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Crash: TypeError: Cannot read properties of undefined (reading 'flags') in isFreshLiteralType during recursive tuple expansion with unresolved identifiers #62974

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Crash: TypeError: Cannot read properties of undefined (reading 'flags') in isFreshLiteralType during recursive tuple expansion with unresolved identifiers#62974
Labels
BugA bug in TypeScriptDomain: CrashesUnhandled exceptions/panics with no immediate primary root cause identifiedHelp WantedYou can do this
Milestone
Backlog

Description

@na7ure-a
aowei (na7ure-a)
opened on Jan 11, 2026

🔎 Search Terms

isFreshLiteralType

Cannot read properties of undefined (reading 'flags')

getNormalizedType

"Internal Compiler Error"

"Large tuple crash"

🕗 Version & Regression Information

v5.7.3: Crashes

v5.8.3: Crashes

v5.9.3: Crashes

Nightly (6.0.0-dev.20260108): Crashes

⏯ Playground Link

https://www.typescriptlang.org/zh/play/?target=7&ts=6.0.0-dev.20260111#code/PTAECUFMAcCcHtQDMEFtQGICsAWHBOARgCgAXAT2klAFUA7AZwAsBLJUgFQFdoAbSADwdQkAB6lIdACYNQAbQB0SgIZ1ycgLoaAfKAC8oYWInTZcjnIAMGgDRKFLOkkixDylrw2gA-G4+gALlA6SAA3FwBuMkpqAFFRaFUpAGVUZV5+WG4+SAYhEXFJGXl7VXUtXQMjQtN5C2s7JUdnVw53Tx9DUAAfUHjE6VT0zOz+PLaPXSDNKIoqUGTWdgEAQQKTYpXYWGVyATLtStAACmPS2ABzBiCVgEp9XVD4Fil74yLZM5VL6-kVq1soHszRcEA09z0j2eUk64ECwTCkWi8wA4ggAO79KChVbrD6gLY7PYHGygAByeNqdC4qAARi5SQAFSmbba7VZs4lqQ5Hf4Acn4dAupCYfK871qFN8ayCaPgmIS2IEiiUK0aCkZAI0cjJ4pqxS40kgSEckBhvhVCjV9k11i8N1JZNJizYpAEjMOURAoDm1DlCuguIlrKJ+25jpZsmpdIZoGZwdkhPZSa55B5+hKqtJ9hW2t1kdAhqkxtN5tA-v6ypz2dVgKdfxrGp08IrirCq0dTO0sxi5YxlbWCYJnLDaYjQ+j9NgTILKY5oYOhwzluttZ1eo2siLJZCZdbgZXNgAxjtmHXSXI1UClIzm7L+22cVf6x6e-NRoIOOP9VGaVOjpOoJDlKw6hhwUzkgWlidJo8IUkOhAwRw9p9vKlbmOe8iaDoUTFkevDKLA1D4coDCJpyABq6QvMopDwLA+RDoaADWdDynQmikgAkhmFiAbAzYAN7EKAomgIKwpMOAqgXIIyQFvxpKxApf4uNoxwMKQhGkEEySkkUABCxr0ZAQSxLcNyUdRUi0fRAjxPhXDFvZCRJEMGQuB+eT0MwroflWSj+VxSnaDo2hKa5gxpB5WQ8GMAg+UsnBxYIlpBc6oU8t2xAAL5AA

💻 Code

// Repro from #54491
type UnshiftTuple<T extends [...any[]]> = T extends [T[0],...infer Tail] ? Tail : never;
type ExpandSmallerTuples<T extends [...any[]]> = T extends [T[0],...infer Tail] ? T | ExpandSmallerTuples<Tail> : [];
type Shift<A extends Array<any>> = ((...args: A) => void) extends (...args: [A[0], ...infer R]) => void ? R : never;
type GrowExpRev<A extends Array<any>, N extends number, P extends Array<Array<any>>> = A['length'] extends N ? A : GrowExpRev<[...A,...P[0]][N] extends undefined ? [...A,...P[0]] : A, N, Shift<P>>;
// type GrowExp<A extends Array<any>, N extends number, P extends Array<Array<any>>> = [...A, ...A][N] extends undefined ? GrowExp<[...A, ...A], N, [A, ...P]> : GrowExpRev<A, N, P>;
type GrowExp<A extends Array<any>, N extends number, P extends Array<Array<any>>> = [...A,...A][N] extends undefined ? GrowExp<[...A,crash], N, [A, ...P]> : GrowExpRev<A, N, P>;
type Tuple<T, N extends number> = number extends N ? Array<T> : N extends 0 ? [] : N extends 1 ? [T] : GrowExp<[T], N, [[]]>;
declare class ArrayValidator<T extends unknown[], I = T[number]> {
    lengthRange<S extends number, E extends number>(start: S, endBefore: E): ArrayValidator<Exclude<ExpandSmallerTuples<UnshiftTuple<[...Tuple<I, E>]>>, ExpandSmallerTuples<UnshiftTuple<[...Tuple<I, S>]>>>>;
}

