Add option to disable signature help syntax highlights

Author: puremourning

README.md

@@ -889,7 +889,8 @@ Signature help is triggered in insert mode automatically when
 `g:ycm_auto_trigger` is enabled and is not supported when it is not enabled.
 
 The signatures popup is hidden when there are no matching signatures or when you
-leave insert mode. There is no key binding to clear the popup.
+leave insert mode. If you want to manually control when it is visible, you can
+map something to `<plug>YCMToggleSignatureHelp` (see below).
 
 For more details on this feature and a few demos, check out the
 [PR that proposed it][signature-help-pr].
@@ -3689,6 +3690,19 @@ Default: `0`
 let g:ycm_disable_signature_help = 1
 ```
 
+### The `g:ycm_signature_help_disable_syntax` option
+
+Set this to 1 to disable syntax highlighting in the signature help popup. Thiis
+can help if your colourscheme doesn't work well with the default highliting and
+inverse video.
+
+Default: `0`
+
+```viml
+" Disable signature help syntax highliting
+let g:ycm_signature_help_disable_syntax = 1
+```
+
 ### The `g:ycm_gopls_binary_path` option
 
 In case the system-wide `gopls` binary is newer than the bundled one, setting

python/ycm/signature_help.py

@@ -189,7 +189,11 @@ def UpdateSignatureHelp( state, signature_info ): # noqa
   if state.state == SignatureHelpState.ACTIVE:
     vim.eval( f'popup_show( { state.popup_win_id } )' )
 
-  syntax = utils.ToUnicode( vim.current.buffer.options[ 'syntax' ] )
+  if vim.vars.get( 'ycm_signature_help_disable_syntax', False ):
+    syntax = ''
+  else:
+    syntax = utils.ToUnicode( vim.current.buffer.options[ 'syntax' ] )
+
   active_signature = int( signature_info.get( 'activeSignature', 0 ) )
   vim.eval( f"win_execute( { state.popup_win_id }, "
             f"'set syntax={ syntax } cursorline | "