branch: add --recurse-submodules option for branch creation

To improve the submodules UX, we would like to teach Git to handle
branches in submodules. Start this process by teaching "git branch" the
--recurse-submodules option so that "git branch --recurse-submodules
topic" will create the `topic` branch in the superproject and its
submodules.

Although this commit does not introduce breaking changes, it does not
work well with existing --recurse-submodules commands because "git
branch --recurse-submodules" writes to the submodule ref store, but most
commands only consider the superproject gitlink and ignore the submodule
ref store. For example, "git checkout --recurse-submodules" will check
out the commits in the superproject gitlinks (and put the submodules in
detached HEAD) instead of checking out the submodule branches.

Because of this, this commit introduces a new configuration value,
`submodule.propagateBranches`. The plan is for Git commands to
prioritize submodule ref store information over superproject gitlinks if
this value is true. Because "git branch --recurse-submodules" writes to
submodule ref stores, for the sake of clarity, it will not function
unless this configuration value is set.

This commit also includes changes that support working with submodules
from a superproject commit because "branch --recurse-submodules" (and
future commands) need to read .gitmodules and gitlinks from the
superproject commit, but submodules are typically read from the
filesystem's .gitmodules and the index's gitlinks. These changes are:

* add a submodules_of_tree() helper that gives the relevant
  information of an in-tree submodule (e.g. path and oid) and
  initializes the repository
* add is_tree_submodule_active() by adding a treeish_name parameter to
  is_submodule_active()
* add the "submoduleNotUpdated" advice to advise users to update the
  submodules in their trees

Incidentally, fix an incorrect usage string that combined the 'list'
usage of git branch (-l) with the 'create' usage; this string has been
incorrect since its inception, a8dfd5eac4 (Make builtin-branch.c use
parse_options., 2007-10-07).

Helped-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Glen Choo <chooglen@google.com>
Reviewed-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 141 insertions, 0 deletions

diff --git a/branch.c b/branch.c
index 02d46a6..70026b3 100644
--- a/branch.c
+++ b/branch.c
@@ -8,6 +8,8 @@
 #include "sequencer.h"
 #include "commit.h"
 #include "worktree.h"
+#include "submodule-config.h"
+#include "run-command.h"
 
 struct tracking {
 	struct refspec_item spec;
@@ -483,6 +485,145 @@ void dwim_and_setup_tracking(struct repository *r, const char *new_ref,
 	setup_tracking(new_ref, real_orig_ref, track, quiet);
 }
 
