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Failure to parse some usages of Flow $Call (Unexpected token, expected ",") #758

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zipang opened this issue Nov 7, 2022 · 2 comments · Fixed by #769
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Failure to parse some usages of Flow $Call (Unexpected token, expected ",") #758

zipang opened this issue Nov 7, 2022 · 2 comments · Fixed by #769

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@zipang
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zipang commented Nov 7, 2022 •
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Sucrase fails to parse some usages of the type helper $Call inside Flow code :

Example of code failing :

// @flow

type Account = $PropertyType<
  $Call<<T>($ReadOnlyArray<T>) => T>,
  'account'
>

Demo :
@zipang zipang changed the title Fail to parse some usages of Flow $Call (Unexpected token, expected ",") Failure to parse some usages of Flow $Call (Unexpected token, expected ",") Nov 7, 2022
@alangpierce
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Thanks for reporting! I think the bug here is that << being mis-tokenized as a left-shift operator. There are already some special cases to get >> working (based off of similar special cases in Babel), and at least one << case was handled recently in https://github.com/alangpierce/sucrase/pull/716/files#diff-0221cac4ed46c5209e9fe0f67d5f903e3f2069287eedc8a8502f3906f504ac2c , but looks like this is a case that was missed.

alangpierce added a commit that referenced this issue Nov 27, 2022
@alangpierce
Fix parsing of << within a type
3d9ba6c 
Fixes #758

There was already some logic from #716 to handle cases like `f<<T>() => void>`,
where we're transitioning from a non-type context to a type context and need to
detect if `<<` is actually two open-type-parameter/argument tokens. There was a
simpler missing case, though, which is that `<<` is never allowed within a type,
so we should exit early with a simple `<` in a type context. There was already a
similar case for `>`, so this just uses the same logic for `<`. This fixes the
same issue in TS and Flow.
@alangpierce alangpierce mentioned this issue Nov 27, 2022
Merged
alangpierce added a commit that referenced this issue Nov 28, 2022
@alangpierce
Fix parsing of << within a type (#769)
473a09e 
Fixes #758

There was already some logic from #716 to handle cases like `f<<T>() => void>`, where we're transitioning from a non-type context to a type context and need to detect if `<<` is actually two open-type-parameter/argument tokens. There was a simpler missing case, though, which is that `<<` is never allowed within a type, so we should tokenize as a simple `<` in a
type context. To handle the various cases correctly, this extra logic needs to only happen for `<<`, and this PR also adds
some additional comments explaining the nuances.
@zipang
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zipang commented Nov 29, 2022

Thxx a lot ! :)

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Fix parsing of << within a type alangpierce/sucrase
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@alangpierce @zipang