af9a7a04f1
Problem: cannot perform autocompletion
Solution: Add the 'autocomplete' option value
(Girish Palya)
This change introduces the 'autocomplete' ('ac') boolean option to
enable automatic popup menu completion during insert mode. When enabled,
Vim shows a completion menu as you type, similar to pressing |i\_CTRL-N|
manually. The items are collected from sources defined in the
'complete' option.
To ensure responsiveness, this feature uses a time-sliced strategy:
- Sources earlier in the 'complete' list are given more time.
- If a source exceeds its allocated timeout, it is interrupted.
- The next source is then started with a reduced timeout (exponentially
decayed).
- A small minimum ensures every source still gets a brief chance to
contribute.
The feature is fully compatible with other |i_CTRL-X| completion modes,
which can temporarily suspend automatic completion when triggered.
See :help 'autocomplete' and :help ins-autocompletion for more details.
To try it out, use :set ac
You should see a popup menu appear automatically with suggestions. This
works seamlessly across:
- Large files (multi-gigabyte size)
- Massive codebases (:argadd thousands of .c or .h files)
- Large dictionaries via the `k` option
- Slow or blocking LSP servers or user-defined 'completefunc'
Despite potential slowness in sources, the menu remains fast,
responsive, and useful.
Compatibility: This mode is fully compatible with existing completion
methods. You can still invoke any CTRL-X based completion (e.g.,
CTRL-X CTRL-F for filenames) at any time (CTRL-X temporarily
suspends 'autocomplete'). To specifically use i_CTRL-N, dismiss the
current popup by pressing CTRL-E first.
---
How it works
To keep completion snappy under all conditions, autocompletion uses a
decaying time-sliced algorithm:
- Starts with an initial timeout (80ms).
- If a source does not complete within the timeout, it's interrupted and
the timeout is halved for the next source.
- This continues recursively until a minimum timeout (5ms) is reached.
- All sources are given a chance, but slower ones are de-prioritized
quickly.
Most of the time, matches are computed well within the initial window.
---
Implementation details
- Completion logic is mostly triggered in `edit.c` and handled in
insexpand.c.
- Uses existing inc_compl_check_keys() mechanism, so no new polling
hooks are needed.
- The completion system already checks for user input periodically; it
now also checks for timer expiry.
---
Design notes
- The menu doesn't continuously update after it's shown to prevent
visual distraction (due to resizing) and ensure the internal list
stays synchronized with the displayed menu.
- The 'complete' option determines priority—sources listed earlier get
more time.
- The exponential time-decay mechanism prevents indefinite collection,
contributing to low CPU usage and a minimal memory footprint.
- Timeout values are intentionally not configurable—this system is
optimized to "just work" out of the box. If autocompletion feels slow,
it typically indicates a deeper performance bottleneck (e.g., a slow
custom function not using `complete_check()`) rather than a
configuration issue.
---
Performance
Based on testing, the total roundtrip time for completion is generally
under 200ms. For common usage, it often responds in under 50ms on an
average laptop, which falls within the "feels instantaneous" category
(sub-100ms) for perceived user experience.
| Upper Bound (ms) | Perceived UX
|----------------- |-------------
| <100 ms | Excellent; instantaneous
| <200 ms | Good; snappy
| >300 ms | Noticeable lag
| >500 ms | Sluggish/Broken
---
Why this belongs in core:
- Minimal and focused implementation, tightly integrated with existing
Insert-mode completion logic.
- Zero reliance on autocommands and external scripting.
- Makes full use of Vim’s highly composable 'complete' infrastructure
while avoiding the complexity of plugin-based solutions.
- Gives users C native autocompletion with excellent responsiveness and
no configuration overhead.
- Adds a key UX functionality in a simple, performant, and Vim-like way.
closes: #17812
Signed-off-by: Girish Palya <girishji@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
Vim source code
Here are a few hints for finding your way around the source code. This doesn't make it less complex than it is, but it gets you started.
You might also want to read
:help development.
Jumping around
First of all, use :make tags to generate a tags file, so that you can jump
around in the source code.
To jump to a function or variable definition, move the cursor on the name and
use the CTRL-] command. Use CTRL-T or CTRL-O to jump back.
To jump to a file, move the cursor on its name and use the gf command.
