microsoft / microsoft/TypeScript-TmLanguage

TSX Default Generic Arrow Function Syntax Highlighting

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Dominant language
TypeScript
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Description

Does this issue occur when all extensions are disabled?: Yes

  • VS Code Version: Version: 1.78.2
  • OS Version: Darwin arm64 21.3.0

Related to https://github.com/microsoft/TypeScript/issues/47062
TSC has been updated to successfully parse the below TSX code snippet:

const Component = <T = undefined>(props: PropType<T>) => <p>content</p>

however this currently breaks the syntax highlighting in VSCode's typescriptreact parser.

The same can be said for the trailing comma added by prettier (3.0.3):

const Component = <T = undefined,>(props: PropType<T>) => <p>content</p>

Some short term work-arounds are available:

Using extends

const Component = <T extends unknown = undefined>(props: PropType<T>) => <p>content</p>

Using function syntax

const Component = function<T = undefined>(props: PropType<T>) {
  return <p>content</p>
}

Despite these workarounds, the original code seems syntactically valid, and more concise, so I believe this to be a bug

Contributor guide

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Reproduce the two generic-arrow-function snippets in VS Code with the typescriptreact parser and compare their highlighting with the workaround examples. Then inspect the repository's TextMate grammar files for the TypeScript JSX rules; done means both valid forms highlight correctly without regressing the shown workarounds.

Written by the indexing model from the issue text.

Assessment

Tech stack
typescript
Domain
tooling
Issue type
Bug
Difficulty
3/5
Estimated time
1-2 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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