Support using vim-gnupg from cygwin with Gpg4win

Gpg4win expects native Windows paths even when it's being run from a
cygwin environment.  In order to satisfy that, update `s:shellescape` to
know whether it should convert the paths to native Windows paths using
`cygpath -am`.

In order to detect whether cygpath should be invoked, look for the
combination of `has('win32unix')` being true and `gpg --version`
reporting a Windows style path for gpg's home directory.

Closes jamessan/vim-gnupg#62

Signed-off-by: James McCoy <jamessan@jamessan.com>

plugin/gnupg.vim

@@ -220,24 +220,35 @@ highlight default link GPGHighlightUnknownRecipient ErrorMsg
 
 " Section: Functions {{{1
 
-" Function: s:shellescape(s[, special]) {{{2
+" Function: s:shellescape(s[, dict]) {{{2
 "
 " Calls shellescape(), also taking into account 'shellslash'
 " when on Windows and using $COMSPEC as the shell.
 "
+" Recognized keys are:
+" special - Passed through as special argument for Vim's shellescape()
+" cygpath - When true and s:useCygpath is true, adjust the path to work with
+"           Gpg4win from cygwin
+"
 " Returns: shellescaped string
 "
 function s:shellescape(s, ...)
-  let special = a:0 ? a:1 : 0
+  let opts = a:0 ? a:1 : {}
+  let special = get(opts, 'special', 0)
+  let cygpath = get(opts, 'cygpath', 0)
+  let s = a:s
+  if cygpath && s:useCygpath
+    let s = matchstr(system('cygpath -am '.shellescape(s)), '[^\x0a\x0d]*')
+  endif
   if exists('+shellslash') && &shell == $COMSPEC
     let ssl = &shellslash
     set noshellslash
 
-    let escaped = shellescape(a:s, special)
+    let escaped = shellescape(s, special)
 
     let &shellslash = ssl
   else
-    let escaped = shellescape(a:s, special)
+    let escaped = shellescape(s, special)
   endif
 
   return escaped
@@ -387,6 +398,13 @@ function s:GPGInit(bufread)
   let s:GPGCipher = substitute(output, ".*Cipher: \\(.\\{-}\\)\n.*", "\\1", "")
   let s:GPGHash = substitute(output, ".*Hash: \\(.\\{-}\\)\n.*", "\\1", "")
   let s:GPGCompress = substitute(output, ".*Compress.\\{-}: \\(.\\{-}\\)\n.*", "\\1", "")
+  let s:GPGHome = matchstr(output, '.*Home: \zs.\{-}\ze\r\=\n')
+
+  let s:useCygpath = 0
+  if has('win32unix') && s:GPGHome =~ '\a:[/\\]'
+    call s:GPGDebug(1, 'Enabling use of cygpath')
+    let s:useCygpath = 1
+  endif
 
   " determine if gnupg can use the gpg-agent
   if (str2float(gpgversion) >= 2.1 || (exists("$GPG_AGENT_INFO") && g:GPGUseAgent == 1))
@@ -476,7 +494,7 @@ function s:GPGDecrypt(bufread)
 
   " find the recipients of the file
   let cmd = { 'level': 3 }
-  let cmd.args = '--verbose --decrypt --list-only --dry-run --no-use-agent --logger-fd 1 ' . s:shellescape(filename)
+  let cmd.args = '--verbose --decrypt --list-only --dry-run --no-use-agent --logger-fd 1 ' . s:shellescape(filename, { 'cygpath': 1 })
   let output = s:GPGSystem(cmd)
 
   " Suppress the "N more lines" message when editing a file, not when reading
@@ -568,7 +586,7 @@ function s:GPGDecrypt(bufread)
     " we must redirect stderr (using shell temporarily)
     call s:GPGDebug(1, "decrypting file")
     let cmd = { 'level': 1, 'ex': silent . 'read ++edit !' }
-    let cmd.args = '--quiet --decrypt ' . s:shellescape(filename, 1)
+    let cmd.args = '--quiet --decrypt ' . s:shellescape(filename, { 'special': 1, 'cygpath': 1 })
     call s:GPGExecute(cmd)
 
     if (v:shell_error) " message could not be decrypted
@@ -710,7 +728,7 @@ function s:GPGEncrypt()
   let destfile = tempname()
   let cmd = { 'level': 1, 'ex': "'[,']write !" }
   let cmd.args = '--quiet --no-encrypt-to ' . options
-  let cmd.redirect = '>' . s:shellescape(destfile, 1)
+  let cmd.redirect = '>' . s:shellescape(destfile, { 'special': 1, 'cygpath': 1 })
   silent call s:GPGExecute(cmd)
 
   if (v:shell_error) " message could not be encrypted
@@ -1349,7 +1367,7 @@ endfunction
 function s:GPGSystem(dict)
   let commandline = s:GPGCommand
   if (!empty(g:GPGHomedir))
-    let commandline .= ' --homedir ' . s:shellescape(g:GPGHomedir)
+    let commandline .= ' --homedir ' . s:shellescape(g:GPGHomedir, { 'cygpath': 1 })
   endif
   let commandline .= ' ' . a:dict.args
   let commandline .= ' ' . s:stderrredirnull
@@ -1376,7 +1394,7 @@ endfunction
 function s:GPGExecute(dict)
   let commandline = printf('%s%s', a:dict.ex, s:GPGCommand)
   if (!empty(g:GPGHomedir))
-    let commandline .= ' --homedir ' . s:shellescape(g:GPGHomedir, 1)
+    let commandline .= ' --homedir ' . s:shellescape(g:GPGHomedir, { 'special': 1, 'cygpath': 1 })
   endif
   let commandline .= ' ' . a:dict.args
   if (has_key(a:dict, 'redirect'))