[PATCH v4 4/4] builtin/rebase: support running "git rebase <upstream>"

[Pratik Karki <predatoramigo@gmail.com>]

This patch gives life to the skeleton added in the previous patches:
With this change, we can perform a elementary rebase (without any
options).

It can be tested thusly by:

git -c rebase.usebuiltin=true rebase HEAD~2

The rebase backends (i.e. the shell script functions defined in
`git-rebase--<backend>`) are still at work here and the "builtin
rebase"'s purpose is simply to parse the options and set
everything up so that those rebase backends can do their work.

Note: We take an alternative approach here which is *not* to set the
environment variables via `run_command_v_opt_cd_env()` because those
variables would then be visible by processes spawned from the rebase
backends. Instead, we work hard to set them in the shell script snippet.

The next commits will handle and support all the wonderful rebase
options.

Signed-off-by: Pratik Karki <predatoramigo@gmail.com>
---
 builtin/rebase.c | 238 ++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 237 insertions(+), 1 deletion(-)

diff --git a/builtin/rebase.c b/builtin/rebase.c
index fab7fca37e..e38ea80874 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -9,6 +9,20 @@
 #include "exec-cmd.h"
 #include "argv-array.h"
 #include "dir.h"
+#include "packfile.h"
+#include "checkout.h"
+#include "refs.h"
+#include "quote.h"
+
+static GIT_PATH_FUNC(apply_dir, "rebase-apply");
+static GIT_PATH_FUNC(merge_dir, "rebase-merge");
+
+enum rebase_type {
+	REBASE_AM,
+	REBASE_MERGE,
+	REBASE_INTERACTIVE,
+	REBASE_PRESERVE_MERGES
+};
 
 static int use_builtin_rebase(void)
 {
@@ -28,8 +42,136 @@ static int use_builtin_rebase(void)
 	return ret;
 }
 
+static int apply_autostash(void)
+{
+	warning("TODO");
+	return 0;
+}
+
+struct rebase_options {
+	enum rebase_type type;
+	const char *state_dir;
+	struct commit *upstream;
+	const char *upstream_name;
+	char *head_name;
+	struct object_id orig_head;
+	struct commit *onto;
+	const char *onto_name;
+	const char *revisions;
+	const char *root;
+};
+
+static int finish_rebase(struct rebase_options *opts)
+{
+	struct strbuf dir = STRBUF_INIT;
+	const char *argv_gc_auto[] = { "gc", "--auto", NULL };
+
+	delete_ref(NULL, "REBASE_HEAD", NULL, REF_NO_DEREF);
+	apply_autostash();
+	close_all_packs(the_repository->objects);
+	/*
+	 * We ignore errors in 'gc --auto', since the
+	 * user should see them.
+	 */
+	run_command_v_opt(argv_gc_auto, RUN_GIT_CMD);
+	strbuf_addstr(&dir, opts->state_dir);
+	remove_dir_recursively(&dir, 0);
+	strbuf_release(&dir);
+
+	return 0;
+}
+
+static struct commit *peel_committish(const char *name)
+{
+	struct object *obj;
+	struct object_id oid;
+
+	if (get_oid(name, &oid))
+		return NULL;
+	obj = parse_object(&oid);
+	return (struct commit *)peel_to_type(name, 0, obj, OBJ_COMMIT);
+}
+
+static void add_var(struct strbuf *buf, const char *name, const char *value)
+{
+	strbuf_addstr(buf, name);
+	strbuf_addstr(buf, "=");
+	sq_quote_buf(buf, value);
+	strbuf_addstr(buf, "; ");
+}
+
+static int run_specific_rebase(struct rebase_options *opts)
+{
+	const char *argv[] = { NULL, NULL };
+	struct strbuf script_snippet = STRBUF_INIT;
+	int status;
+	const char *backend, *backend_func;
+
+	add_var(&script_snippet, "GIT_DIR", absolute_path(get_git_dir()));
+
+	add_var(&script_snippet, "upstream_name", opts->upstream_name);
+	add_var(&script_snippet, "upstream",
+				 oid_to_hex(&opts->upstream->object.oid));
+	add_var(&script_snippet, "head_name", opts->head_name);
+	add_var(&script_snippet, "orig_head", oid_to_hex(&opts->orig_head));
+	add_var(&script_snippet, "onto", oid_to_hex(&opts->onto->object.oid));
+	add_var(&script_snippet, "onto_name", opts->onto_name);
+	add_var(&script_snippet, "revisions", opts->revisions);
+
+	switch (opts->type) {
+	case REBASE_AM:
+		backend = "git-rebase--am";
+		backend_func = "git_rebase__am";
+		break;
+	case REBASE_INTERACTIVE:
+		backend = "git-rebase--interactive";
+		backend_func = "git_rebase__interactive";
+		break;
+	case REBASE_MERGE:
+		backend = "git-rebase--merge";
+		backend_func = "git_rebase__merge";
+		break;
+	case REBASE_PRESERVE_MERGES:
+		backend = "git-rebase--preserve-merges";
+		backend_func = "git_rebase__preserve_merges";
+		break;
+	default:
+		BUG("Unhandled rebase type %d", opts->type);
+		break;
+	}
+
+	strbuf_addf(&script_snippet,
+		    ". git-rebase--common && . %s && %s",
+		    backend, backend_func);
+	argv[0] = script_snippet.buf;
+
+	status = run_command_v_opt(argv, RUN_USING_SHELL);
+	if (status == 0)
+		finish_rebase(opts);
+	else if (status == 2) {
+		struct strbuf dir = STRBUF_INIT;
+
+		apply_autostash();
+		strbuf_addstr(&dir, opts->state_dir);
+		remove_dir_recursively(&dir, 0);
+		strbuf_release(&dir);
+		die("Nothing to do");
+	}
+
+	strbuf_release(&script_snippet);
+
+	return status ? -1 : 0;
+}
+
 int cmd_rebase(int argc, const char **argv, const char *prefix)
 {
+	struct rebase_options options = { -1 };
+	const char *branch_name;
+	int ret, flags, quiet = 0;
+	struct strbuf msg = STRBUF_INIT;
+	struct strbuf revisions = STRBUF_INIT;
+	const char *restrict_revision = NULL;
+
 	/*
 	 * NEEDSWORK: Once the builtin rebase has been tested enough
 	 * and git-legacy-rebase.sh is retired to contrib/, this preamble
@@ -52,5 +194,99 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	trace_repo_setup(prefix);
 	setup_work_tree();
 
