Close #2281 - Separate cwd commands from commands

Working directories are now set seperately from the commands so they
can later be swapped out when running linters over projects is
supported, and also better support filename mapping for running linters
on other machines in future.

autoload/ale/ant.vim

@@ -23,19 +23,23 @@ function! ale#ant#FindExecutable(buffer) abort
     return ''
 endfunction
 
-" Given a buffer number, build a command to print the classpath of the root
-" project. Returns an empty string if cannot build the command.
+" Given a buffer number, get a working directory and command to print the
+" classpath of the root project.
+"
+" Returns an empty string for the command if Ant is not detected.
 function! ale#ant#BuildClasspathCommand(buffer) abort
     let l:executable = ale#ant#FindExecutable(a:buffer)
-    let l:project_root = ale#ant#FindProjectRoot(a:buffer)
 
-    if !empty(l:executable) && !empty(l:project_root)
-        return ale#path#CdString(l:project_root)
-        \   . ale#Escape(l:executable)
-        \   . ' classpath'
-        \   . ' -S'
-        \   . ' -q'
+    if !empty(l:executable)
+        let l:project_root = ale#ant#FindProjectRoot(a:buffer)
+
+        if !empty(l:project_root)
+            return [
+            \   l:project_root,
+            \   ale#Escape(l:executable) .' classpath -S -q'
+            \]
+        endif
     endif
 
-    return ''
+    return ['', '']
 endfunction