better wsl support

autoload/firenvim.vim

@@ -108,7 +108,15 @@ function! s:get_windows_env_path(env) abort
  if l:env[0] ==# '$'
  let l:env = '%' . l:env[1:-1] . '%'
  endif
- let l:cmd_output = system(['cmd.exe', '/c', 'echo', l:env])
+ try
+ let l:cmd_output = system(['cmd.exe', '/c', 'echo', l:env])
+ catch /E475:.*cmd.exe' is not executable/
+ try
+ let l:cmd_output = system(['/mnt/c/Windows/System32/cmd.exe', '/c', 'echo', l:env])
+ catch /E475:.*cmd.exe' is not executable/
+ throw 'Error: Firenvim could not find cmd.exe from WSL on your system. Please report this issue.'
+ endtry
+ endtry
  return cmd_output[match(l:cmd_output, 'C:\\'):-3]
  endif
  throw 'Used get_windows_env_path on non-windows platform!'
@@ -746,7 +754,29 @@ function! firenvim#install(...) abort
  echo 'Creating registry key for ' . l:name . '. This may take a while. Script: ' . l:ps1_path
  call s:maybe_execute('writefile', split(l:ps1_content, "\n"), l:ps1_path)
  call s:maybe_execute('setfperm', l:ps1_path, 'rwx------')
- let o = s:maybe_execute('system', ['powershell.exe', '-Command', '-'], readfile(l:ps1_path))
+ try
+ let o = s:maybe_execute('system', ['powershell.exe', '-Command', '-'], readfile(l:ps1_path))
+ catch /powershell.exe' is not executable/
+ let l:failure = v:true
+ let l:msg = 'Error: Firenvim could not find powershell.exe'
+ " If the failure happened on wsl, try to use
+ " an absolute path
+ if s:is_wsl
+ let l:msg += ' from WSL'
+ try
+ let o = s:maybe_execute('system', ['/mnt/c/Windows/System32/WindowsPowerShell/v1.0/powershell.exe', '-Command', '-'], readfile(l:ps1_path))
+ let l:failure = v:false
+ catch /powershell.exe' is not executable/
+ let l:failure = v:true
+ endtry
+ endif
+ let l:msg += ' on your system. Please report this issue.'
+ if l:failure
+ echomsg 'Note: created ' . l:ps1_path . " . You may try to run it manually by right-clicking from your file browser to complete Firenvim's installation."
+ throw l:msg
+ endif
+ endtry
+
  if v:shell_error
  echo o
  endif