Merge PR #1358 'Fix python setup'

runtime/plugin/python_setup.vim

@@ -4,6 +4,14 @@ if exists("did_python_setup") || &cp
 endif
 let did_python_setup = 1
 
+" Prefix for naming things and displaying output.
+let s:plugin_name = 'Python setup'
+
+function! s:ShowError(message)
+  echohl ErrorMsg
+  echomsg s:plugin_name . ': ' . a:message . '.'
+  echohl None
+endfunction
 
 let s:get_version =
       \ ' -c "import sys; sys.stdout.write(str(sys.version_info[0]) + '.
@@ -24,23 +32,29 @@ elseif executable('python2')
   " In some distros, python3 is the default python
   let s:python_interpreter = 'python2'
 else
+  call s:ShowError('No python interpreter found')
   finish
 endif
 
+" Make sure we pick correct python version on path.
+let s:python_interpreter_path = exepath(s:python_interpreter)
+let s:python_version = systemlist(s:python_interpreter_path . ' --version')[0]
+
 " Execute python, import neovim and print a string. If import_result matches
 " the printed string, we can probably start the host
-let s:import_result = system(s:python_interpreter .
+let s:import_result = system(s:python_interpreter_path .
       \ ' -c "import neovim, sys; sys.stdout.write(\"ok\")"')
 if s:import_result != 'ok'
+  call s:ShowError('No neovim module found for ' . s:python_version)
   finish
 endif
 
-let s:pyhost_id = rpcstart(s:python_interpreter,
+let s:pyhost_id = rpcstart(s:python_interpreter_path,
       \ ['-c', 'import neovim; neovim.start_host()'])
 " Evaluate an expression in the script host as an additional sanity check, and
 " to block until all providers have been registered(or else some plugins loaded
 " by the user's vimrc would not get has('python') == 1
 if rpcrequest(s:pyhost_id, 'python_eval', '"o"+"k"') != 'ok' || !has('python')
-  " Something went wrong
+  call s:ShowError('Something went wrong setting up ' . s:python_version)
   call rpcstop(s:pyhost_id)
 endif