Dynamically set comments setting

I had a problem where Vim doesn't automatically insert the comment
character to the start of the line when I press <CR> in a comment in Vue
files even if I have the `r` option in my `formatoptions`.

The problem turned out to be because Vue files have the `comments`
setting set to `s:<!--,m:    ,e:-->` which is valid for HTML, but not
for the sections that include other languages. The `comments` setting
should be modified automatically in the exact same way that
`commentstring` is currently. So, I thought that it might make sense to
add this functionality to this plugin.

Author: JoosepAlviste

autoload/context/commentstring.vim

@@ -47,3 +47,9 @@ let g:context#commentstring#table.vue = {
 			\ 'cssStyle'    : '/*%s*/',
 			\}
 
+let g:context#commentstring#comments_table = {}
+let g:context#commentstring#comments_table.vue = {
+			\ 'htmlTag': 's:<!--,m:    ,e:-->',
+			\ 'vue_typescript': 's1:/*,mb:*,ex:*/,://',
+			\ 'cssStyle': 's1:/*,mb:*,ex:*/,://',
+			\ }

doc/context-commentstring.txt

@@ -55,6 +55,11 @@ Pope's |commentary.txt| plugin, a utility to comment and uncomment lines of
 code. Find the plugin at:
 	https://github.com/tpope/vim-commentary
 
+Additionally, this plugin sets the value of the 'comments' setting
+automatically. The 'comments' setting describes how inserting new lines should
+be handled when inside a comment region. This automatic formatting can be
+configured via the 'formatoptions' setting.
+
 ------------------------------------------------------------------------------
 INSTALLATION				*context-commentstring-installation*
 
@@ -112,6 +117,10 @@ syntax groups. When you are done with your testing, remove the echo doing: >
 	augroup END
 <
 
+The 'comments' setting can be configured the exact same way as 'commentstring'
+but the variable to change is >
+	g:context#commentstring#comments_table
+
 
 ==============================================================================
 BUGS					*context-commentstring-bugs*

plugin/context-commentstring.vim

@@ -22,6 +22,10 @@ function! s:Setup()
 			let b:original_commentstring=&l:commentstring
 			autocmd CursorMoved <buffer> call <SID>UpdateCommentString()
 		endif
+		if !empty(&filetype) && has_key(g:context#commentstring#comments_table, &filetype)
+			let b:original_comments=&l:comments
+			autocmd CursorMoved <buffer> call <SID>UpdateComments()
+		endif
 	augroup END
 endfunction
 
@@ -40,4 +44,19 @@ function! s:UpdateCommentString()
 endfunction
 
 
+function! s:UpdateComments()
+	let stack = synstack(line('.'), col('.'))
+	call reverse(stack)
+	if !empty(stack)
+		for name in map(stack, 'synIDattr(v:val, "name")')
+			if has_key(g:context#commentstring#comments_table[&filetype], name)
+				let &l:comments = g:context#commentstring#comments_table[&filetype][name]
+				return
+			endif
+		endfor
+	endif
+	let &l:commentstring = b:original_comments
+endfunction
+
+
 let g:loaded_context_commentstring = 1