nix: Add fenced language syntaxes

ftplugin/nix.vim

@@ -22,4 +22,117 @@ if get(g:, 'nix_recommended_style', 1)
     \ expandtab 
 endif
 
+" Borrowed from vim-markdown: https://github.com/plasticboy/vim-markdown/
+if exists('g:vim_nix_fenced_languages')
+  let s:filetype_dict = {}
+  for s:filetype in g:vim_nix_fenced_languages
+    let key = matchstr(s:filetype, "[^=]*")
+    let val = matchstr(s:filetype, "[^=]*$")
+    let s:filetype_dict[key] = val
+  endfor
+else
+  let s:filetype_dict = {
+    \ 'c++': 'cpp',
+    \ 'viml': 'vim',
+    \ 'bash': 'sh',
+    \ 'ini': 'dosini'
+  \ }
+endif
+
+function! s:NixHighlightSources(force)
+  " Syntax highlight source code embedded in notes.
+  " Look for code blocks in the current file
+  let filetypes = {}
+  for line in getline(1, '$')
+    let ft = matchstr(line, "/\\*\\s*\\zs[0-9A-Za-z_+-]*\\ze\\s*\\*/\\s*''")
+    if !empty(ft) && ft !~ '^\d*$' | let filetypes[ft] = 1 | endif
+  endfor
+  if !exists('b:nix_known_filetypes')
+    let b:nix_known_filetypes = {}
+  endif
+  if !exists('b:nix_included_filetypes')
+    " set syntax file name included
+    let b:nix_included_filetypes = {}
+  endif
+  if !a:force && (b:nix_known_filetypes == filetypes || empty(filetypes))
+    return
+  endif
+
+  " Now we're ready to actually highlight the code blocks.
+  for ft in keys(filetypes)
+    if a:force || !has_key(b:nix_known_filetypes, ft)
+      if has_key(s:filetype_dict, ft)
+        let filetype = s:filetype_dict[ft]
+      else
+        let filetype = ft
+      endif
+      let group = 'nixSnippet' . toupper(substitute(filetype, "[+-]", "_", "g"))
+      if !has_key(b:nix_included_filetypes, filetype)
+        let include = s:SyntaxInclude(filetype)
+        let b:nix_included_filetypes[filetype] = 1
+      else
+        let include = '@' . toupper(filetype)
+      endif
+      let command = "syn region %s matchgroup=nixCodeStart start=@/\\*\\s*%s\\s*\\*/\\s*''@ matchgroup=NONE skip=+''['$\\\\]+ matchgroup=nixCodeEnd end=+''+ keepend extend contains=nixInterpolation,nixStringSpecial,nixInvalidStringEscape,%s"
+      execute printf(command, group, ft, include)
+      execute printf("syn cluster nixExpr add=%s", group)
+      execute printf("syn region nixInterpolation matchgroup=nixInterpolationDelimiter start=+\\(''\\)\\@<!\\${+ end=+}+ containedin=%s contains=@nixExpr,nixInterpolationParam", include)
+      execute printf("syn match nixStringSpecial /''\\$/me=e-1 containedin=%s", include)
+      execute printf("syn match nixStringSpecial /'''/me=e-2 containedin=%s", include)
+      execute printf("syn match nixStringSpecial /''\\\\[nrt]/ containedin=%s", include)
+      execute printf("syn match nixInvalidStringEscape /''\\\\[^nrt]/ containedin=%s", include)
+
+      let b:nix_known_filetypes[ft] = 1
+    endif
+  endfor
+endfunction
+
+function! s:SyntaxInclude(filetype)
+  " Include the syntax highlighting of another {filetype}.
+  let grouplistname = '@' . toupper(a:filetype)
+  " Unset the name of the current syntax while including the other syntax
+  " because some syntax scripts do nothing when "b:current_syntax" is set
+  if exists('b:current_syntax')
+    let syntax_save = b:current_syntax
+    unlet b:current_syntax
+  endif
+  try
+    execute 'syntax include' grouplistname 'syntax/' . a:filetype . '.vim'
+    execute 'syntax include' grouplistname 'after/syntax/' . a:filetype . '.vim'
+  catch /E484/
+    " Ignore missing scripts
+  endtry
+  " Restore the name of the current syntax
+  if exists('syntax_save')
+    let b:current_syntax = syntax_save
+  elseif exists('b:current_syntax')
+    unlet b:current_syntax
+  endif
+  return grouplistname
+endfunction
+
+
+function! s:NixRefreshSyntax(force)
+  if &filetype =~ 'nix' && line('$') > 1
+    call s:NixHighlightSources(a:force)
+  endif
+endfunction
+
+function! s:NixClearSyntaxVariables()
+  if &filetype =~ 'nix'
+    unlet! b:nix_included_filetypes
+  endif
+endfunction
+
+augroup Nix
+  " These autocmd calling s:NixRefreshSyntax need to be kept in sync with
+  " the autocmds calling s:NixSetupFolding in after/ftplugin/markdown.vim.
+  autocmd! * <buffer>
+  autocmd BufWinEnter <buffer> call s:NixRefreshSyntax(1)
+  autocmd BufUnload <buffer> call s:NixClearSyntaxVariables()
+  autocmd BufWritePost <buffer> call s:NixRefreshSyntax(0)
+  autocmd InsertEnter,InsertLeave <buffer> call s:NixRefreshSyntax(0)
+  autocmd CursorHold,CursorHoldI <buffer> call s:NixRefreshSyntax(0)
+augroup END
+
 endif

syntax/nix.vim

@@ -46,6 +46,7 @@ syn match nixInvalidStringEscape /''\\[^nrt]/ contained
 
 syn region nixSimpleString matchgroup=nixStringDelimiter start=+"+ skip=+\\"+ end=+"+ contains=nixInterpolation,nixSimpleStringSpecial,nixInvalidSimpleStringEscape
 syn region nixString matchgroup=nixStringDelimiter start=+''+ skip=+''['$\\]+ end=+''+ contains=nixInterpolation,nixStringSpecial,nixInvalidStringEscape
+syn region nixFencedString matchgroup=nixCodeStart start=+/\*\s*[0-9A-Za-z_+-]*\s*\*/\s*''+ skip=+''['$\\]+ matchgroup=nixCodeEnd end=+''+ keepend extend contains=nixInterpolation,nixStringSpecial,nixInvalidStringEscape
 
 syn match nixFunctionCall "[a-zA-Z_][a-zA-Z0-9_'-]*"
 
@@ -161,6 +162,8 @@ hi def link nixAttribute                 Identifier
 hi def link nixAttributeDot              Operator
 hi def link nixBoolean                   Boolean
 hi def link nixBuiltin                   Special
+hi def link nixCodeEnd                   Delimiter
+hi def link nixCodeStart                 Delimiter
 hi def link nixComment                   Comment
 hi def link nixConditional               Conditional
 hi def link nixHomePath                  Include
@@ -185,6 +188,7 @@ hi def link nixSimpleFunctionArgument    Identifier
 hi def link nixSimpleString              String
 hi def link nixSimpleStringSpecial       SpecialChar
 hi def link nixString                    String
+hi def link nixFencedString              String
 hi def link nixStringDelimiter           Delimiter
 hi def link nixStringSpecial             Special
 hi def link nixTodo                      Todo