Add "ac" ("a comment") text object

[arp242]

To select a comment block. Fixes #1508

Requires fatih/motion#4

[fatih]

Is there way we could support ic as well? This could be handy if we want to remove the comment with leaving it intact. For example // this is a comment could be deleted via dic, so it would end up with //

[arp242]

Yes, that would be useful, it is a little bit tricky to get it to behave intuitively in cases with multi-line comments, but I think I got it right.

[fatih]

Just tried it out and seems like ic is not working then it's intended (groups of const, vars, imports, etc..). For example:

// Options is used to setup Kubernetes
type Options struct {
	// Client is the underlying client manager uses for core resources
	Client kubernetes.Interface
}

ic works for the first comment above, not for the second one. It deletes the whole line when you type dic

[fatih]

The following fixes it:

$ vim-go git:(Carpetsmoker-ac) ✗ git diff
diff --git a/autoload/go/textobj.vim b/autoload/go/textobj.vim
index 2f60046..164b769 100644
--- a/autoload/go/textobj.vim
+++ b/autoload/go/textobj.vim
@@ -44,7 +44,9 @@ function! go#textobj#Comment(mode) abort
   " Adjust cursor to exclude start comment markers. Try to be a little bit
   " clever when using multi-line '/*' markers.
   if a:mode is# 'i'
-    let l:line = getline('.')
+    " trim whitespace so matching below works correctly
+    let l:line = substitute(getline('.'), '^\s*\(.\{-}\)\s*$', '\1', '')
+
     " //text
     if l:line[:2] is# '// '
       call cursor(l:info.startLine, l:info.startCol+3)

I'll merge this PR and apply the fix above.