provider/pythonx: Don't use Python 3 interpreter for +python.

The executable 'python' can refer to either Python 2 or Python 3. Add a
check to only accept Python 2 interpreters as providers for +python.

Also improve the error messages.

Resolves #2734.

1 files changed, 33 insertions, 25 deletions

diff --git a/runtime/autoload/provider/pythonx.vim b/runtime/autoload/provider/pythonx.vim
index b1e6ff9e3a..b08a6dbf91 100644
--- a/runtime/autoload/provider/pythonx.vim
+++ b/runtime/autoload/provider/pythonx.vim
@@ -5,55 +5,62 @@ endif
 
 let s:loaded_pythonx_provider = 1
 
-function! provider#pythonx#Detect(ver) abort
-  let host_var = (a:ver == 2) ?
+function! provider#pythonx#Detect(major_ver) abort
+  let host_var = (a:major_ver == 2) ?
         \ 'g:python_host_prog' : 'g:python3_host_prog'
-  let skip_var = (a:ver == 2) ?
+  let skip_var = (a:major_ver == 2) ?
         \ 'g:python_host_skip_check' : 'g:python3_host_skip_check'
   let skip = exists(skip_var) ? {skip_var} : 0
   if exists(host_var)
     " Disable auto detection.
-    let [check, err, _] = s:check_interpreter({host_var}, a:ver, skip)
-    if check
+    let [result, err, _] = s:check_interpreter({host_var}, a:major_ver, skip)
+    if result
       return [{host_var}, err]
     endif
-    return ['', 'provider#pythonx#Detect: could not load Python '.a:ver
-          \ .' (from '.host_var.'): '.err]
+    return ['', 'provider/pythonx: Could not load Python ' . a:major_ver
+          \ . ' from ' . host_var . ': ' . err]
   endif
 
-  let detect_versions = (a:ver == 2) ?
+  let prog_suffixes = (a:major_ver == 2) ?
         \   ['2', '2.7', '2.6', '']
         \ : ['3', '3.5', '3.4', '3.3', '']
 
-  for prog in map(detect_versions, "'python' . v:val")
-    let [check, err, ver] = s:check_interpreter(prog, a:ver, skip)
-    if check
-      let [check, err] = s:check_version(prog, ver, skip)
-      if check
+  let errors = []
+  for prog in map(prog_suffixes, "'python' . v:val")
+    let [result, err, prog_ver] = s:check_interpreter(prog, a:major_ver, skip)
+    if result
+      let [result, err] = s:check_version(prog, prog_ver, a:major_ver, skip)
+      if result
         return [prog, err]
       endif
     endif
+
+    " Accumulate errors in case we don't find
+    " any suitable Python interpreter.
+    call add(errors, err)
   endfor
 
-  return ['', 'provider#pythonx#Detect: could not load Python '.a:ver
-        \ .': '.err]
+  " No suitable Python interpreter found.
+  return ['', 'provider/pythonx: Could not load Python ' . a:major_ver
+        \ . ":\n" .  join(errors, "\n")]
 endfunction
 
-function! s:check_version(prog, ver, skip) abort
+function! s:check_version(prog, prog_ver, major_ver, skip) abort
   if a:skip
     return [1, '']
   endif
 
-  let min_version = (a:ver[0] == 2) ? '2.6' : '3.3'
-  if a:ver >= min_version
+  let min_version = (a:major_ver == 2) ? '2.6' : '3.3'
+  if a:prog_ver =~ '^' . a:major_ver && a:prog_ver >= min_version
     return [1, '']
   endif
-  return [0, 'Python ' . a:ver . ' interpreter is not supported.']
+  return [0, a:prog . ' is Python ' . prog_ver . ' and cannot provide Python '
+        \ . a:major_ver . '.']
 endfunction
 
-function! s:check_interpreter(prog, ver, skip) abort
+function! s:check_interpreter(prog, major_ver, skip) abort
   if !executable(a:prog)
-    return [0, 'Python'.a:ver.' interpreter is not executable.', '']
+    return [0, a:prog . ' does not exist or is not executable.', '']
   endif
 
   if a:skip
@@ -61,16 +68,17 @@ function! s:check_interpreter(prog, ver, skip) abort
   endif
 
   " Try to load neovim module, and output Python version.
-  let ver = system(a:prog . ' -c ' .
+  let prog_ver = system(a:prog . ' -c ' .
         \ '''import sys; sys.stdout.write(str(sys.version_info[0]) + '.
         \ '"." + str(sys.version_info[1])); '''.
-        \ (a:ver == 2 ?
+        \ (a:major_ver == 2 ?
         \   '''import pkgutil; exit(pkgutil.get_loader("neovim") is None)''':
         \   '''import importlib; exit(importlib.find_loader("neovim") is None)''')
         \ )
   if v:shell_error
-    return [0, 'Python'.a:ver.' interpreter ('.a:prog.') has no neovim module installed. See ":help nvim-python".', ver]
+    return [0, a:prog  . ' does have not have the neovim module installed. '
+          \ . 'See ":help nvim-python".', prog_ver]
   endif
-  return [1, '', ver]
+  return [1, '', prog_ver]
 endfunction