Crash: TypeError: Cannot read properties of undefined (reading 'aliasSymbol') remains when using variadic tuple with (infer C)[] and constrained infer

[na7ure-a]

🔎 Search Terms

aliasSymbol, inferFromTypes, variadic tuple, compiler crash

🕗 Version & Regression Information

Version: 5.7.3, 5.8.3, 5.9.3,nightly (Still crashing after PR for #63014 )

⏯ Playground Link

https://www.typescriptlang.org/zh/play/?target=7&ts=5.9.3#code/C4TwDgpgBAygrgIwCpzAHiQPigXikqCAD2AgDsATAZygG0AoKJqAOjYAoBLMgMwgCcoAYQCUtALoAaRszYtufQQCFCJctToBDMiElRtIcfXFQA-FBUAuKGQgA3AQG56oSPn6cA5p4G5YiFHRaAEY9ACZxTEcgA

💻 Code

type SubTup<T> = T extends [
    ...(infer C)[],
    ...infer B extends [any, any]
] ? B : never;
type Trigger = SubTup<[1, 2]>;

🙁 Actual behavior

TypeError: Cannot read properties of undefined (reading 'aliasSymbol')
    at inferFromTypes (D:\github\TypeScript\built\local\_tsc.js:68686:18)
    at inferFromObjectTypes (D:\github\TypeScript\built\local\_tsc.js:69171:23)
    at invokeOnce (D:\github\TypeScript\built\local\_tsc.js:68878:9)
    at inferFromTypes (D:\github\TypeScript\built\local\_tsc.js:68840:11)
    at inferTypes (D:\github\TypeScript\built\local\_tsc.js:68674:5)
    at getConditionalType (D:\github\TypeScript\built\local\_tsc.js:62706:11)
    at getConditionalTypeInstantiation (D:\github\TypeScript\built\local\_tsc.js:63695:307)
    at instantiateTypeWorker (D:\github\TypeScript\built\local\_tsc.js:63798:14)
    at instantiateTypeWithAlias (D:\github\TypeScript\built\local\_tsc.js:63735:20)
    at getTypeAliasInstantiation (D:\github\TypeScript\built\local\_tsc.js:60300:52)

Node.js v22.19.0

🙂 Expected behavior

The compiler should not crash.

Additional information about the issue

I noticed that while PR #63014 fixed some crashes related to variadic tuples, the compiler still crashes (ICE) when using a slightly different syntax.

[RyanCavanaugh]

Crashes in TS7 as well

[Andarist]

Im pretty sure #63014 fixes this and this issue is a duplicate of #63005

[na7ure-a]

Hi @Andarist, thanks for looking into this!

I tested this locally by applying your fix from #63014 onto a clean origin/main and rebuilding the compiler — the crash in #63005 is indeed fixed, but the code snippet in this issue still crashes. Could you maybe give it a try with the exact code from this issue?

Thanks for all your work on these crash fixes!

[Andarist]

Ah, sorry for jumping to the wrong conclusion! I have not read the whole thread carefully and the repro was really really similar to the other one 😅 I would probably still call this a duplicate(-ish) of that other issue. It points to the same kind of deficiencies in the very same part of the algorithm. Nevertheless, I'm super glad you have raised this issue as my PR, clearly, missed those cases. I just pushed out the fix for this to the same PR.

[RyanCavanaugh]

I don't think we want to take this PR for TS 6 given the apparent delicacy of this general area, unless we're seeing this in "real" codebases (correct me if I'm wrong but @na7ure-a seems to be doing some kind of fuzzing activity to try to find these, which is appreciated but not indicative as to priority)