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, 29 insertions, 0 deletions

diff --git a/branch.h b/branch.h
index 509cfcc..04df2aa5 100644
--- a/branch.h
+++ b/branch.h
@@ -72,6 +72,35 @@ void create_branch(struct repository *r,
 		   int dry_run);
 
 /*
+ * Creates a new branch in a repository and its submodules (and its
+ * submodules, recursively). The parameters are mostly analogous to
+ * those of create_branch() except for start_name, which is represented
+ * by two different parameters:
+ *
+ * - start_commitish is the commit-ish, in repository r, that determines
+ *   which commits the branches will point to. The superproject branch
+ *   will point to the commit of start_commitish and the submodule
+ *   branches will point to the gitlink commit oids in start_commitish's
+ *   tree.
+ *
+ * - tracking_name is the name of the ref, in repository r, that will be
+ *   used to set up tracking information. This value is propagated to
+ *   all submodules, which will evaluate the ref using their own ref
+ *   stores. If NULL, this defaults to start_commitish.
+ *
+ * When this function is called on the superproject, start_commitish
+ * can be any user-provided ref and tracking_name can be NULL (similar
+ * to create_branches()). But when recursing through submodules,
+ * start_commitish is the plain gitlink commit oid. Since the oid cannot
+ * be used for tracking information, tracking_name is propagated and
+ * used for tracking instead.
+ */
+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);
+/*
  * Check if 'name' can be a valid name for a branch; die otherwise.
  * Return 1 if the named branch already exists; return 0 otherwise.
  * Fill ref with the full refname for the branch.