New lint to not use {} in generic

[donyunardi]

Based on Hadley's suggestion:
https://github.com/hadley/adv-r/blob/dc49c3872c3530ac08716fd4f4c235b01266a4ce/S4.Rmd#L345-L352

It is bad practice to use {} in the generic as it triggers a special case that is more expensive, and generally best avoided.

# Don't do this!
 setGeneric("myGeneric", function(x) {
 standardGeneric("myGeneric")
})

Would it be a good idea to create a lint for this rule?

Linking with:
insightsengineering/teal.code#109

[MichaelChirico]

SGTM. It will be part of brace_linter(). Note that there are two things:

• Throw a lint if { is used in the def= (2nd positional) argument of setGeneric, either \(...) { ... } or function(...) { ... }
• Don't throw a lint if { is excluded from a multi-line function in the def= argument of setGeneric

The latter can come up for long definitions like

setGeneric(
  "myLongGeneric",
  function(a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p)
    standardGeneric("myLongGeneric")
)

where bumping the line is used to avoid line_length_linter() hits.

[MichaelChirico]

Hmm actually in the multi-line case, {styler} will auto-include the { as well. So might need a companion issue, WDYT @lorenzwalthert?

cc also @IndrajeetPatil as our designated liaison :)

[MichaelChirico]

Linking {styler} tracker: r-lib/styler#1141