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# 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`](http://vimdoc.sourceforge.net/htmldoc/develop.html#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)
debugger.c | vim script debugger
diff.c | diff mode (vimdiff)
eval.c | expression evaluation
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
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`](https://github.com/vim/vim/blob/master/src/structs.h).
All the global variables are declared in
[`globals.h`](https://github.com/vim/vim/blob/master/src/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`](https://github.com/vim/vim/blob/master/src/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`](https://github.com/vim/vim/blob/master/src/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`](https://github.com/vim/vim/blob/master/src/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`](https://github.com/vim/vim/blob/master/src/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`](https://github.com/vim/vim/blob/master/CONTRIBUTING.md)
file.
This is `README.md` for version 8.1 of the Vim source code.
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