Health: introduce help links (#5557)

We can now use help links like in normal help pages. The bars around them will
be concealed as well.

* Health: link string "SUCCESS" to ModeMsg

So far we linked "SUCCESS" to the Function highlight group.

The newly introduced healthHelp group links to Idenfifier as it does for links
in normal help pages.

Now the problem is that the Function group links again to Identifier as well, so
both, "SUCCESS" and help links, would use the same colors.

* Health: don't use Markdown code blocks

Every line indented by more than 4 spaces would lose its highlighting otherwise.

* Health: add helper health#help_to_link()

runtime/autoload/health.vim

@@ -9,13 +9,20 @@ function! s:enhance_syntax() abort
   highlight link healthInfo ModeMsg
 
   syntax keyword healthSuccess SUCCESS
-  highlight link healthSuccess Function
+  highlight link healthSuccess ModeMsg
 
   syntax keyword healthSuggestion SUGGESTIONS
   highlight link healthSuggestion String
 
+  syntax match healthHelp "|.\{-}|" contains=healthBar
+  syntax match healthBar  "|" contained conceal
+  highlight link healthHelp Identifier
+
   " We do not care about markdown syntax errors in :CheckHealth output.
   highlight! link markdownError Normal
+
+  " We don't need code blocks.
+  syntax clear markdownCodeBlock
 endfunction
 
 " Runs the specified healthchecks.
@@ -28,6 +35,8 @@ function! health#check(plugin_names) abort
   tabnew
   setlocal wrap breakindent
   setlocal filetype=markdown bufhidden=wipe
+  setlocal conceallevel=2 concealcursor=nc
+  setlocal keywordprg=:help
   call s:enhance_syntax()
 
   if empty(healthchecks)
@@ -78,6 +87,11 @@ function! s:indent_after_line1(s, columns) abort
   return join(lines, "\n")
 endfunction
 
+" Changes ':help clipboard' to '|clipoard|'. Also removes surrounding quotes.
+function! s:help_to_link(s) abort
+  return substitute(a:s, '\v[''"]?:h%[elp] ([^''"]+)[''"]?', '|\1|', 'g')
+endfunction
+
 " Format a message for a specific report item
 function! s:format_report_message(status, msg, ...) abort " {{{
   let output = '  - ' . a:status . ': ' . s:indent_after_line1(a:msg, 4)
@@ -99,7 +113,7 @@ function! s:format_report_message(status, msg, ...) abort " {{{
     let output .= "\n      - " . s:indent_after_line1(suggestion, 10)
   endfor
 
-  return output
+  return s:help_to_link(output)
 endfunction " }}}
 
 " Use {msg} to report information in the current section

runtime/autoload/health/provider.vim

@@ -53,7 +53,7 @@ function! s:check_clipboard() abort
   if empty(clipboard_tool)
     call health#report_warn(
           \ "No clipboard tool found. Using the system clipboard won't work.",
-          \ ['See ":help clipboard"'])
+          \ ['See |clipboard|.'])
   else
     call health#report_ok('Clipboard tool found: '. clipboard_tool)
   endif