Most code can be found in a file with an obvious name (incomplete list):
| File name | Description |
|---|---|
| alloc.c | memory management |
| arglist.c | handling argument list |
| autocmd.c | autocommands |
| blob.c | blob data type |
| buffer.c | manipulating buffers (loaded files) |
| bufwrite.c | writing a buffer to file |
| change.c | handling changes to text |
| cindent.c | C and Lisp indentation |
| clientserver.c | client server functionality |
| clipboard.c | handling the clipboard |
| cmdexpand.c | command-line completion |
| cmdhist.c | command-line history |
| debugger.c | Vim script debugger |
| diff.c | diff mode (vimdiff) |
| drawline.c | drawing a window line |
| drawscreen.c | drawing the windows |
| eval.c | expression evaluation |
| evalbuffer.c | buffer related built-in functions |
| evalfunc.c | built-in functions |
| evalvars.c | vim variables |
| evalwindow.c | window related built-in functions |
| fileio.c | reading and writing files |
| filepath.c | dealing with file names and paths |
| findfile.c | search for files in 'path' |
| fold.c | folding |
| getchar.c | getting characters and key mapping |
| gc.c | garbage collection |
| help.c | vim help related functions |
| highlight.c | syntax highlighting |
| indent.c | text indentation |
| insexpand.c | Insert mode completion |
| locale.c | locale/language handling |
| map.c | mapping and abbreviations |
| mark.c | marks |
| match.c | highlight matching |
| float.c | floating point functions |
| mbyte.c | multi-byte character handling |
| memfile.c | storing lines for buffers in a swapfile |
| memline.c | storing lines for buffers in memory |
| menu.c | menus |
| message.c | (error) messages |
| mouse.c | handling the mouse |
| ops.c | handling operators ("d", "y", "p") |
| option.c | options |
| optionstr.c | handling string options |
| popupmenu.c | popup menu |
| popupwin.c | popup window |
| profiler.c | Vim script profiler |
| quickfix.c | quickfix commands (":make", ":cn") |
| regexp.c | pattern matching |
| register.c | handling registers |
| scriptfile.c | runtime directory handling and sourcing scripts |
| screen.c | lower level screen functions |
| search.c | pattern searching |
| session.c | sessions and views |
| sign.c | signs |
| spell.c | spell checking core |
| spellfile.c | spell file handling |
| spellsuggest.c | spell correction suggestions |
| strings.c | string manipulation functions |
| syntax.c | syntax and other highlighting |
| tag.c | tags |
| term.c | terminal handling, termcap codes |
| testing.c | testing: assert and test functions |
| textformat.c | text formatting |
| textobject.c | text objects |
| textprop.c | text properties |
| time.c | time and timer functions |
| typval.c | Vim script type/value functions |
| undo.c | undo and redo |
| usercmd.c | user defined commands |
| userfunc.c | user defined functions |
| viminfo.c | viminfo handling |
| window.c | handling split windows |
Debugging
If you have a reasonable recent version of gdb, you can use the :Termdebug
command to debug Vim. See :help :Termdebug.
When something is time critical or stepping through code is a hassle, use the channel logging to create a time-stamped log file. Add lines to the code like this:
ch_log(NULL, "Value is now %02x", value);
After compiling and starting Vim, do:
:call ch_logfile('debuglog', 'w')
And edit debuglog to see what happens. The channel functions already have
ch_log() calls, thus you always see that in the log.
Important Variables
The current mode is stored in State. The values it can have are NORMAL,
INSERT, CMDLINE, and a few others.
The current window is curwin. The current buffer is curbuf. These point
to structures with the cursor position in the window, option values, the file
name, etc. These are defined in
structs.h.
All the global variables are declared in
globals.h.
The main loop
This is conveniently called main_loop(). It updates a few things and then
calls normal_cmd() to process a command. This returns when the command is
finished.
The basic idea is that Vim waits for the user to type a character and
processes it until another character is needed. Thus there are several places
where Vim waits for a character to be typed. The vgetc() function is used
for this. It also handles mapping.
Updating the screen is mostly postponed until a command or a sequence of
commands has finished. The work is done by update_screen(), which calls
win_update() for every window, which calls win_line() for every line.
See the start of
screen.c
for more explanations.
Command-line mode
When typing a :, normal_cmd() will call getcmdline() to obtain a line
with an Ex command. getcmdline() contains a loop that will handle each typed
character. It returns when hitting CR or Esc or some other character that
ends the command line mode.
Ex commands
Ex commands are handled by the function do_cmdline(). It does the generic
parsing of the : command line and calls do_one_cmd() for each separate
command. It also takes care of while loops.
do_one_cmd() parses the range and generic arguments and puts them in the
exarg_t and passes it to the function that handles the command.
The : commands are listed in ex_cmds.h. The third entry of each item is
the name of the function that handles the command. The last entry are the
flags that are used for the command.
Normal mode commands
The Normal mode commands are handled by the normal_cmd() function. It also
handles the optional count and an extra character for some commands. These
are passed in a cmdarg_t to the function that handles the command.
There is a table nv_cmds in
normal.c
which lists the first character of every command. The second entry of each
item is the name of the function that handles the command.
Insert mode commands
When doing an i or a command, normal_cmd() will call the edit()
function. It contains a loop that waits for the next character and handles it.
It returns when leaving Insert mode.
Options
There is a list with all option names in
option.c,
called options[].
The GUI
Most of the GUI code is implemented like it was a clever terminal. Typing a
character, moving a scrollbar, clicking the mouse, etc. are all translated
into events which are written in the input buffer. These are read by the
main code, just like reading from a terminal. The code for this is scattered
through gui.c.
For example, gui_send_mouse_event() for a mouse click and gui_menu_cb() for
a menu action. Key hits are handled by the system-specific GUI code, which
calls add_to_input_buf() to send the key code.
Updating the GUI window is done by writing codes in the output buffer, just
like writing to a terminal. When the buffer gets full or is flushed,
gui_write() will parse the codes and draw the appropriate items. Finally the
system-specific GUI code will be called to do the work.
Debugging the GUI
Remember to prevent that gvim forks and the debugger thinks Vim has exited,
add the -f argument. In gdb: run -f -g.
When stepping through display updating code, the focus event is triggered
when going from the debugger to Vim and back. To avoid this, recompile with
some code in gui_focus_change() disabled.
Contributing
If you would like to help making Vim better, see the
CONTRIBUTING.md
file.
This is README.md for version 9.1 of the Vim source code.