vim-patch:8.0.1649: no completion for argument list commands

Problem:    No completion for argument list commands.
Solution:   Add arglist completion. (Yegappan Lakshmanan, closes vim/vim#2706)
cd43effeca

runtime/doc/eval.txt

@@ -4079,6 +4079,7 @@ getcompletion({pat}, {type} [, {filtered}])		*getcompletion()*
 		specifies what for.  The following completion types are
 		supported:
 
+		arglist		file names in argument list
 		augroup		autocmd groups
 		buffer		buffer names
 		behave		:behave suboptions

runtime/doc/map.txt

@@ -1208,6 +1208,7 @@ By default, the arguments of user defined commands do not undergo completion.
 However, by specifying one or the other of the following attributes, argument
 completion can be enabled:
 
+	-complete=arglist	file names in argument list
 	-complete=augroup	autocmd groups
 	-complete=buffer	buffer names
 	-complete=behave	:behave suboptions

src/nvim/ex_cmds2.c

@@ -2254,6 +2254,15 @@ static int alist_add_list(int count, char_u **files, int after)
   }
 }
 
+// Function given to ExpandGeneric() to obtain the possible arguments of the
+// argedit and argdelete commands.
+char_u *get_arglist_name(expand_T *xp FUNC_ATTR_UNUSED, int idx)
+{
+  if (idx >= ARGCOUNT) {
+    return NULL;
+  }
+  return alist_name(&ARGLIST[idx]);
+}
 
 /// ":compiler[!] {name}"
 void ex_compiler(exarg_T *eap)

src/nvim/ex_docmd.c

@@ -3454,6 +3454,13 @@ const char * set_one_cmd_context(
     xp->xp_pattern = (char_u *)arg;
     break;
 
+  case CMD_argdelete:
+    while ((xp->xp_pattern = vim_strchr((const char_u *)arg, ' ')) != NULL) {
+      arg = (const char *)(xp->xp_pattern + 1);
+    }
+    xp->xp_context = EXPAND_ARGLIST;
+    xp->xp_pattern = (char_u *)arg;
+    break;
 
   default:
     break;
@@ -4859,6 +4866,7 @@ static struct {
  */
 static const char *command_complete[] =
 {
+  [EXPAND_ARGLIST] = "arglist",
   [EXPAND_AUGROUP] = "augroup",
   [EXPAND_BEHAVE] = "behave",
   [EXPAND_BUFFERS] = "buffer",

src/nvim/ex_getln.c

@@ -4784,6 +4784,7 @@ ExpandFromContext (
 #endif
       { EXPAND_ENV_VARS, get_env_name, true, true },
       { EXPAND_USER, get_users, true, false },
+      { EXPAND_ARGLIST, get_arglist_name, true, false },
     };
     int i;
 

src/nvim/testdir/test_cmdline.vim

@@ -137,6 +137,11 @@ func Test_getcompletion()
   let l = getcompletion('v:notexists', 'var')
   call assert_equal([], l)
 
+  args a.c b.c
+  let l = getcompletion('', 'arglist')
+  call assert_equal(['a.c', 'b.c'], l)
+  %argdelete
+
   let l = getcompletion('', 'augroup')
   call assert_true(index(l, 'END') >= 0)
   let l = getcompletion('blahblah', 'augroup')

src/nvim/vim.h

@@ -156,6 +156,7 @@ enum {
   EXPAND_PACKADD,
   EXPAND_MESSAGES,
   EXPAND_MAPCLEAR,
+  EXPAND_ARGLIST,
   EXPAND_CHECKHEALTH,
 };