Fix conditional type constraint exploration + signature relations

[ahejlsberg]

Fixes #47142.

[ahejlsberg]

Adding a regression test isn't simple as the repro references multiple NPM packages.

[ahejlsberg]

To be clear, this PR fixes the repro here #47142 (comment).

[weswigham]

Individually, these two changes look fine and make sense on their face - the first skips distributive constraints for circularly constrained types, which is good, and the second expands simplified signature matching to instances of the same type reference rather than just instances if the same symbol... which it's weird that the second isn't fully encompassed by the first, which is why an example and repro would be nice, but 🤷‍♂️, looks fine enough, I suppose.

[ahejlsberg]

it's weird that the second isn't fully encompassed by the first

The change to not explore circular constraint is what fixes the stack overflow. Definitely a good change.

The signature relation change keeps us from cross-comparing incompatible signatures. Without it, as we're computing the variance for UpsertGraphMethod (which has multiple signatures), we relate a PartialModelGraph<M> to a PartialModelGraph<M>[] (all are types from the Objection.js NPM package). That then sets off a cascade of deeper and deeper nested complex combinations of conditional types, index access types, and intersections. Deep enough, I guess, that isDeeplyNestedType never sees three cycles and we eventually hit the excessive stack depth limiter.

[DanielRosenwasser]

Is this comment accurate (i.e. "same anonymous type")?

[sandersn]

On DT, this breaks knockout.mapping with

Type 'KnockoutObservable<false> | KnockoutObservable<true>' is not assignable to type 'KnockoutObservable<boolean>'

Is this expected? I'll add more detail after investigating.

Edit: Here's the rest of the stack. Pretty clear the package relied on the broader signature relation before:

Type 'KnockoutObservable<false>' is not assignable to type 'KnockoutObservable<boolean>'.
     Types of parameters 'value' and 'value' are incompatible.
       Type 'boolean' is not assignable to type 'false'.

[sandersn]

Here's a small repro. I'll file it as a separate bug so we can decide whether it's worthwhile to fix:

interface Kow<T> {
    (value: T): void;
}
declare var src: Kow<true> | Kow<false>;
var tgt: Kow<boolean> = src

[ahejlsberg]

Marking this as a breaking change since the error in #47371 is the intended behavior.