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 --------- | ----------- autocmd.c | autocommands buffer.c | manipulating buffers (loaded files) change.c | handling changes to text debugger.c | vim script debugger diff.c | diff mode (vimdiff) eval.c | expression evaluation evalfunc.c | built-in functions fileio.c | reading and writing files findfile.c | search for files in 'path' fold.c | folding getchar.c | getting characters and key mapping indent.c | C and Lisp indentation insexpand.c | Insert mode completion mark.c | marks 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 ops.c | handling operators ("d", "y", "p") option.c | options quickfix.c | quickfix commands (":make", ":cn") regexp.c | pattern matching screen.c | updating the windows search.c | pattern searching sign.c | signs spell.c | spell checking syntax.c | syntax and other highlighting tag.c | tags term.c | terminal handling, termcap codes undo.c | undo and redo usercmd.c | user defined commands userfunc.c | user defined functions 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 8.1 of the Vim source code.