Anonymous generator function expression with typescript generic fails to parse

[devongovett]

Bug Report

Current Behavior

Anonymous generator functions with typescript generics fail to parse:

const fn = function* <T>(input: T): Generator<number> {
  yield 2;
}

SyntaxError: Unexpected token, expected "(" (1:21)

When adding a name to the function it works as expected:

const fn = function* fn<T>(input: T): Generator<number> {
  yield 2;
}

TSC parses anonymous generator functions with generics as expected.

Input Code

• REPL

const fn = function* <T>(input: T): Generator<number> {
  yield 2;
}

Expected behavior/code

Should parse as an anonymous generator function with generic.

Additional info

Appears that the current behavior is correct for function declarations, but not function expressions. TSC throws a parse error when the function is parsed as a declaration, but not when parsed as an expression (as above).

Environment

- Babel version(s): v7.9.4
- Node/npm version: 12
- OS: macOS
- Monorepo: N/A
- How you are using Babel: `@babel/parser`

[babel-bot]

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[existentialism]

Note the error only occurs when jsx is enabled too (REPL).

[hzoo]

Good catch - later, should we just enable jsx parsing by default in the tests or run them separately?

babel/scripts/parser-tests/typescript/index.js

Line 72 in 1a08aa5

plugins: isTSX ? plugins.concat("jsx") : plugins,

[devongovett]

Good catch on JSX, and thanks for fixing @existentialism! 😍