🙁 Actual behavior

.\ts-versions\nightly\node_modules\.bin\tsc.cmd  .\mutated\largeTupleTypes_mutated_batch0.ts
D:\do\typeFuzz\ts-versions\nightly\node_modules\typescript\lib\_tsc.js:123166
      throw e;
      ^

TypeError: Cannot read properties of undefined (reading 'flags')
    at isFreshLiteralType (D:\do\typeFuzz\ts-versions\nightly\node_modules\typescript\lib\_tsc.js:62933:20)                                                                                              
    at getNormalizedType (D:\do\typeFuzz\ts-versions\nightly\node_modules\typescript\lib\_tsc.js:64661:17)                                                                                               
    at isRelatedTo (D:\do\typeFuzz\ts-versions\nightly\node_modules\typescript\lib\_tsc.js:65015:21)                                                                                                     
    at propertiesRelatedTo (D:\do\typeFuzz\ts-versions\nightly\node_modules\typescript\lib\_tsc.js:66695:29)                                                                                             
    at structuredTypeRelatedToWorker (D:\do\typeFuzz\ts-versions\nightly\node_modules\typescript\lib\_tsc.js:66300:21)                                                                                   
    at structuredTypeRelatedTo (D:\do\typeFuzz\ts-versions\nightly\node_modules\typescript\lib\_tsc.js:65726:21)                                                                                         
    at recursiveTypeRelatedTo (D:\do\typeFuzz\ts-versions\nightly\node_modules\typescript\lib\_tsc.js:65677:19)                                                                                          
    at isRelatedTo (D:\do\typeFuzz\ts-versions\nightly\node_modules\typescript\lib\_tsc.js:65090:122)                                                                                                    
    at typeArgumentsRelatedTo (D:\do\typeFuzz\ts-versions\nightly\node_modules\typescript\lib\_tsc.js:65508:25)                                                                                          
    at relateVariances (D:\do\typeFuzz\ts-versions\nightly\node_modules\typescript\lib\_tsc.js:66341:23)                                                                                                 

Node.js v22.19.0

🙂 Expected behavior

The compiler should not crash.

Additional information about the issue

No response

Activity

  1. Andarist commented on Jan 12, 2026

    @Andarist
    Mateusz Burzyński (Andarist)
    on Jan 12, 2026
    Contributor

    Repros with (and this doesn't depend anyhow on unresolved identifiers/error types/etc):

    type Inner<A extends any[], A2 extends [...A, boolean]> = A2;

export type Wrapper<A extends any[]> = Inner<
  A,
  [...A, boolean, boolean, boolean, boolean]
>;
  2. Ryan Cavanaugh (RyanCavanaugh)
    added
    BugA bug in TypeScript
    on Jan 12, 2026

  3. RyanCavanaugh commented on Jan 12, 2026

    @RyanCavanaugh
    Ryan Cavanaugh (RyanCavanaugh)
    on Jan 12, 2026
    Member

    Repros in TS7 as well

  4. Ryan Cavanaugh (RyanCavanaugh)
    added this to the Backlog milestone on Jan 12, 2026
  5. Ryan Cavanaugh (RyanCavanaugh)
    added
    Help WantedYou can do this
    Domain: CrashesUnhandled exceptions/panics with no immediate primary root cause identified
    on Jan 12, 2026

  6. ahejlsberg commented on Jul 24, 2026

    @ahejlsberg
    Anders Hejlsberg (ahejlsberg)
    on Jul 24, 2026
    Member

    Fixed by microsoft/typescript-go#4735.

  7. Anders Hejlsberg (ahejlsberg)
    closed this as completedon Jul 24, 2026
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