detect missing() usage in function_argument_linter

[MichaelChirico]

Closes #1546

[codecov-commenter]

Codecov Report

Merging #2095 (0de3eac) into main (cafc081) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 0de3eac differs from pull request most recent head d6b8372. Consider uploading reports for the commit d6b8372 to get more accurate results

@@           Coverage Diff           @@
##             main    #2095   +/-   ##
=======================================
  Coverage   99.65%   99.65%           
=======================================
  Files         118      118           
  Lines        5201     5206    +5     
=======================================
+ Hits         5183     5188    +5     
  Misses         18       18           

Files Changed	Coverage Δ
R/function_argument_linter.R	100.00% <100.00%> (ø)

[AshesITR]

Can we add a test case without {} in the function body?

function(x = 2, y) if (missing(y)) x else y

Just to make sure the XPath works everywhere.
The rest looks good.

[AshesITR]

Wait now this has no diff to main wrt NEWS.md 😅

[MichaelChirico]

Oh, whoops. Should open my eyes wider. I mis-read and thought it was the fixed_regex_linter() bullet back again. Restored.