Edit File: api-builtin.txt
builtin API =========== Adding a new built-in --------------------- There are 4 things to do to add a built-in command implementation to Git: . Define the implementation of the built-in command `foo` with signature: int cmd_foo(int argc, const char **argv, const char *prefix); . Add the external declaration for the function to `builtin.h`. . Add the command to `commands[]` table in `handle_internal_command()`, defined in `git.c`. The entry should look like: { "foo", cmd_foo, <options> }, + where options is the bitwise-or of: `RUN_SETUP`:: Make sure there is a Git directory to work on, and if there is a work tree, chdir to the top of it if the command was invoked in a subdirectory. If there is no work tree, no chdir() is done. `USE_PAGER`:: If the standard output is connected to a tty, spawn a pager and feed our output to it. `NEED_WORK_TREE`:: Make sure there is a work tree, i.e. the command cannot act on bare repositories. This only makes sense when `RUN_SETUP` is also set. . Add `builtin-foo.o` to `BUILTIN_OBJS` in `Makefile`. Additionally, if `foo` is a new command, there are 3 more things to do: . Add tests to `t/` directory. . Write documentation in `Documentation/git-foo.txt`. . Add an entry for `git-foo` to `command-list.txt`. . Add an entry for `/git-foo` to `.gitignore`. How a built-in is called ------------------------ The implementation `cmd_foo()` takes three parameters, `argc`, `argv, and `prefix`. The first two are similar to what `main()` of a standalone command would be called with. When `RUN_SETUP` is specified in the `commands[]` table, and when you were started from a subdirectory of the work tree, `cmd_foo()` is called after chdir(2) to the top of the work tree, and `prefix` gets the path to the subdirectory the command started from. This allows you to convert a user-supplied pathname (typically relative to that directory) to a pathname relative to the top of the work tree. The return value from `cmd_foo()` becomes the exit status of the command.