#5057: Avoid mixing slashes for Windows temporary files

autoload/ale/command.vim

@@ -142,7 +142,7 @@ function! s:TemporaryFilename(buffer) abort
 
     " Create a temporary filename, <temp_dir>/<original_basename>
     " The file itself will not be created by this function.
-    return ale#util#Tempname() . (s:is_windows ? '\' : '/') . l:filename
+    return ale#path#GetAbsPath(ale#util#Tempname(), l:filename)
 endfunction
 
 " Given part of a command, replace any % with %%, so that no characters in

autoload/ale/powershell.vim

@@ -8,8 +8,8 @@ function! s:TemporaryPSScript(buffer, input) abort
     " 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
+    let l:tempscript = ale#path#GetAbsPath(ale#util#Tempname(), l:filename)
+    let l:tempdir = fnamemodify(l:tempscript, ':h')
     " Create the temporary directory for the file, unreadable by 'other'
     " users.
     call mkdir(l:tempdir, '', 0750)