built-in add -i: start implementing the `patch` functionality in C

In the previous steps, we re-implemented the main loop of `git add -i`
in C, and most of the commands.

Notably, we left out the actual functionality of `patch`, as the
relevant code makes up more than half of `git-add--interactive.perl`,
and is actually pretty independent of the rest of the commands.

With this commit, we start to tackle that `patch` part. For better
separation of concerns, we keep the code in a separate file,
`add-patch.c`. The new code is still guarded behind the
`add.interactive.useBuiltin` config setting, and for the moment,
it can only be called via `git add -p`.

The actual functionality follows the original implementation of
5cde71d64aff (git-add --interactive, 2006-12-10), but not too closely
(for example, we use string offsets rather than copying strings around,
and after seeing whether the `k` and `j` commands are applicable, in the
C version we remember which previous/next hunk was undecided, and use it
rather than looking again when the user asked to jump).

As a further deviation from that commit, We also use a comma instead of
a slash to separate the available commands in the prompt, as the current
version of the Perl script does this, and we also add a line about the
question mark ("print help") to the help text.

While it is tempting to use this conversion of `git add -p` as an excuse
to work on `apply_all_patches()` so that it does _not_ want to read a
file from `stdin` or from a file, but accepts, say, an `strbuf` instead,
we will refrain from this particular rabbit hole at this stage.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 10 insertions, 5 deletions

diff --git a/builtin/add.c b/builtin/add.c
index d4686d5218..1deb59a642 100644
--- a/builtin/add.c
+++ b/builtin/add.c
@@ -189,12 +189,17 @@ int run_add_interactive(const char *revision, const char *patch_mode,
 	int use_builtin_add_i =
 		git_env_bool("GIT_TEST_ADD_I_USE_BUILTIN", -1);
 
-	if (!patch_mode) {
-		if (use_builtin_add_i < 0)
-			git_config_get_bool("add.interactive.usebuiltin",
-					    &use_builtin_add_i);
-		if (use_builtin_add_i == 1)
+	if (use_builtin_add_i < 0)
+		git_config_get_bool("add.interactive.usebuiltin",
+				    &use_builtin_add_i);
+
+	if (use_builtin_add_i == 1) {
+		if (!patch_mode)
 			return !!run_add_i(the_repository, pathspec);
+		if (strcmp(patch_mode, "--patch"))
+			die("'%s' not yet supported in the built-in add -p",
+			    patch_mode);
+		return !!run_add_p(the_repository, pathspec);
 	}
 
 	argv_array_push(&argv, "add--interactive");