Stack overflow error when using inline mapped tuples

[danny-may]

Bug Report

🔎 Search Terms

Maximum call stack size exceeded
getMappedType

🕗 Version & Regression Information

• This is a crash
• This changed between versions 4.6.4 and 4.7.4

⏯ Playground Link

Playground link with relevant code

This is an example of a logically identical class, with the inline mapping extracted, where the compiler doesnt crash

💻 Code

class Foo<Elements extends readonly unknown[]> {
    public readonly elements: { [P in keyof Elements]: { bar: Elements[P]; } };

    public constructor(...elements: { [P in keyof Elements]: { bar: Elements[P] } }) {
        this.elements = elements;
    }

    public add(): Foo<[...Elements, 'abc']> {
        return new Foo<[...Elements, 'abc']>(...this.elements, { bar: 'abc' });
    }
}

🙁 Actual behavior

The compiler crashes with a stack overflow error

🙂 Expected behavior

Compilation should succeed with no errors. Extracting the inline mapped type to its own type definition achieves this, but the two are logically identical so the stack overflow is unexpected.

[fatcerberus]

You maniac! You blew it up! Damn you!
😆

[RyanCavanaugh]

This has been an issue since 4.0.5

Strong contender for the "crash which was oldest at the point it was first found" award of 2023.

Let me know if you're actually blocked by this (sounds like no?) and if so I'll assign it out instead of backlog.

[danny-may]

Not blocked by this, giving a name to the mapped type seems to fix this for whatever reason and to be honest ends up being more readable than having it inline. I just noticed this while doing some quick prototyping and was very confused as to why vscode stopped giving me errors all of a sudden.

[Andarist]

A more detailed call stack for those who might be interested where this happens :P

[danny-may]

Damn, I did some more playing and it looks like this has only been an issue since 4.7.4. Looks like changing versions in the playground doesnt cause errors to appear immediately. There goes my award 😢

[fatcerberus]

Normally that takes effect immediately, but since this is actually crashing the compiler, it might be taking longer to recover from or something.