Bail on 0- and 1-length lists in removeSubtypes to avoid spurious circularity problems
#46981
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removeSubtypes to avoid spurious circularity problemsremoveSubtypes to avoid spurious circularity problems
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This code has a type circularity that previously went undetected. Adding an `as Wizard` assertion here removes the circularity. See microsoft/TypeScript#46939 / microsoft/TypeScript#46981
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@typescript-bot perf test this |
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Heya @RyanCavanaugh, I've started to run the perf test suite on this PR at dd91ab7. You can monitor the build here. Update: The results are in! |
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@RyanCavanaugh Here they are:Comparison Report - main..46981
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I'm want to merge this, because I think the early bail is fine to have regardless of anything else, however I think there's another underlying issue that probably needs fixing, so it'd be nice if we had a tweaked example that still triggered an issue and an issue to track fixing it. Likely something like type Box = {
content?: Foo | Box
};
declare const b: Box;
class Foo {
get foo() {
return {
content: this as Foo | Box,
...b
};
}
}will continue to trigger a new-ish circularity error. |
weswigham
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Mar 5, 2022
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Creates a reasonable workaround for #46939
Another example for illustration:
When resolving the type of
Foo#foo, we need to compute the type of the object literal in the return position. This has two parts: thecontentfrom thecontent:property (typeFoo), and thecontentproperty from typeBox(which isFoo | missing).We want the type of
contenthere to be subtype-reduced when creating the union of the two possible constituents,FooandFoo. That list gets deduped ingetUnionTypeto just[Foo], then passed toremoveSubTypes, which computes this value ahead of thewhileloop below it which in reality runs zero iterations:That call to
resolveStructuredTypeMembersattempts to resolve the type ofFoo#foo, triggering a circularity even though none actually exists.Instead we can just bail out earlier in the function, saving time (I hope?) and avoiding this computation until later when doing so won't introduce a circularity.