Defer simplification of conditionals on deferred type references #37423
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@typescript-bot perf test this |
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Heya @weswigham, I've started to run the perf test suite on this PR at ea74958. You can monitor the build here. |
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Fixes #37344
When we started "normalizing" deferred type aliases at the start of comparisons (#35266), we started to eagerly pull on them when we constructed conditional types around them (as conditionals eagerly check to see if they can simplify to their branches in some cases), which means that that normalization actually broke some very common patterns (like the generic action alias in the linked issue). To avoid that break, while still performing that normalization, in this PR, we now unconditionally defer conditionals where the check or extends type is itself a deferred type reference, and then later on perform the simplification of the conditional as part of
getReducedType(introduced in #36696), so that deferral isn't witnessed by most consumers of the type.