Getting recursive type errors with TS 4.3.2 when they don't happen with TS 4.2.4

[xaviergonz]

Bug Report

Given (this is just the smaller repro I could come up with, not real code):

const p = <T>(fn: () => T): T => {return null as any}

const Base = <T>(val: T): {new(): T} => {
  return null as any;
}

class C extends Base({
 x: p<C[]>(() => [])
}) { }

With TS 4.3.2 it gives the errors:

Type 'C' recursively references itself as a base type.ts(2310)
'C' is referenced directly or indirectly in its own base expression.ts(2506)

where as there's no such error with TS 4.2.4

If the p function parameter is changed from fn: () => T to fn: () => any or x: p<C[]>(() => []) is changed to x: p<C[]>(() => [] as any) then it does not give that error anymore.

Real impact:

This impacts a library that used to be able to do self-referenced models:

class TreeNode extends Model({ children: prop<TreeNode[]>(() => []), x: prop(0) }) {}

but with the new version it is not possible anymore

Alternative repro:

abstract class Base2 {
    abstract root() : Derived
}

class Derived extends class extends Base2 {
  root() {
    return undefined as any
  }
}
{}

🕗 Version & Regression Information

• This changed between versions 4.2.4 and 4.3.2

⏯ Playground Link

Playground Link

[xaviergonz]

It seems this was introduced in 4.3.0-dev.20210428 (does not happen in 4.3.0-dev.20210427).

More specifically it seems to be introduced by the addition of this line

7748694#diff-d9ab6589e714c71e657f601cf30ff51dfc607fc98419bf72e04f6b0fa92cc4b8R17241

from a commit from @andrewbranch

[xaviergonz]

More specifically the call to getBaseTypes on this line seems to trigger some side effect that causes this:

7748694#diff-d9ab6589e714c71e657f601cf30ff51dfc607fc98419bf72e04f6b0fa92cc4b8R20008

[xaviergonz]

The error seems to originate in getBaseConstructorTypeOfClass <- resolveBaseTypesOfClass <- getBaseTypes <- getSingleBaseForNonAugmentingSubtype

  if (!pushTypeResolution(type, TypeSystemPropertyName.ResolvedBaseConstructorType)) {
    return errorType;
  }

I don't think my knowledge is deep enough to dig any deeper :( but my super-wild guess is that the array related optimization in that commit is maybe trying to resolve the class structure earlier than before and therefore the cached versions cannot keep up with it

[evelant]

I think this is what's breaking my mobx-state-tree project when upgrading to TS 4.3. Not sure if this is affecting all MST projects or not but I ended up with a ton of recursive type errors after trying to update to TS 4.3.

[dsherret]

Another example showing this bug is in #44284 (I've closed that issue in favour of this one). Just like this issue, it starts happening in 4.3.0-dev.20210428.

[mrgleba]

Another repro

abstract class Base {
    abstract root() : Derived
}

class Derived extends class extends Base {
    root() {
        return undefined as any
    }
}
{   
}

[xaviergonz]

@DanielRosenwasser

[DanielRosenwasser]

Unclear if this is working as intended, but it might be a regression.

[xaviergonz]

has it been decided already if it is a regression or maybe something else?