Linter for powershell syntax errors (#2413)

* Linter for powershell syntax errors

autoload/ale/powershell.vim

@@ -0,0 +1,32 @@
+" Author: zigford <zigford@gmail.com>
+" Description: Functions for integrating with Powershell linters.
+
+" Write a powershell script to a temp file for execution
+" return the command used to execute it
+function! s:TemporaryPSScript(buffer, input) abort
+    let l:filename = 'script.ps1'
+    " Create a temp dir to house our temp .ps1 script
+    " a temp dir is needed as powershell needs the .ps1
+    " extension
+    let l:tempdir = ale#util#Tempname() . (has('win32') ? '\' : '/')
+    let l:tempscript = l:tempdir . l:filename
+    " Create the temporary directory for the file, unreadable by 'other'
+    " users.
+    call mkdir(l:tempdir, '', 0750)
+    " Automatically delete the directory later.
+    call ale#command#ManageDirectory(a:buffer, l:tempdir)
+    " Write the script input out to a file.
+    call ale#util#Writefile(a:buffer, a:input, l:tempscript)
+
+    return l:tempscript
+endfunction
+
+function! ale#powershell#RunPowerShell(buffer, base_var_name, command) abort
+    let l:executable = ale#Var(a:buffer, a:base_var_name . '_executable')
+    let l:tempscript = s:TemporaryPSScript(a:buffer, a:command)
+
+    return ale#Escape(l:executable)
+    \ . ' -Exe Bypass -NoProfile -File '
+    \ . ale#Escape(l:tempscript)
+    \ . ' %t'
+endfunction