+/**
+ * Creates a branch in a submodule by calling
+ * create_branches_recursively() in a child process. The child process
+ * is necessary because install_branch_config_multiple_remotes() (which
+ * is called by setup_tracking()) does not support writing configs to
+ * submodules.
+ */
+static int submodule_create_branch(struct repository *r,
+				   const struct submodule *submodule,
+				   const char *name, const char *start_oid,
+				   const char *tracking_name, int force,
+				   int reflog, int quiet,
+				   enum branch_track track, int dry_run)
+{
+	int ret = 0;
+	struct child_process child = CHILD_PROCESS_INIT;
+	struct strbuf child_err = STRBUF_INIT;
+	struct strbuf out_buf = STRBUF_INIT;
+	char *out_prefix = xstrfmt("submodule '%s': ", submodule->name);
+	child.git_cmd = 1;
+	child.err = -1;
+	child.stdout_to_stderr = 1;
+
+	prepare_other_repo_env(&child.env_array, r->gitdir);
+	/*
+	 * submodule_create_branch() is indirectly invoked by "git
+	 * branch", but we cannot invoke "git branch" in the child
+	 * process. "git branch" accepts a branch name and start point,
+	 * where the start point is assumed to provide both the OID
+	 * (start_oid) and the branch to use for tracking
+	 * (tracking_name). But when recursing through submodules,
+	 * start_oid and tracking name need to be specified separately
+	 * (see create_branches_recursively()).
+	 */
+	strvec_pushl(&child.args, "submodule--helper", "create-branch", NULL);
+	if (dry_run)
+		strvec_push(&child.args, "--dry-run");
+	if (force)
+		strvec_push(&child.args, "--force");
+	if (quiet)
+		strvec_push(&child.args, "--quiet");
+	if (reflog)
+		strvec_push(&child.args, "--create-reflog");
+	if (track == BRANCH_TRACK_ALWAYS || track == BRANCH_TRACK_EXPLICIT)
+		strvec_push(&child.args, "--track");
+
+	strvec_pushl(&child.args, name, start_oid, tracking_name, NULL);
+
+	if ((ret = start_command(&child)))
+		return ret;
+	ret = finish_command(&child);
+	strbuf_read(&child_err, child.err, 0);
+	strbuf_add_lines(&out_buf, out_prefix, child_err.buf, child_err.len);
+
+	if (ret)
+		fprintf(stderr, "%s", out_buf.buf);
+	else
+		printf("%s", out_buf.buf);
+
+	strbuf_release(&child_err);
+	strbuf_release(&out_buf);
+	return ret;
+}
+
+void create_branches_recursively(struct repository *r, const char *name,
+				 const char *start_commitish,
+				 const char *tracking_name, int force,
+				 int reflog, int quiet, enum branch_track track,
+				 int dry_run)
+{
+	int i = 0;
+	char *branch_point = NULL;
+	struct object_id super_oid;
+	struct submodule_entry_list submodule_entry_list;
+
+	/* Perform dwim on start_commitish to get super_oid and branch_point. */
+	dwim_branch_start(r, start_commitish, BRANCH_TRACK_NEVER,
+			  &branch_point, &super_oid);
+
+	/*
+	 * If we were not given an explicit name to track, then assume we are at
+	 * the top level and, just like the non-recursive case, the tracking
+	 * name is the branch point.
+	 */
+	if (!tracking_name)
+		tracking_name = branch_point;
+
+	submodules_of_tree(r, &super_oid, &submodule_entry_list);
+	/*
+	 * Before creating any branches, first check that the branch can
+	 * be created in every submodule.
+	 */
+	for (i = 0; i < submodule_entry_list.entry_nr; i++) {
+		if (submodule_entry_list.entries[i].repo == NULL) {
+			if (advice_enabled(ADVICE_SUBMODULES_NOT_UPDATED))
+				advise(_("You may try updating the submodules using 'git checkout %s && git submodule update --init'"),
+				       start_commitish);
+			die(_("submodule '%s': unable to find submodule"),
+			    submodule_entry_list.entries[i].submodule->name);
+		}
+
+		if (submodule_create_branch(
+			    submodule_entry_list.entries[i].repo,
+			    submodule_entry_list.entries[i].submodule, name,
+			    oid_to_hex(&submodule_entry_list.entries[i]
+						.name_entry->oid),
+			    tracking_name, force, reflog, quiet, track, 1))
+			die(_("submodule '%s': cannot create branch '%s'"),
+			    submodule_entry_list.entries[i].submodule->name,
+			    name);
+	}
+
+	create_branch(the_repository, name, start_commitish, force, 0, reflog, quiet,
+		      BRANCH_TRACK_NEVER, dry_run);
+	if (dry_run)
+		return;
+	/*
+	 * NEEDSWORK If tracking was set up in the superproject but not the
+	 * submodule, users might expect "git branch --recurse-submodules" to
+	 * fail or give a warning, but this is not yet implemented because it is
+	 * tedious to determine whether or not tracking was set up in the
+	 * superproject.
+	 */
+	setup_tracking(name, tracking_name, track, quiet);
+
+	for (i = 0; i < submodule_entry_list.entry_nr; i++) {
+		if (submodule_create_branch(
+			    submodule_entry_list.entries[i].repo,
+			    submodule_entry_list.entries[i].submodule, name,
+			    oid_to_hex(&submodule_entry_list.entries[i]
+						.name_entry->oid),
+			    tracking_name, force, reflog, quiet, track, 0))
+			die(_("submodule '%s': cannot create branch '%s'"),
+			    submodule_entry_list.entries[i].submodule->name,
+			    name);
+		repo_clear(submodule_entry_list.entries[i].repo);
+	}
+}
+
 void remove_merge_branch_state(struct repository *r)
 {
 	unlink(git_path_merge_head(r));