[regression] recursive like types => maximum call stack error

[lifaon74]

TypeScript Version: 3.9.x and 4.0.0

Search Terms: maximum call stack, recursive type

Code

• source code here: https://github.com/lifaon74/observables
• yarn install, yarn run build_all

On one of my big projet, migrating from typescript 3.8.3 to 3.9.3 broke many things:

• "circular constraint" errors appeared. I need some kind of circular reference to check if a Generic type matches a specific pattern
• "maximum call stack" error when building the project (simply running tsc)

Expected behavior:
should transpile

Related Issues:
#37475
#38198

[weswigham]

The crash looks to be fixed by #38904 (meaning the crash is probably similar in nature or exactly the issue with the updated definition of Array.prototype.flat shipped in 3.9). After that it looks like you just have a lot of newly detected circularities in generic constraints, like TKVMap extends TFiniteStateKeyValueMapConstraint<TValue, TFinalState, TKVMap>, where in TFiniteStateKeyValueMapConstraint, TKVMap meaningfully is supposed to determine the output shape. IIRC, this is new because in 3.9 we now actually can flag circularities arising as a result of mapped type creation (which is how TKVMap is eventually used recursively - in a mapped type), where prior to 3.9 we'd fail to flag these (and instead silently use an empty object type). The new behavior is more complete, as previously we were essentially failing to check these constraints.

[kasperisager]

I'm seeing stack overflows for recursive types like the following in both 3.9 and nightly:

type N<T, K extends string> = T | { [P in K]: N<T, K> }[K];

type M = N<number, "M">;

Playground Link

[weswigham]

@kasperisager mind opening a new issue for yours? That's definitely a good repro of a crash distinct from the one in the OP here (which is fixed). The OP's crash was in node building, while yours is in instantiation itself.

[kasperisager]

Not at all, I'll open a new issue ASAP 👍 Thanks!