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GeezerVison is showing github.com — Use couldContainTypeVariables to short-circuit instantiateType by amcasey · Pull Request #36951 · microsoft/TypeScript

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@amcasey

@amcasey Andrew Casey (amcasey) commented Feb 21, 2020

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This is particularly impactful for large unions of string literals.

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@amcasey
Use couldContainTypeVariables to short-circuit instantiateType
a13b9c5 
This is particularly impactful for large unions of string literals.
@amcasey
Andrew Casey (amcasey) requested review from Daniel Rosenwasser (DanielRosenwasser), Anders Hejlsberg (ahejlsberg) and Wesley Wigham (weswigham) February 21, 2020 23:15
@amcasey

Andrew Casey (amcasey) commented Feb 21, 2020

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The check could be lifted out to instantiateType to short-circuit the whole call to instantiateTypeWorker, but that was about 1% slower when I ran the material-ui benchmark. Of course, 1% might be worth it for clearer code. Thoughts?
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@amcasey

Andrew Casey (amcasey) commented Feb 21, 2020

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Not running the perf test since only unions and intersections are affected.
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@amcasey

Andrew Casey (amcasey) commented Feb 21, 2020

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I intentionally made this a very narrow change. If we wanted to go broader, we could have instantiateType and couldContainTypeVariable share their tree walks (probably by having instantiateType also return whether it encountered a type variable). If we wanted to go really nuts, it could also indicate whether the instantiated type contains type variables. Thoughts?
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weswigham
Wesley Wigham (weswigham) approved these changes Feb 22, 2020
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@weswigham Wesley Wigham (weswigham) left a comment

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Considering we already have the same check in the flags & Object + objectFlags & ObjectFlags.Anonymous case, adding this check seems fine. We can at least start with this and iterate if we need to.

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@amcasey

Andrew Casey (amcasey) commented Feb 22, 2020

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Wesley Wigham (@weswigham) I was surprised that the value didn't seem to be cached in that case. I think it will be as of #36947.
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@amcasey
Andrew Casey (amcasey) merged commit 865c120 into microsoft:master Feb 25, 2020
@amcasey
Andrew Casey (amcasey) deleted the InstantiateCouldContain branch February 25, 2020 01:50
@weswigham Wesley Wigham (weswigham) mentioned this pull request Apr 7, 2020
"Type instantiation is excessively deep and possibly infinite." for big keyof types #35493
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@microsoft Microsoft (microsoft) locked as resolved and limited conversation to collaborators Oct 21, 2025
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@weswigham Wesley Wigham (weswigham) weswigham approved these changes
@DanielRosenwasser Daniel Rosenwasser (DanielRosenwasser) Awaiting requested review from DanielRosenwasser
@ahejlsberg Anders Hejlsberg (ahejlsberg) Awaiting requested review from ahejlsberg

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2 participants

@amcasey @weswigham
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