clipboard: macOS: fallback to tmux if pbcopy is broken #7940

On some versions of macOS, pbcopy doesn't work in tmux <2.6
https://superuser.com/q/231130
Fallback to tmux in that case.

Add a healthcheck for this scenario.

runtime/autoload/health/provider.vim

@@ -13,6 +13,12 @@ function! s:normalize_path(s) abort
   return substitute(substitute(a:s, '\', '/', 'g'), '/\./\|/\+', '/', 'g')
 endfunction
 
+" Returns TRUE if `cmd` exits with success, else FALSE.
+function! s:cmd_ok(cmd) abort
+  call system(a:cmd)
+  return v:shell_error == 0
+endfunction
+
 " Simple version comparison.
 function! s:version_cmp(a, b) abort
   let a = split(a:a, '\.', 0)
@@ -120,6 +126,13 @@ endfunction
 function! s:check_clipboard() abort
   call health#report_start('Clipboard (optional)')
 
+  if !empty($TMUX) && executable('tmux') && executable('pbcopy') && !s:cmd_ok('pbcopy')
+    let tmux_version = matchstr(system('tmux -V'), '\d\+\.\d\+')
+    call health#report_error('pbcopy does not work with tmux version: '.tmux_version,
+          \ ['Install tmux 2.6+.  https://superuser.com/q/231130',
+          \  'or use tmux with reattach-to-user-namespace.  https://superuser.com/a/413233'])
+  endif
+
   let clipboard_tool = provider#clipboard#Executable()
   if exists('g:clipboard') && empty(clipboard_tool)
     call health#report_error(

runtime/autoload/provider/clipboard.vim

@@ -26,7 +26,7 @@ let s:selections = { '*': s:selection, '+': copy(s:selection) }
 
 function! s:try_cmd(cmd, ...) abort
   let argv = split(a:cmd, " ")
-  let out = a:0 ? systemlist(argv, a:1, 1) : systemlist(argv, [''], 1)
+  let out = systemlist(argv, (a:0 ? a:1 : ['']), 1)
   if v:shell_error
     if !exists('s:did_error_try_cmd')
       echohl WarningMsg
@@ -64,7 +64,7 @@ function! provider#clipboard#Executable() abort
     let s:paste = get(g:clipboard, 'paste', { '+': v:null, '*': v:null })
     let s:cache_enabled = get(g:clipboard, 'cache_enabled', 0)
     return get(g:clipboard, 'name', 'g:clipboard')
-  elseif has('mac') && executable('pbcopy')
+  elseif has('mac') && executable('pbcopy') && s:cmd_ok('pbcopy')
     let s:copy['+'] = 'pbcopy'
     let s:paste['+'] = 'pbpaste'
     let s:copy['*'] = s:copy['+']