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Fix compiler crash on generics overload resolution failure #62790

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Fix compiler crash on generics overload resolution failure #62790

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2bc8933
Add reproduction test case for #61524
moznion Nov 21, 2025
56578c5
Fix compiler crash on generics overload resolution failure reported b…
moznion Nov 20, 2025
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35 changes: 33 additions & 2 deletions src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -36603,7 +36603,22 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
}
}
else {
Debug.fail("No error for last overload signature");
// Fallback: Generate a generic error when no specific error can be determined
// This replaces the Debug.fail() to prevent compiler crashes
// See: https://github.com/microsoft/TypeScript/issues/61524
const fallbackChain = chainDiagnosticMessages(
/*details*/ undefined,
Diagnostics.No_overload_matches_this_call,
);
const errorNode = getErrorNodeForCallNode(node);
const fallbackDiag = createDiagnosticForNodeFromMessageChain(
getSourceFileOfNode(errorNode),
errorNode,
fallbackChain,
/*relatedInformation*/ undefined,
);

diagnostics.add(fallbackDiag);
}
}
else {
Expand All @@ -36624,7 +36639,23 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
allDiagnostics.push(diags);
}
else {
Debug.fail("No error for 3 or fewer overload signatures");
// Fallback: Generate a generic error for this overload candidate
// This prevents crashes when processing multiple overload signatures
const fallbackChain = chainDiagnosticMessages(
/*details*/ undefined,
Diagnostics.Overload_0_of_1_2_gave_the_following_error,
i + 1,
candidates.length,
signatureToString(c),
);
const errorNode = getErrorNodeForCallNode(node);
const fallbackDiag = createDiagnosticForNodeFromMessageChain(
getSourceFileOfNode(errorNode),
errorNode,
fallbackChain,
/*relatedInformation*/ undefined,
);
allDiagnostics.push([fallbackDiag]);
}
i++;
}
Expand Down
28 changes: 28 additions & 0 deletions tests/baselines/reference/issue61524DebugFailureCrash.errors.txt
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@@ -0,0 +1,28 @@
issue61524DebugFailureCrash.ts(10,37): error TS2550: Property 'entries' does not exist on type 'ObjectConstructor'. Do you need to change your target library? Try changing the 'lib' compiler option to 'es2017' or later.
issue61524DebugFailureCrash.ts(11,9): error TS2769: No overload matches this call.


==== issue61524DebugFailureCrash.ts (2 errors) ====
// Exact reproduction from https://github.com/microsoft/TypeScript/issues/61524
// This code causes "Debug Failure. No error for last overload signature"

type Generic<T> = T extends any[] ? T[number] : T[keyof T];

