Is special support for line directives needed?

[EagleoutIce]

Similar to #68, highlighting line directives such as #line 42 example.R instead of parsing them simply as (program (comment)) could be beneficial.
The default R parser handles it as a separate LINE_DIRECTIVE token:

> getParseData(parse(text="#line 42 example.R"))
  line1 col1 line2 col2 id parent          token terminal               text
1     1    1     1   18  1      0 LINE_DIRECTIVE     TRUE #line 42 example.R

[DavisVaughan]

Mayyyyybe. They aren't used that frequently from what I've seen.

We would probably want to nest them within comment somehow if we did this, like (program (comment (line_directive <fields>))) so that people can iterate over comments and have line directives be included by default, which seems like what you'd want. And you can just skip them (by recognizing the node kind of the child) if you care about handling them separately.

I'm more convinced about including this than roxygen2 support, since this is literally built into the language, but I'm not sure the very small benefit is worth the effort / headache.

You could also use a query to locate them today, but you'd have to do some additional work to make sure they are at the 1st column of the line, and match the correct form of a line directive

query <- '
(
  (comment) @comment
  (#match? @comment "^#line")
)
'

language <- treesitter.r::language()
query <- treesitter::query(language, query)

text <- "
1 + 1
# comment
#line 43 example.R
2 + 2
# comment2
#line 45 example2.R
"

node <- treesitter::text_parse(text, language)

captures <- treesitter::query_captures(query, node)

captures$node
#> [[1]]
#> <tree_sitter_node>
#> 
#> ── Text ────────────────────────────────────────────────────────────────────────
#> #line 43 example.R
#> 
#> ── S-Expression ────────────────────────────────────────────────────────────────
#> (comment [(3, 0), (3, 18)])
#> 
#> [[2]]
#> <tree_sitter_node>
#> 
#> ── Text ────────────────────────────────────────────────────────────────────────
#> #line 45 example2.R
#> 
#> ── S-Expression ────────────────────────────────────────────────────────────────
#> (comment [(6, 0), (6, 19)])

---

https://github.com/wch/r-source/blob/0a55f06ce3b46c4fd8d3c85b50c4ccb94d7653ef/src/main/gram.y#L2528-L2546
https://github.com/wch/r-source/blob/0a55f06ce3b46c4fd8d3c85b50c4ccb94d7653ef/src/main/gram.y#L3467-L3487

A few notes

• It has to start at column 0 in the row (which may be hard with tree-sitter, although the external scanner does have get_column() but its not free)
• It leads with #line and has to have a digit, but seems like the file name is optional
• The file name could be quoted in "