feat(complete): support f flag for complete buffer part

runtime/doc/news.txt

@@ -195,6 +195,8 @@ The following new APIs and features were added.
 
 • Added |vim.snippet| for snippet expansion support.
 
+• 'complete' option supports "f" flag for completing buffer names.
+
 ==============================================================================
 CHANGED FEATURES                                                 *news-changed*
 

runtime/doc/options.txt

@@ -1458,6 +1458,7 @@ A jump table for the options with a short description can be found at |Q_op|.
 		|i_CTRL-X_CTRL-D|
 	]	tag completion
 	t	same as "]"
+	f	scan the buffer names (as opposed to buffer contents)
 
 	Unloaded buffers are not loaded, thus their autocmds |:autocmd| are
 	not executed, this may lead to unexpected completions from some files

runtime/lua/vim/_meta/options.lua

@@ -998,6 +998,7 @@ vim.bo.cms = vim.bo.commentstring
 --- 	`i_CTRL-X_CTRL-D`
 --- ]	tag completion
 --- t	same as "]"
+--- f	scan the buffer names (as opposed to buffer contents)
 ---
 --- Unloaded buffers are not loaded, thus their autocmds `:autocmd` are
 --- not executed, this may lead to unexpected completions from some files

src/nvim/insexpand.c

@@ -91,6 +91,7 @@ enum {
   CTRL_X_LOCAL_MSG = 15,       ///< only used in "ctrl_x_msgs"
   CTRL_X_EVAL = 16,            ///< for builtin function complete()
   CTRL_X_CMDLINE_CTRL_X = 17,  ///< CTRL-X typed in CTRL_X_CMDLINE
+  CTRL_X_BUFNAMES = 18,
 };
 
 #define CTRL_X_MSG(i) ctrl_x_msgs[(i) & ~CTRL_X_WANT_IDENT]
@@ -536,6 +537,8 @@ bool vim_is_ctrl_x_key(int c)
     return c == Ctrl_S || c == Ctrl_P || c == Ctrl_N;
   case CTRL_X_EVAL:
     return (c == Ctrl_P || c == Ctrl_N);
+  case CTRL_X_BUFNAMES:
+    return (c == Ctrl_P || c == Ctrl_N);
   }
   internal_error("vim_is_ctrl_x_key()");
   return false;
@@ -2917,6 +2920,8 @@ static int process_next_cpt_value(ins_compl_next_state_T *st, int *compl_type_ar
       compl_type = CTRL_X_PATH_PATTERNS;
     } else if (*st->e_cpt == 'd') {
       compl_type = CTRL_X_PATH_DEFINES;
+    } else if (*st->e_cpt == 'f') {
+      compl_type = CTRL_X_BUFNAMES;
     } else if (*st->e_cpt == ']' || *st->e_cpt == 't') {
       compl_type = CTRL_X_TAGS;
       if (!shortmess(SHM_COMPLETIONSCAN)) {
@@ -3274,6 +3279,9 @@ static bool get_next_completion_match(int type, ins_compl_next_state_T *st, pos_
   case CTRL_X_SPELL:
     get_next_spell_completion(st->first_match_pos.lnum);
     break;
+  case CTRL_X_BUFNAMES:
+    get_next_bufname_token();
+    break;
 
   default:            // normal ^P/^N and ^X^L
     found_new_match = get_next_default_completion(st, ini);
@@ -3291,6 +3299,33 @@ static bool get_next_completion_match(int type, ins_compl_next_state_T *st, pos_
   return found_new_match;
 }
 
+static void get_next_bufname_token(void)
+{
+  FOR_ALL_BUFFERS(b) {
+    if (b->b_p_bl) {
+      char *start = get_past_head(b->b_sfname);
+      char *current = start;
+      char *p = (char *)path_next_component(start);
+      while (true) {
+        int len = (int)(p - current) - (*p == NUL ? 0 : 1);
+        // treat . as a separator, unless it is the first char in a filename
+        char *dot = strchr(current, '.');
+        if (dot && *p == NUL && *current != '.') {
+          len = (int)(dot - current);
+          p = dot + 1;
+        }
+        ins_compl_add(current, len, NULL, NULL, false, NULL, 0,
+                      p_ic ? CP_ICASE : 0, false);
+        if (*p == NUL) {
+          break;
+        }
+        current = p;
+        p = (char *)path_next_component(p);
+      }
+    }
+  }
+}
+
 /// Get the next expansion(s), using "compl_pattern".
 /// The search starts at position "ini" in curbuf and in the direction
 /// compl_direction.

src/nvim/options.lua

@@ -1370,6 +1370,7 @@ return {
         	|i_CTRL-X_CTRL-D|
         ]	tag completion
         t	same as "]"
+        f	scan the buffer names (as opposed to buffer contents)
 
         Unloaded buffers are not loaded, thus their autocmds |:autocmd| are
         not executed, this may lead to unexpected completions from some files

src/nvim/optionstr.c

@@ -1171,7 +1171,7 @@ const char *did_set_complete(optset_T *args)
     if (!*s) {
       break;
     }
-    if (vim_strchr(".wbuksid]tU", (uint8_t)(*s)) == NULL) {
+    if (vim_strchr(".wbuksid]tUf", (uint8_t)(*s)) == NULL) {
       return illegal_char(args->os_errbuf, args->os_errbuflen, (uint8_t)(*s));
     }
     if (*++s != NUL && *s != ',' && *s != ' ') {
@@ -1200,7 +1200,7 @@ const char *did_set_complete(optset_T *args)
 int expand_set_complete(optexpand_T *args, int *numMatches, char ***matches)
 {
   static char *(p_cpt_values[]) = {
-    ".", "w", "b", "u", "k", "kspell", "s", "i", "d", "]", "t", "U", NULL
+    ".", "w", "b", "u", "k", "kspell", "s", "i", "d", "]", "t", "U", "f", NULL
   };
   return expand_set_opt_string(args,
                                p_cpt_values,

test/functional/editor/completion_spec.lua

@@ -1228,4 +1228,28 @@ describe('completion', function()
     expect('colorscheme NOSUCHCOLORSCHEME')
     assert_alive()
   end)
+
+  it('complete with f flag #25598', function()
+    screen:try_resize(20, 9)
+    local bufname = 'foo/bar.txt'
+    local hidden = 'fooA/.hidden'
+    if helpers.is_os('win') then
+      bufname = 'C:\\foo\\bar.txt'
+      hidden = 'C:\\fooA\\.hidden'
+    end
+    command('set complete+=f | edit '.. bufname ..' | edit '..hidden)
+    feed('i<C-n>')
+
+    screen:expect{grid=[[
+      foo^                 |
+      {2:foo            }{0:     }|
+      {1:bar            }{0:     }|
+      {1:txt            }{0:     }|
+      {1:fooA           }{0:     }|
+      {1:.hidden        }{0:     }|
+      {0:~                   }|
+      {0:~                   }|
+      {3:-- }{4:match 1 of 5}     |
+    ]]}
+  end)
 end)