Colorize arrow function parameters without parens

[caleb531]

Requirements

• Filling out the template is required. Any pull request that does not include enough information to be reviewed in a timely manner may be closed at the maintainers' discretion.
• All new code requires tests to ensure against regressions

Description of the Change

This PR tokenizes single (paren-less) parameters for arrow functions. The first-mate source.js grammar already did this, while the current tree-sitter grammar does not. Consider the following screenshots:

Current tree-sitter grammar:

Tree-sitter grammar with this PR applied:

Current first-mate grammar:

Alternate Designs

A different selector could be used or the precedence of the grammar rule could be adjusted, if need be. Although this seems to work without any repercussions.

Benefits

More consistent coloring for arrow function parameters, whether or not you use parens.

Possible Drawbacks

I suppose if the selector chosen tokenizes more than it should, but I tried to keep it simple enough that it shouldn't be a concern.

Applicable Issues

N/A

[rsese]

Thanks again @caleb531, someone will take a look as soon as they can :v:

[rsese]

Failure looks unrelated, we restarted it but same error.

[jasonrudolph]

:wave: Hi @caleb531: Thanks for this! :bow: I tested this out locally, and I do see that this pull request causes the arrow function parameters to have a new scope, but I don't see any change to the syntax highlighting. It's possible that I'm doing something wrong, so I'll show you what I'm seeing, and you can let me know if I'm missing something. 😅

Note: All of the examples below are using Atom 1.42.0-nightly1 and the monokai syntax theme.

With Tree-Sitter parsers disabled

With Tree-Sitter parsers enabled

With Tree-Sitter parsers enabled using the changes from this pull request

---

I see that the formal-parameter scope gets applied, but I'm not sure if syntax themes are using that scope or not. Instead of applying the formal-parameter scope, should we instead apply the same scopes used in the TextMate grammar (i.e., meta-method-call meta.arguments meta.function.arrow meta.parameters variable.parameter.function)?

[caleb531]

@jasonrudolph Ha, that's because it turns out I have the following styles in my styles.less:

atom-text-editor:not([mini]) .syntax--source.syntax--js .syntax--formal-parameter.syntax--identifier {
   color: @orange;
}

My apologies about that. But I agree, variable.parameter.function would be the way to go (as this scope is already used in the Python tree-sitter grammar, and the color of those parameters is already orange for monokai, as it should be)

[jasonrudolph]

But I agree, variable.parameter.function would be the way to go...

@caleb531: Cool. Wanna make that change?

[caleb531]

@jasonrudolph Just pushed the rebased changes! The scope is now variable.parameter.function.

[jasonrudolph]

Just pushed the rebased changes!

Thanks, @caleb531! 🚀