Feature/add ant support (#2539)

Use ant files to load Java settings too.

autoload/ale/ant.vim

@@ -0,0 +1,41 @@
+" Author: Andrew Lee <andrewl@mbda.fun>.
+" Inspired by ale/gradle.vim by Michael Pardo <michael@michaelpardo.com>
+" Description: Functions for working with Ant projects.
+
+" Given a buffer number, find an Ant project root
+function! ale#ant#FindProjectRoot(buffer) abort
+    let l:build_xml_path = ale#path#FindNearestFile(a:buffer, 'build.xml')
+
+    if !empty(l:build_xml_path)
+        return fnamemodify(l:build_xml_path, ':h')
+    endif
+
+    return ''
+endfunction
+
+" Given a buffer number, find the path to the `ant` executable. Returns an empty
+" string if cannot find the executable.
+function! ale#ant#FindExecutable(buffer) abort
+    if executable('ant')
+        return 'ant'
+    endif
+
+    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.
+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'
+    endif
+
+    return ''
+endfunction

autoload/ale/java.vim

@@ -16,5 +16,11 @@ function! ale#java#FindProjectRoot(buffer) abort
         return fnamemodify(l:maven_pom_file, ':h')
     endif
 
+    let l:ant_root = ale#ant#FindProjectRoot(a:buffer)
+
+    if !empty(l:ant_root)
+        return l:ant_root
+    endif
+
     return ''
 endfunction