Documentation/technical/api-builtin.txt

   1 builtin API
   2 ===========
   3
   4 Adding a new built-in
   5 ---------------------
   6
   7 There are 4 things to do to add a built-in command implementation to
   8 git:
   9
  10 . Define the implementation of the built-in command `foo` with
  11   signature:
  12
  13         int cmd_foo(int argc, const char **argv, const char *prefix);
  14
  15 . Add the external declaration for the function to `builtin.h`.
  16
  17 . Add the command to `commands[]` table in `handle_internal_command()`,
  18   defined in `git.c`.  The entry should look like:
  19
  20         { "foo", cmd_foo, <options> },
  21 +
  22 where options is the bitwise-or of:
  23
  24 `RUN_SETUP`::
  25
  26         Make sure there is a git directory to work on, and if there is a
  27         work tree, chdir to the top of it if the command was invoked
  28         in a subdirectory.  If there is no work tree, no chdir() is
  29         done.
  30
  31 `USE_PAGER`::
  32
  33         If the standard output is connected to a tty, spawn a pager and
  34         feed our output to it.
  35
  36 `NEED_WORK_TREE`::
  37
  38         Make sure there is a work tree, i.e. the command cannot act
  39         on bare repositories.
  40         This only makes sense when `RUN_SETUP` is also set.
  41
  42 . Add `builtin-foo.o` to `BUILTIN_OBJS` in `Makefile`.
  43
  44 Additionally, if `foo` is a new command, there are 3 more things to do:
  45
  46 . Add tests to `t/` directory.
  47
  48 . Write documentation in `Documentation/git-foo.txt`.
  49
  50 . Add an entry for `git-foo` to `command-list.txt`.
  51
  52 . Add an entry for `/git-foo` to `.gitignore`.
  53
  54
  55 How a built-in is called
  56 ------------------------
  57
  58 The implementation `cmd_foo()` takes three parameters, `argc`, `argv,
  59 and `prefix`.  The first two are similar to what `main()` of a
  60 standalone command would be called with.
  61
  62 When `RUN_SETUP` is specified in the `commands[]` table, and when you
  63 were started from a subdirectory of the work tree, `cmd_foo()` is called
  64 after chdir(2) to the top of the work tree, and `prefix` gets the path
  65 to the subdirectory the command started from.  This allows you to
  66 convert a user-supplied pathname (typically relative to that directory)
  67 to a pathname relative to the top of the work tree.
  68
  69 The return value from `cmd_foo()` becomes the exit status of the
  70 command.