refactor: rewrite clipboard provider healthchecks in Lua

This is required to remove the vimscript checkhealth functions.

runtime/autoload/health/provider2.vim

@@ -122,31 +122,6 @@ function! s:download(url) abort
           \ .'and `python`, cannot make web request'
 endfunction
 
-" Check for clipboard tools.
-function! s:check_clipboard() abort
-  call health#report_start('Clipboard (optional)')
-
-  if !empty($TMUX) && executable('tmux') && executable('pbpaste') && !s:cmd_ok('pbpaste')
-    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(
-          \ provider#clipboard#Error(),
-          \ ["Use the example in :help g:clipboard as a template, or don't set g:clipboard at all."])
-  elseif empty(clipboard_tool)
-    call health#report_warn(
-          \ 'No clipboard tool found. Clipboard registers (`"+` and `"*`) will not work.',
-          \ [':help clipboard'])
-  else
-    call health#report_ok('Clipboard tool found: '. clipboard_tool)
-  endif
-endfunction
-
 " Get the latest Nvim Python client (pynvim) version from PyPI.
 function! s:latest_pypi_version() abort
   let pypi_version = 'unable to get pypi response'
@@ -745,8 +720,7 @@ function! s:check_perl() abort
   endif
 endfunction
 
-function! health#provider#check() abort
-  call s:check_clipboard()
+function! health#provider2#check() abort
   call s:check_python()
   call s:check_virtualenv()
   call s:check_ruby()

runtime/lua/provider/health.lua

@@ -0,0 +1,55 @@
+local M = {}
+
+-- Returns true if `cmd` exits with success, else false.
+local function cmd_ok(cmd)
+  vim.fn.system(cmd)
+  return vim.v.shell_error == 0
+end
+
+local function executable(exe)
+  return vim.fn.executable(exe) == 1
+end
+
+local function is_blank(s)
+  return s:find('^%s*$') ~= nil
+end
+
+local function clipboard()
+  vim.health.report_start('Clipboard (optional)')
+
+  if
+    os.getenv('TMUX')
+    and executable('tmux')
+    and executable('pbpaste')
+    and not cmd_ok('pbpaste')
+  then
+    local tmux_version = string.match(vim.fn.system('tmux -V'), '%d+%.%d+')
+    local advice = {
+      'Install tmux 2.6+.  https://superuser.com/q/231130',
+      'or use tmux with reattach-to-user-namespace.  https://superuser.com/a/413233',
+    }
+    vim.health.report_error('pbcopy does not work with tmux version: ' .. tmux_version, advice)
+  end
+
+  local clipboard_tool = vim.fn['provider#clipboard#Executable']()
+  if vim.g.clipboard and is_blank(clipboard_tool) then
+    local error_message = vim.fn['provider#clipboard#Error']()
+    vim.health.report_error(
+      error_message,
+      "Use the example in :help g:clipboard as a template, or don't set g:clipboard at all."
+    )
+  elseif is_blank(clipboard_tool) then
+    vim.health.report_warn(
+      'No clipboard tool found. Clipboard registers (`"+` and `"*`) will not work.',
+      ':help clipboard'
+    )
+  else
+    vim.health.report_ok('Clipboard tool found: ' .. clipboard_tool)
+  end
+end
+
+function M.check()
+  clipboard()
+end
+
+return M