextualSignatureInstantiation.ts, 24, 3), Decl(contextualSignatureInstantiation.ts, 25, 3), Decl(contextualSignatureInstantiation.ts, 26, 3), Decl(contextualSignatureInstantiation.ts, 27, 3))
>d : Symbol(d, Decl(contextualSignatureInstantiation.ts, 23, 3), Decl(contextualSignatureInstantiation.ts, 24, 3), Decl(contextualSignatureInstantiation.ts, 25, 3), Decl(contextualSignatureInstantiation.ts, 26, 3), Decl(contextualSignatureInstantiation.ts, 27, 3))
>d : Symbol(d, Decl(contextualSignatureInstantiation.ts, 25, 3), Decl(contextualSignatureInstantiation.ts, 26, 3), Decl(contextualSignatureInstantiation.ts, 27, 3), Decl(contextualSignatureInstantiation.ts, 28, 3), Decl(contextualSignatureInstantiation.ts, 29, 3))
>d : Symbol(d, Decl(contextualSignatureInstantiation.ts, 25, 3), Decl(contextualSignatureInstantiation.ts, 26, 3), Decl(contextualSignatureInstantiation.ts, 27, 3), Decl(contextualSignatureInstantiation.ts, 28, 3), Decl(contextualSignatureInstantiation.ts, 29, 3))
>g : Symbol(g, Decl(contextualSignatureInstantiation.ts, 8, 65))

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