Set up basic highlighting for snipmate files

Try to detect a snipmate-formatted file by looking at the directory name
and searching for endsnippet. If we think it's a snipmate file, switch
over to an alternative syntax highlighting variant.

syntax/snippets.vim

@@ -5,6 +5,15 @@ if exists("b:current_syntax")
   finish
 endif
 
+if expand("%:p:h:t") == "snippets" && search("^endsnippet", "nw") == 0
+            \ && !exists("b:ultisnips_override_snipmate")
+    " this appears to be a snipmate file
+    " It's in a directory called snippets/ and there's no endsnippet keyword
+    " anywhere in the file.
+    source <sfile>:h/snippets_snipmate.vim
+    finish
+endif
+
 " Embedded Syntaxes {{{1
 
 syntax include @Python syntax/python.vim
@@ -69,11 +78,12 @@ syn match snipSnippetOptionFlag ,[biwrts], contained
 
 " Command substitution {{{4
 
-syn region snipCommand keepend matchgroup=snipCommandDelim start="`" skip="\\[{}\\$`]" end="`" contains=snipPythonCommand,snipVimLCommand,snipShellCommand,snipCommandSyntaxOverride
+syn region snipCommand keepend matchgroup=snipCommandDelim start="`" skip="\\[{}\\$`]" end="`" contained contains=snipPythonCommand,snipVimLCommand,snipShellCommand,snipCommandSyntaxOverride
 syn region snipShellCommand start="\ze\_." skip="\\[{}\\$`]" end="\ze`" contained contains=@Shell
 syn region snipPythonCommand matchgroup=snipPythonCommandP start="`\@<=!p\_s" skip="\\[{}\\$`]" end="\ze`" contained contains=@Python
 syn region snipVimLCommand matchgroup=snipVimLCommandV start="`\@<=!v\_s" skip="\\[{}\\$`]" end="\ze`" contained contains=@Viml
 syn cluster snipTokens add=snipCommand
+syn cluster snipTabStopTokens add=snipCommand
 
 " unfortunately due to the balanced braces parsing of commands, if a { occurs
 " in the command, we need to prevent the embedded syntax highlighting.
@@ -85,19 +95,23 @@ syn region snipCommandSyntaxOverride start="\%(\\[{}\\$`]\|\_[^`"{]\)*\ze{" skip
 
 syn match snipEscape "\\[{}\\$`]" contained
 syn cluster snipTokens add=snipEscape
+syn cluster snipTabStopTokens add=snipEscape
 
 syn match snipMirror "\$\d\+" contained
 syn cluster snipTokens add=snipMirror
+syn cluster snipTabStopTokens add=snipMirror
 
 syn region snipTabStop matchgroup=snipTabStop start="\${\d\+[:}]\@=" end="}" contained contains=snipTabStopDefault
-syn region snipTabStopDefault matchgroup=snipTabStop start=":" skip="\\[{}]" end="\ze}" contained contains=snipTabStopEscape,snipBalancedBraces,@snipTokens keepend
+syn region snipTabStopDefault matchgroup=snipTabStop start=":" skip="\\[{}]" end="\ze}" contained contains=snipTabStopEscape,snipBalancedBraces,@snipTabStopTokens keepend
 syn match snipTabStopEscape "\\[{}]" contained
 syn region snipBalancedBraces start="{" end="}" contained transparent extend
 syn cluster snipTokens add=snipTabStop
+syn cluster snipTabStopTokens add=snipTabStop
 
 syn region snipVisual matchgroup=snipVisual start="\${VISUAL[:}/]\@=" end="}" contained contains=snipVisualDefault,snipTransformationPattern
 syn region snipVisualDefault matchgroup=snipVisual start=":" end="\ze[}/]" contained contains=snipTabStopEscape nextgroup=snipTransformationPattern
 syn cluster snipTokens add=snipVisual
+syn cluster snipTabStopTokens add=snipVisual
 
 syn region snipTransformation matchgroup=snipTransformation start="\${\d\/\@=" end="}" contained contains=snipTransformationPattern
 syn region snipTransformationPattern matchgroup=snipTransformationPatternDelim start="/" end="\ze/" contained contains=snipTransformationEscape nextgroup=snipTransformationReplace skipnl
@@ -105,6 +119,7 @@ syn region snipTransformationReplace matchgroup=snipTransformationPatternDelim s
 syn region snipTransformationOptions start="\ze[^}]" end="\ze}" contained contains=snipTabStopEscape
 syn match snipTransformationEscape "\\/" contained
 syn cluster snipTokens add=snipTransformation
+syn cluster snipTabStopTokens add=snipTransformation
 
 " global {{{3
 

syntax/snippets_snipmate.vim

@@ -0,0 +1,47 @@
+" Syntax highlighting variant used for snipmate snippets files
+" The snippets.vim file sources this if it wants snipmate mode
+
+if exists("b:current_syntax")
+    finish
+endif
+
+" Embedded syntaxes {{{1
+
+" Re-include the original file so we can share some of its definitions
+let b:ultisnips_override_snipmate = 1
+syn include <sfile>:h/snippets.vim
+unlet b:current_syntax
+unlet b:ultisnips_override_snipmate
+
+syn cluster snipTokens contains=snipEscape,snipVisual,snipTabStop,snipMirror,snipmateCommand
+syn cluster snipTabStopTokens contains=snipVisual,snipMirror,snipEscape,snipmateCommand
+
+" Syntax definitions {{{1
+
+syn match snipmateComment "^#.*"
+
+syn match snipmateExtends "^extends\%(\s.*\|$\)" contains=snipExtendsKeyword display
+
+syn region snipmateSnippet start="^snippet\ze\%(\s\|$\)" end="^\ze[^[:tab:]]" contains=snipmateSnippetHeader keepend
+syn match snipmateSnippetHeader "^.*" contained contains=snipmateKeyword nextgroup=snipmateSnippetBody skipnl skipempty
+syn match snipmateKeyword "^snippet\ze\%(\s\|$\)" contained nextgroup=snipmateTrigger skipwhite
+syn match snipmateTrigger "\S\+" contained nextgroup=snipmateDescription skipwhite
+syn match snipmateDescription "\S.*" contained
+syn region snipmateSnippetBody start="^\t" end="^\ze[^[:tab:]]" contained contains=@snipTokens
+
+syn region snipmateCommand keepend matchgroup=snipCommandDelim start="`" skip="\\[{}\\$`]" end="`" contained contains=snipCommandSyntaxOverride,@Viml
+
+" Highlight groups {{{1
+
+hi def link snipmateComment snipComment
+
+hi def link snipmateSnippet snipSnippet
+hi def link snipmateKeyword snipKeyword
+hi def link snipmateTrigger snipSnippetTrigger
+hi def link snipmateDescription snipSnippetDocString
+
+hi def link snipmateCommand snipCommand
+
+" }}}1
+
+let b:current_syntax = "snippets"