feat: annotated code blocks

[clason]

This is a Lua block: >lua
    local foo = 'bar'

This is a Vimscript block: >vim
    au FileType lua setl sw=2

This is a C block: >c
    int *p = get_local_errno(); *p = EINVAL
<
This is a standard block: >
    $ nvim --clean +'q'
<

Note that the alternative syntax lua> is much trickier, since the rule for the language marker lua conflicts with normal text rule for the word lua. In either case, the added markers are trivial (and necessary) to add to the legacy syntax file.

Closes #2

[clason]

@justinmk I think this is good to go. The next step is to adapt scripts/gen_help_html.lua to

1. eat the language node
2. only show the code node wrapped in a <code class='language-<language>'></code> block

and inject highlight.js to the neovim.io/doc/user pages. But for that the ball is in your corner :)

[justinmk]

I found some cases in the help docs that we should test for:

runtime/bugreport.vim|20 col 20| :  !echo "uname -a" >bugreport.txt
runtime/doc/eval.txt|1051 col 2| >0 / 0  =  0x7fffffff  (like positive infinity)
runtime/doc/eval.txt|1057 col 2| >0 / 0  =  0x7fffffffffffffff  (like positive infinity)
runtime/doc/luaref.txt|460 col 24| while (  step  >0 and  var  <=  limit  )
runtime/doc/usr_02.txt|548 col 7| :help >cont
runtime/doc/usr_10.txt|707 col 17| sort <input.txt >output.txt

[clason]

runtime/bugreport.vim|20 col 20| : !echo "uname -a" >bugreport.txt

Not a help file.

runtime/doc/eval.txt|1051 col 2| >0 / 0 = 0x7fffffff (like positive infinity) runtime/doc/eval.txt|1057 col 2| >0 / 0 = 0x7fffffffffffffff (like positive infinity)

Not at the end of the line, so doesn't match.

runtime/doc/luaref.txt|460 col 24| while ( step >0 and var <= limit ) runtime/doc/usr_02.txt|548 col 7| :help >cont runtime/doc/usr_10.txt|707 col 17| sort output.txt

Inside a codeblock (and not on the end of the line or not [a-z0-9]+), so doesn't match.

[justinmk]

Not at the end of the line, so doesn't match.

worth adding an explicit case to the corpus?

[clason]

Oh, I see what you mean. Yes, I can see about adding a case with whitespace and not at the end of the line; maybe variants of the usr_*.txt examples.

[justinmk]

not a blocker, but this bugs me about >lua :

• more likely to have false positives than lua>
• lua> is more visually noticeable (for non-concealed text) because > is at EOL as usual

This is just thinking out loud. Will merge this later this week.

[clason]

Sorry, I tried to make that work; I failed.