Breaking: switch 'jsx' option by filename (fixes #517)

[mysticatea]

This PR makes the parser setting jsx option by filename automatically.

• *.ts ... it sets jsx: false.
• *.tsx ... it sets jsx: true.
• Otherwise (E.g., *.js, not provided, etc...) ... respects the given jsx option.

(Edited at 2018-11-08 20:52Z)

Fixes #517.

[kaicataldo]

Thanks for working on this! I have a few questions/concerns.

[kaicataldo]

LGTM, thanks!

[JamesHenry]

You don't need to let this block the PR, but my two cents would be that this option has outgrown its boolean type.

It would be far clearer to have an enum of possible strings:

jsx: 'disabled' | 'enabled' | 'auto'

Or something like that, where 'auto' or 'infer' or similar is the option that looks at your file extension. You could also provide fallback of false being the same as 'disabled' and true being the same as 'enabled' so as not to break anyone.

[mysticatea]

@JamesHenry Thank you for the review.

The intention of this PR's spec is:

• It's always "auto" essentially because we cannot configure it on tsc -- we cannot use JSX syntax on *.ts files and cannot disable JSX syntax on *.tsx files on tsc. So the jsx option on TypeScript files doesn't make sense.
• But people may use this parser on other files such as *.js. Or if people use stdin, the filename is unknown. This jsx option is provided for such a case.
  E.g., curl a_url | eslint --stdin --perser-options jsx:true

[JamesHenry]

Ah I see, I get it now, thanks!

[kaicataldo]

Thanks for contributing!