How to test if certain event is supported?

Question

I want to test in a script if this version of vim supports the "CmdlineEnter" event.

This is a relatively new addition in vim and neovim doesn't support it in it's current 0.2.2 version (although there is a merged PR that adds that event)

How can I test if this event is supported in the current version of vim?

  has(CmdlineEnter)

raises an error.

Answer 1

There are at least three ways to tell if a particular autocmd is supported:

1. Use exists('##CmdlineEnter'). This should be exactly what you need.

2. Check for the patch it was introduced in. For example, CmdlineEnter was added in patch 8.0.1206. I determined this by looking at recent vim commits and git blame on the help files. Thus you can use has('patch-8.0.1206'). Although Neovim does not follow vim development exactly, when features are added from "upstream," the vim patch numbers are included too.

3. Use a try|catch|endtry block around autocmd. E.g.,

try
     silent autocmd CmdlineEnter
catch /^Vim\%((\a\+)\)\=:E216/
     " autocmd is not supported
endtry

When installing an autocmd handler you could simply use silent! autocmd CmdlineEnter * ... to suppress all errors, if your code doesn't actually need to know whether the command is supported.

Alternatively, you can check if an autocmd is subscribed to using exists('#CmdlineEnter'). This will return 0 if the autocmd exists but has no listeners. Sometimes this is all the info you need.