export function testFn<A extends Record<string, any>>(
obj: A,
cb: (b: Generic<Partial<A>>) => any
) {
for (const [key, val] of Object.entries(obj)) {
~~~~~~~
!!! error TS2550: Property 'entries' does not exist on type 'ObjectConstructor'. Do you need to change your target library? Try changing the 'lib' compiler option to 'es2017' or later.
cb(val as Generic<A>);
~~
!!! error TS2769: No overload matches this call.
}
}

// Usage that triggers the crash
testFn(
{ foo: "bar", num: 42 },
(val) => console.log(val) // Type inference here causes the issue
);
61 changes: 61 additions & 0 deletions tests/baselines/reference/issue61524DebugFailureCrash.symbols
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@@ -0,0 +1,61 @@
//// [tests/cases/compiler/issue61524DebugFailureCrash.ts] ////

=== issue61524DebugFailureCrash.ts ===
// Exact reproduction from https://github.com/microsoft/TypeScript/issues/61524
// This code causes "Debug Failure. No error for last overload signature"

type Generic<T> = T extends any[] ? T[number] : T[keyof T];
>Generic : Symbol(Generic, Decl(issue61524DebugFailureCrash.ts, 0, 0))
>T : Symbol(T, Decl(issue61524DebugFailureCrash.ts, 3, 13))
>T : Symbol(T, Decl(issue61524DebugFailureCrash.ts, 3, 13))
>T : Symbol(T, Decl(issue61524DebugFailureCrash.ts, 3, 13))
>T : Symbol(T, Decl(issue61524DebugFailureCrash.ts, 3, 13))
>T : Symbol(T, Decl(issue61524DebugFailureCrash.ts, 3, 13))

export function testFn<A extends Record<string, any>>(
>testFn : Symbol(testFn, Decl(issue61524DebugFailureCrash.ts, 3, 59))
>A : Symbol(A, Decl(issue61524DebugFailureCrash.ts, 5, 23))
>Record : Symbol(Record, Decl(lib.es5.d.ts, --, --))

obj: A,
>obj : Symbol(obj, Decl(issue61524DebugFailureCrash.ts, 5, 54))
>A : Symbol(A, Decl(issue61524DebugFailureCrash.ts, 5, 23))

cb: (b: Generic<Partial<A>>) => any
>cb : Symbol(cb, Decl(issue61524DebugFailureCrash.ts, 6, 11))
>b : Symbol(b, Decl(issue61524DebugFailureCrash.ts, 7, 9))
>Generic : Symbol(Generic, Decl(issue61524DebugFailureCrash.ts, 0, 0))
>Partial : Symbol(Partial, Decl(lib.es5.d.ts, --, --))
>A : Symbol(A, Decl(issue61524DebugFailureCrash.ts, 5, 23))

) {
for (const [key, val] of Object.entries(obj)) {
>key : Symbol(key, Decl(issue61524DebugFailureCrash.ts, 9, 16))
>val : Symbol(val, Decl(issue61524DebugFailureCrash.ts, 9, 20))
>Object : Symbol(Object, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
>obj : Symbol(obj, Decl(issue61524DebugFailureCrash.ts, 5, 54))

cb(val as Generic<A>);
>cb : Symbol(cb, Decl(issue61524DebugFailureCrash.ts, 6, 11))
>val : Symbol(val, Decl(issue61524DebugFailureCrash.ts, 9, 20))
>Generic : Symbol(Generic, Decl(issue61524DebugFailureCrash.ts, 0, 0))
>A : Symbol(A, Decl(issue61524DebugFailureCrash.ts, 5, 23))
}
}

// Usage that triggers the crash
testFn(
>testFn : Symbol(testFn, Decl(issue61524DebugFailureCrash.ts, 3, 59))

{ foo: "bar", num: 42 },
>foo : Symbol(foo, Decl(issue61524DebugFailureCrash.ts, 16, 5))
>num : Symbol(num, Decl(issue61524DebugFailureCrash.ts, 16, 17))

(val) => console.log(val) // Type inference here causes the issue
>val : Symbol(val, Decl(issue61524DebugFailureCrash.ts, 17, 5))
>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
>val : Symbol(val, Decl(issue61524DebugFailureCrash.ts, 17, 5))

);
89 changes: 89 additions & 0 deletions tests/baselines/reference/issue61524DebugFailureCrash.types
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@@ -0,0 +1,89 @@
//// [tests/cases/compiler/issue61524DebugFailureCrash.ts] ////

=== issue61524DebugFailureCrash.ts ===
// Exact reproduction from https://github.com/microsoft/TypeScript/issues/61524
// This code causes "Debug Failure. No error for last overload signature"

type Generic<T> = T extends any[] ? T[number] : T[keyof T];
>Generic : Generic<T>
> : ^^^^^^^^^^

export function testFn<A extends Record<string, any>>(
>testFn : <A extends Record<string, any>>(obj: A, cb: (b: Generic<Partial<A>>) => any) => void
> : ^ ^^^^^^^^^ ^^ ^^ ^^ ^^ ^^^^^^^^^

obj: A,
>obj : A
> : ^

cb: (b: Generic<Partial<A>>) => any
>cb : (b: Generic<Partial<A>>) => any
> : ^ ^^ ^^^^^
>b : Generic<Partial<A>>
> : ^^^^^^^^^^^^^^^^^^^

) {
for (const [key, val] of Object.entries(obj)) {
>key : any
> : ^^^
>val : any
> : ^^^
>Object.entries(obj) : any
> : ^^^
>Object.entries : any
> : ^^^
>Object : ObjectConstructor
> : ^^^^^^^^^^^^^^^^^
>entries : any
> : ^^^
>obj : A
> : ^

cb(val as Generic<A>);
>cb(val as Generic<A>) : any
> : ^^^
>cb : (b: Generic<Partial<A>>) => any
> : ^ ^^ ^^^^^
>val as Generic<A> : Generic<A>
> : ^^^^^^^^^^
>val : any
> : ^^^
}
}

// Usage that triggers the crash
testFn(
>testFn( { foo: "bar", num: 42 }, (val) => console.log(val) // Type inference here causes the issue) : void
> : ^^^^
>testFn : <A extends Record<string, any>>(obj: A, cb: (b: Generic<Partial<A>>) => any) => void
> : ^ ^^^^^^^^^ ^^ ^^ ^^ ^^ ^^^^^^^^^

{ foo: "bar", num: 42 },
>{ foo: "bar", num: 42 } : { foo: string; num: number; }
> : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>foo : string
> : ^^^^^^
>"bar" : "bar"
> : ^^^^^
>num : number
> : ^^^^^^
>42 : 42
> : ^^

(val) => console.log(val) // Type inference here causes the issue
>(val) => console.log(val) : (val: string | number | undefined) => void
> : ^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>val : string | number | undefined
> : ^^^^^^^^^^^^^^^^^^^^^^^^^^^
>console.log(val) : void
> : ^^^^
>console.log : (...data: any[]) => void
> : ^^^^ ^^ ^^^^^
>console : Console
> : ^^^^^^^
>log : (...data: any[]) => void
> : ^^^^ ^^ ^^^^^
>val : string | number | undefined
> : ^^^^^^^^^^^^^^^^^^^^^^^^^^^

);
22 changes: 22 additions & 0 deletions tests/cases/compiler/issue61524DebugFailureCrash.ts
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@@ -0,0 +1,22 @@
// @strict: true
// @noEmit: true

// Exact reproduction from https://github.com/microsoft/TypeScript/issues/61524
// This code causes "Debug Failure. No error for last overload signature"

type Generic<T> = T extends any[] ? T[number] : T[keyof T];

export function testFn<A extends Record<string, any>>(
obj: A,
cb: (b: Generic<Partial<A>>) => any
) {
for (const [key, val] of Object.entries(obj)) {
cb(val as Generic<A>);
}
}

// Usage that triggers the crash
testFn(
{ foo: "bar", num: 42 },
(val) => console.log(val) // Type inference here causes the issue
);