-	die("TODO");
+	options.type = REBASE_AM;
+
+	switch (options.type) {
+	case REBASE_AM:
+		options.state_dir = apply_dir();
+		break;
+	case REBASE_MERGE:
+	case REBASE_INTERACTIVE:
+	case REBASE_PRESERVE_MERGES:
+		options.state_dir = merge_dir();
+		break;
+	}
+	if (!options.root) {
+		if (argc != 2)
+			die("TODO: handle @{upstream}");
+		else {
+			options.upstream_name = argv[1];
+			argc--;
+			argv++;
+			if (!strcmp(options.upstream_name, "-"))
+				options.upstream_name = "@{-1}";
+		}
+		options.upstream = peel_committish(options.upstream_name);
+		if (!options.upstream)
+			die(_("invalid upstream '%s'"), options.upstream_name);
+	} else
+		die("TODO: upstream for --root");
+
+	/* Make sure the branch to rebase onto is valid. */
+	if (!options.onto_name)
+		options.onto_name = options.upstream_name;
+	if (strstr(options.onto_name, "...")) {
+		die("TODO");
+	} else {
+		options.onto = peel_committish(options.onto_name);
+		if (!options.onto)
+			die(_("Does not point to a valid commit '%s'"),
+				options.onto_name);
+	}
+
+	/*
+	 * If the branch to rebase is given, that is the branch we will rebase
+	 * branch_name -- branch/commit being rebased, or
+	 * 		  HEAD (already detached)
+	 * orig_head -- commit object name of tip of the branch before rebasing
+	 * head_name -- refs/heads/<that-branch> or "detached HEAD"
+	 */
+	if (argc > 1)
+		 die("TODO: handle switch_to");
+	else {
+		/* Do not need to switch branches, we are already on it. */
+		options.head_name =
+			xstrdup_or_null(resolve_ref_unsafe("HEAD", 0, NULL,
+					 &flags));
+		if (!options.head_name)
+			die(_("No such ref: %s"), "HEAD");
+		if (flags & REF_ISSYMREF) {
+			if (!skip_prefix(options.head_name,
+					 "refs/heads/", &branch_name))
+				branch_name = options.head_name;
+
+		} else {
+			options.head_name = xstrdup("detached HEAD");
+			branch_name = "HEAD";
+		}
+		if (get_oid("HEAD", &options.orig_head))
+			die(_("Could not resolve HEAD to a revision"));
+	}
+
+	/* Detach HEAD and reset the tree */
+	if (!quiet)
+		printf("First, rewinding head to replay your work on top of it...");
+
+	strbuf_addf(&msg, "rebase: checkout %s", options.onto_name);
+	if (detach_head_to(&options.onto->object.oid, "checkout", msg.buf))
+		die(_("Could not detach HEAD"));
+	strbuf_release(&msg);
+	if (update_ref("rebase", "ORIG_HEAD", &options.orig_head, NULL, 0,
+		       UPDATE_REFS_MSG_ON_ERR) < 0)
+		die(_("Could not update ORIG_HEAD to '%s'"),
+		    oid_to_hex(&options.orig_head));
+
+	strbuf_addf(&revisions, "%s..%s",
+		!options.root ? oid_to_hex(&options.onto->object.oid) :
+		    (restrict_revision ? restrict_revision :
+			    oid_to_hex(&options.upstream->object.oid)),
+			    oid_to_hex(&options.orig_head));
+
+	options.revisions = revisions.buf;
+
+	ret = !!run_specific_rebase(&options);
+
+	strbuf_release(&revisions);
+	free(options.head_name);
+	return ret;
 }
-- 
2.18.0