provider/clipboard.vim: allow configuration #6030

Closes #6029

runtime/autoload/provider/clipboard.vim

@@ -47,7 +47,12 @@ function! provider#clipboard#Error() abort
 endfunction
 
 function! provider#clipboard#Executable() abort
-  if has('mac') && executable('pbcopy')
+  if exists('g:clipboard')
+    let s:copy = g:clipboard.copy
+    let s:paste = g:clipboard.paste
+    let s:cache_enabled = g:clipboard.cache_enabled
+    return g:clipboard.name
+  elseif has('mac') && executable('pbcopy')
     let s:copy['+'] = 'pbcopy'
     let s:paste['+'] = 'pbpaste'
     let s:copy['*'] = s:copy['+']

runtime/doc/provider.txt

@@ -129,6 +129,25 @@ are found in your `$PATH`.
   - lemonade (for SSH) https://github.com/pocke/lemonade
   - doitclient (for SSH) http://www.chiark.greenend.org.uk/~sgtatham/doit/
 
+If you would like to configure the provider: >
+    let g:clipboard = {
+          \   'name': 'myClipboard',
+          \   'copy': {
+          \      '+': 'copyCommand',
+          \      '*': 'copyCommand',
+          \    },
+          \   'paste': {
+          \      '+': 'pasteCommand',
+          \      '*': 'pasteCommand',
+          \   },
+          \   'cache_enabled': 1,
+          \ }
+
+If the cache is enabled, then when a selection is copied and the copy command
+is executed, neovim will cache this selection until the copy command process
+dies. Then, when pasting, if the copy command process has not died, the cached
+selection is returned instead of executing the paste command.
+
 The presence of a suitable clipboard tool implicitly enables the '+' and '*'
 registers.