Extend isEmptyAnonymousObjectType with support for non-generic mapped types
#56974
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Andarist
commented
Jan 7, 2024
| @@ -20849,7 +20849,11 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker { | |||
| } | |||
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| function isEmptyAnonymousObjectType(type: Type) { | |||
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Note that this is different from isEmptyObjectType and none of those reuse the other. Perhaps with this change, some sharing could be introduced. I tried that at first and a lot of tests failed - but I didn't bother digging into this right now.
I don't really know what's the intended use case of both. Some code comments here would be highly appreciated. I could add the. However, I'd need first to learn from the team about the different goals of those two.
Andarist
commented
Jan 7, 2024
| import { B, C, D } from './types2'; | ||
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| export class C implements Base { | ||
| a: Readonly<A> & { kind: 'a'; }; |
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This is a somewhat unfortunate change. However, it matches the behavior of plain A that is {}. In such a case, A doesn't appear in the output after the refactoring. Maybe that's an issue worth raising? The intention of the user could have been to reuse types from the interface quite literally - so when they start implementing A's members the C class automatically "receives" them.
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I agree that it might be unfortunate, but I think this change is ok. If we want to have a mechanism for preserving those kinds of intersections in refactorings and codefixes, we need it to also work for A & { kind: ... }.
Andarist
commented
Jan 7, 2024
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| verify.completions({ marker: "3", exact: [] }); | ||
| verify.completions({ marker: "4", exact: [] }); | ||
| verify.completions({ marker: "5", includes: ["a", "b", "c"] }); | ||
| verify.completions({ marker: "5", exact: [] }); |
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Since Record<never, never> is just {} with this PR those are expected here. Those unions were reduced to just string and thus concrete literal strings can no longer be suggested.
Both of those changed locations obey the rule from #49119 :
For backwards compatibility, special exceptions to the T & {} type reduction rules existing for intersections written explicitly as string & {}, number & {}, and bigint & {} (as opposed to created through instantiation of a generic type T & {}).
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How is it that this string & Record<never, never> was being preserved before? Is it because, before this PR, Record<never, never> was some mapped type and we couldn't do subtype reduction on the intersection?
I'm curious to see if this breaks people, since this is in our tests, but you're right, officially we only support string & {} explicitly written as so.
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Is it because, before this PR, Record<never, never> was some mapped type and we couldn't do subtype reduction on the intersection?
IIRC - yeah, something like that. The type was not reduced to {} so it stayed as a mapped type and that wasn't reduced. But with this change it's treated like {} so intersections containing it are way more easily reducible.
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@typescript-bot run DT |
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Heya @gabritto, I've started to run the parallelized Definitely Typed test suite on this PR at 081619e. You can monitor the build here. Update: The results are in! |
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Heya @gabritto, I've started to run the diff-based top-repos suite on this PR at 081619e. You can monitor the build here. Update: The results are in! |
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Heya @gabritto, I've started to run the diff-based user code test suite on this PR at 081619e. You can monitor the build here. Update: The results are in! |
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Heya @gabritto, I've started to run the regular perf test suite on this PR at 081619e. You can monitor the build here. Update: The results are in! |
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@gabritto Here are the results of running the user test suite comparing There were infrastructure failures potentially unrelated to your change:
Otherwise... Something interesting changed - please have a look. Details
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@gabritto Here they are:
tscComparison Report - baseline..pr
System info unknown
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tsserverComparison Report - baseline..pr
System info unknown
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startupComparison Report - baseline..pr
System info unknown
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Developer Information: |
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Hey @gabritto, the results of running the DT tests are ready. Branch only errors:Package: react-aria-live Package: react-instantsearch-native Package: reactable Package: relay-test-utils Package: react-native-modals Package: solid__react Package: react-gateway Package: react-helmet-with-visor Package: react-instantsearch-core Package: dom-css Package: react-instantsearch Package: react-switch-case Package: jest |
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@gabritto Here are the results of running the top-repos suite comparing Something interesting changed - please have a look. Details
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Seems like there are many breaks on the top repos test :/ |
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fixes #56691
This makes non-generic mapped types with
neverconstraints behave like{}(since it displays as{}). "If it looks like a duck, swims like a duck, and quacks like a duck, then it probably is a duck."