Don't eagerly simplify reducible generic union index types #46812
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typescript-bot
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@typescript-bot perf test this |
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Heya @andrewbranch, I've started to run the perf test suite on this PR at 43bfe00. You can monitor the build here. Update: The results are in! |
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Heya @andrewbranch, I've started to run the inline community code test suite on this PR at 43bfe00. You can monitor the build here. Update: The results are in! |
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Heya @andrewbranch, I've started to run the parallelized Definitely Typed test suite on this PR at 43bfe00. You can monitor the build here. |
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@andrewbranch |
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@andrewbranch Here they are:Comparison Report - main..46812
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All the extended CI results and perf look fine. Reviews please~ |
andrewbranch
approved these changes
Nov 16, 2021
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@weswigham Is this ready? Does it need another review? I just noticed it when going through the Needs Merge column of the PR backlog. |
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Fixes #45530
The issue wasn't that the mapped types were losing information, per sey, in fact, they were responsible for rehydrating missing information in some instances - instead, the issue was that we were too eagerly reducing the
keyofresult of unions over types which might have been reduced upon instantiation, like({v: T} & {v: "a", a: string}) | ({v: T} & {v: "b", b: string}). Before this change,keyofthat was just"v", while now it will remain the generickeyof (({v: T} & {v: "a", a: string}) | ({v: T} & {v: "b", b: string})), since instantiation can make it simplify to eitherkeyof ({v: "a"} & {v: "a", a: string})orkeyof ({v: "b"} & {v: "b", b: string}), which have keys"v" | "a"or"v" | "b", respectively. (Which in turn trickles down to assignability behavior of mapped types over those kinds ofkeyoftypes)