Disallow side-by-side arguments in calls

[DavisVaughan]

Closes #140

Inspired by "array hole" support in tree-sitter-javascript, i.e. [1, , , 2]
https://github.com/tree-sitter/tree-sitter-javascript/blob/108b2d4d17a04356a340aea809e4dd5b801eb40d/grammar.js#L570-L577

The usage of delimSep1(optional(field("argument", $.argument)), $.comma) fully expands into what you see below. If you squint at it long enough you will see that it passes all of the required allowed vs not allowed examples there.

// # Allowed
// fn()
// fn(,)
// fn(,,)
// fn(a)
// fn(a, b)
// fn(,,a,,b,,)
// fn(a, # comment_between_commas
// ,)
//
// # Not allowed
// fn(a b)

seq(
  open,
  seq(
    optional(field("argument", $.argument)),
    repeat(
      seq(
        $.comma,
        optional(field("argument", $.argument))
      )
    )
  ),
  close
)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Please upload report for BASE (main@c094bd5). Learn more about missing BASE report.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #153   +/-   ##
=======================================
  Coverage        ?   82.40%           
=======================================
  Files           ?        7           
  Lines           ?      955           
  Branches        ?        0           
=======================================
  Hits            ?      787           
  Misses          ?      168           
  Partials        ?        0           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

---

🚨 Try these New Features:

• Flaky Tests Detection - Detect and resolve failed and flaky tests
• JS Bundle Analysis - Avoid shipping oversized bundles

[kevinushey]

Looks good to me! Some things worth verifying:

Do we still get the correct behavior when highlighting the current argument in the signature tooltip? Does this affect what label is highlighted in the presence of missing commas?

Similarly, will this affect how we read / infer the "nth" argument in a function call for diagnostics and other code analysis in ark?

[DavisVaughan]

@kevinushey good questions. IIUC this particular change has 0 effect on the ASTs we were generating on valid R code. i.e. the tree generated from fn(, , ,) before and after this commit is the same, because that is valid R code.

The change is that we now just catch fn(a + b c) as invalid R code in the tree-sitter parser.

Here is current arg signature behavior still working with this commit over in Positron: