Add a function for parsing command args

autoload/ale/args.vim

@@ -0,0 +1,43 @@
+" Author: w0rp <devw0rp@gmail.com>
+" Description: This module implements a function for parsing arguments for
+" commands.
+
+" Given a list of valid arguments like ['foo', 'bar'] and a string to parse,
+" parse the arguments from the string and return [parsed_args, remainder].
+"
+" Arguments must be prefixed in the string with a single minus (-), and a
+" double minus (--) denotes the end of arguments.
+function! ale#args#Parse(arg_list, string) abort
+    let l:parsed = {}
+    let l:end_of_args = 0
+    let l:word_list = split(a:string, ' ')
+    let l:index = 0
+
+    while l:index < len(l:word_list)
+        let l:word = l:word_list[l:index]
+
+        if l:word[:0] is# '-'
+            let l:index += 1
+
+            if l:word is# '--'
+                break
+            endif
+
+            let l:arg = l:word[1:]
+
+            if index(a:arg_list, l:arg) >= 0
+                let l:parsed[l:arg] = ''
+            else
+                throw 'Invalid argument: ' . l:word
+            endif
+        elseif l:word is# ''
+            let l:index += 1
+        else
+            break
+        endif
+    endwhile
+
+    let l:new_string = join(l:word_list[l:index :], ' ')
+
+    return [l:parsed, l:new_string]
+endfunction

test/test_parse_command_args.vader

@@ -0,0 +1,52 @@
+After:
+  unlet! b:parse_result
+
+  if exists(':ParseTest')
+    delcommand ParseTest
+  endif
+
+Execute(ale#args#Parse should handle empty input):
+  AssertEqual
+  \ [{}, ''],
+  \ ale#args#Parse([], '')
+  AssertEqual
+  \ [{}, ''],
+  \ ale#args#Parse(['foo', 'bar'], '')
+
+Execute(ale#args#Parse should parse commands correctly):
+  AssertEqual
+  \ [{'foo': '', 'bar': ''}, 'leave  these  alone'],
+  \ ale#args#Parse(['foo', 'bar'], '-foo   -bar  leave  these  alone')
+  AssertEqual
+  \ [{'foo': ''}, 'leave  these  alone'],
+  \ ale#args#Parse(['foo', 'bar'], '-foo   leave  these  alone')
+
+Execute(ale#args#Parse should raise errors for unknown arguments):
+  AssertThrows call ale#args#Parse(['foo', 'bar'], '-nope   leave  these  alone')
+  AssertEqual 'Invalid argument: -nope', g:vader_exception
+
+Execute(ale#args#Parse should stop parsing arguments after --):
+  AssertEqual
+  \ [{'foo': ''}, ' --nope  leave  these  alone'],
+  \ ale#args#Parse(['foo', 'bar'], '-foo --  --nope  leave  these  alone')
+  AssertEqual
+  \ [{}, '--'],
+  \ ale#args#Parse(['foo', 'bar'], '-- --')
+  AssertEqual
+  \ [{}, ''],
+  \ ale#args#Parse(['foo', 'bar'], '--')
+
+Execute(ale#args#Parse should work for an example command):
+  command! -nargs=* ParseTest let b:parse_result = ale#args#Parse(['foo', 'bar'], <q-args>)
+
+  ParseTest
+  AssertEqual [{}, ''], b:parse_result
+
+  ParseTest -foo
+  AssertEqual [{'foo': ''}, ''], b:parse_result
+
+  ParseTest -foo -bar
+  AssertEqual [{'foo': '', 'bar': ''}, ''], b:parse_result
+
+  ParseTest -foo -bar leave  these  alone
+  AssertEqual [{'foo': '', 'bar': ''}, 'leave  these  alone'], b:parse_result