Parsing error for generic function with index signature return type

[OliverJAsh]

What version of TypeScript are you using?
2.4.1

What version of typescript-eslint-parser are you using?
8

What code were you trying to parse?

const x = <T>(): { [x: string]: string } => ({});

What did you expect to happen?
No error

What happened?

[eslint] Parsing error: ',' expected.

[JamesHenry]

I believe this behaviour is correct.

The source you have provided is genuinely a parse error in TypeScript 2.4.x:

http://astexplorer.net/#/gist/69f89d5c7455a7713684a53d49bdf7b1/67a4d6d0992298f9840e1b8fefe601c101ae3e40

(See the parseDiagnostics array)

In 2.5.x it seems to produce a valid AST with this parser. Please feel free to reopen if you have any more information.

[OliverJAsh]

The example is valid in TypeScript 2.4 and 2.5 only for .ts extensions—not when JSX is enabled, e.g. .tsx). I believe astexplorer.net is enabling JSX.

You can try it here: https://github.com/OliverJAsh/typescript-eslint-parser-parse-error-test

Therefore I do believe the example above should not produce an ESLint parse error for non-JSX files, i.e. .ts.

[OliverJAsh]

Here is an example of the error occurring inside a non-JSX (.ts) file (updated):

[JamesHenry]

Ah yes you are right and this then is the same case as the one I dug into yesterday:

#392 (comment)

As outlined in that comment, you will need to disable jsx in your ESLint config or use constructs which are not ambiguous for TypeScript when in "JSX mode".

I have opened an issue to see if we can make the setting inferrable from file extension in the long run: #399

[OliverJAsh]

Thank you, that makes sense!