Don't cache child lists for tokens #58233
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…all child-lists as readonly arrays.
typescript-bot
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Author: Team
For Uncommitted Bug
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@typescript-bot perf test this |
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Looks like you're introducing a change to the public API surface area. If this includes breaking changes, please document them on our wiki's API Breaking Changes page. Also, please make sure @DanielRosenwasser and @RyanCavanaugh are aware of the changes, just as a heads up. |
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I guess an alternative path would be to have |
rbuckton
reviewed
Apr 17, 2024
src/compiler/factory/nodeChildren.ts
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| const nodeChildren = new WeakMap<Node, Node[] | undefined>(); | ||
| const nodeChildren = new WeakMap<Node, readonly Node[] | undefined>(); | ||
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| const emptyChildren: readonly Node[] = Object.freeze([]); |
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Confusingly, services defines its own mutable empty array (and none of them actually guard against modification)
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Oh, this isn't even in services, yeah, emptyArray would be nice. (I used to have a PR that froze it but it didn't really seem to matter)
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From the description:
If we want, we can probably just use the internal
emptyArray, but I don't think we've ever frozen that one.
Happy to switch over to that too, but Jake mentioned that he didn't want to make that change since getChildren() always was declared as a mutable array. Freezing this array (for runtime safety) and propagating the change (for static verification) helped validate that it's unlikely we mutate these arrays.
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Does freezing emptyArray affect our perf at all? If not, I'd just do that and use emptyArray.
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it sure looks like freezing is bad: #58240 (comment)
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@typescript-bot test top400 |
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@DanielRosenwasser Here they are:
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@DanielRosenwasser Here are the results of running the top 400 repos comparing Everything looks good! |
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@typescript-bot perf test this |
DanielRosenwasser
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getNodeChildren
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@DanielRosenwasser Here they are:
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It turns out that we always made this optimization - the only difference with this PR is that now
I don't know if there is a difference practically between |
DanielRosenwasser
added
Breaking Change
They're equivalent in behavior, but But yes, better to not stick that empty array into the weak map over and over. |
rbuckton
approved these changes
Apr 19, 2024
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This PR always returns a shared frozen array from
getNodeChildrenwhen given a token (e.g. an identifier or any other keyword, punctuation, etc.). It also marks all child-lists asreadonly Node[]instead of justNode[].If we want, we can probably just use the internal
emptyArray, but I don't think we've ever frozen that one.