branch: add flags and config to inherit tracking

It can be helpful when creating a new branch to use the existing
tracking configuration from the branch point. However, there is
currently not a method to automatically do so.

Teach git-{branch,checkout,switch} an "inherit" argument to the
"--track" option. When this is set, creating a new branch will cause the
tracking configuration to default to the configuration of the branch
point, if set.

For example, if branch "main" tracks "origin/main", and we run
`git checkout --track=inherit -b feature main`, then branch "feature"
will track "origin/main". Thus, `git status` will show us how far
ahead/behind we are from origin, and `git pull` will pull from origin.

This is particularly useful when creating branches across many
submodules, such as with `git submodule foreach ...` (or if running with
a patch such as [1], which we use at $job), as it avoids having to
manually set tracking info for each submodule.

Since we've added an argument to "--track", also add "--track=direct" as
another way to explicitly get the original "--track" behavior ("--track"
without an argument still works as well).

Finally, teach branch.autoSetupMerge a new "inherit" option. When this
is set, "--track=inherit" becomes the default behavior.

[1]: https://lore.kernel.org/git/[email protected]/

Signed-off-by: Josh Steadmon <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: steadmon

Documentation/config/branch.txt

@@ -7,7 +7,8 @@ branch.autoSetupMerge::
 	automatic setup is done; `true` -- automatic setup is done when the
 	starting point is a remote-tracking branch; `always` --
 	automatic setup is done when the starting point is either a
-	local branch or remote-tracking
+	local branch or remote-tracking branch; `inherit` -- if the starting point
+	has a tracking configuration, it is copied to the new
 	branch. This option defaults to true.
 
 branch.autoSetupRebase::

Documentation/git-branch.txt

@@ -16,7 +16,7 @@ SYNOPSIS
 	[--points-at <object>] [--format=<format>]
 	[(-r | --remotes) | (-a | --all)]
 	[--list] [<pattern>...]
-'git branch' [--track | --no-track] [-f] <branchname> [<start-point>]
+'git branch' [--track [direct|inherit] | --no-track] [-f] <branchname> [<start-point>]
 'git branch' (--set-upstream-to=<upstream> | -u <upstream>) [<branchname>]
 'git branch' --unset-upstream [<branchname>]
 'git branch' (-m | -M) [<oldbranch>] <newbranch>
@@ -206,24 +206,34 @@ This option is only applicable in non-verbose mode.
 	Display the full sha1s in the output listing rather than abbreviating them.
 
 -t::
---track::
+--track [inherit|direct]::
 	When creating a new branch, set up `branch.<name>.remote` and
-	`branch.<name>.merge` configuration entries to mark the
-	start-point branch as "upstream" from the new branch. This
+	`branch.<name>.merge` configuration entries to set "upstream" tracking
+	configuration for the new branch. This
 	configuration will tell git to show the relationship between the
 	two branches in `git status` and `git branch -v`. Furthermore,
 	it directs `git pull` without arguments to pull from the
 	upstream when the new branch is checked out.
 +
-This behavior is the default when the start point is a remote-tracking branch.
+The exact upstream branch is chosen depending on the optional argument:
+`--track` or `--track direct` means to use the start-point branch itself as the
+upstream; `--track inherit` means to copy the upstream configuration of the
+start-point branch.
++
+`--track direct` is the default when the start point is a remote-tracking branch.
 Set the branch.autoSetupMerge configuration variable to `false` if you
 want `git switch`, `git checkout` and `git branch` to always behave as if `--no-track`
 were given. Set it to `always` if you want this behavior when the
-start-point is either a local or remote-tracking branch.
+start-point is either a local or remote-tracking branch. Set it to
+`inherit` if you want to copy the tracking configuration from the
+branch point.
++
+See linkgit:git-pull[1] and linkgit:git-config[1] for additional discussion on
+how the `branch.<name>.remote` and `branch.<name>.merge` options are used.
 
 --no-track::
 	Do not set up "upstream" configuration, even if the
-	branch.autoSetupMerge configuration variable is true.
+	branch.autoSetupMerge configuration variable is set.
 
 --set-upstream::
 	As this option had confusing syntax, it is no longer supported.

Documentation/git-checkout.txt

@@ -156,7 +156,7 @@ of it").
 	linkgit:git-branch[1] for details.
 
 -t::
---track::
+--track [direct|inherit]::
 	When creating a new branch, set up "upstream" configuration. See
 	"--track" in linkgit:git-branch[1] for details.
 +

Documentation/git-switch.txt

@@ -152,7 +152,7 @@ should result in deletion of the path).
 	attached to a terminal, regardless of `--quiet`.
 
 -t::
---track::
+--track [direct|inherit]::
 	When creating a new branch, set up "upstream" configuration.
 	`-c` is implied. See `--track` in linkgit:git-branch[1] for
 	details.

branch.c

@@ -11,7 +11,7 @@
 
 struct tracking {
 	struct refspec_item spec;
-	char *src;
+	struct string_list *srcs;
 	const char *remote;
 	int matches;
 };
@@ -22,11 +22,11 @@ static int find_tracked_branch(struct remote *remote, void *priv)
 
 	if (!remote_find_tracking(remote, &tracking->spec)) {
 		if (++tracking->matches == 1) {
-			tracking->src = tracking->spec.src;
+			string_list_append(tracking->srcs, tracking->spec.src);
 			tracking->remote = remote->name;
 		} else {
 			free(tracking->spec.src);
-			FREE_AND_NULL(tracking->src);
+			string_list_clear(tracking->srcs, 0);
 		}
 		tracking->spec.src = NULL;
 	}
@@ -189,6 +189,34 @@ int install_branch_config(int flag, const char *local, const char *origin,
 	return ret;
 }
 
+static int inherit_tracking(struct tracking *tracking, const char *orig_ref)
+{
+	const char *bare_ref;
+	struct branch *branch;
+	int i;
+
+	bare_ref = orig_ref;
+	skip_prefix(orig_ref, "refs/heads/", &bare_ref);
+
+	branch = branch_get(bare_ref);
+	if (!branch->remote_name) {
+		warning(_("asked to inherit tracking from '%s', but no remote is set"),
+			bare_ref);
+		return -1;
+	}
+
+	if (branch->merge_nr < 1 || !branch->merge_name || !branch->merge_name[0]) {
+		warning(_("asked to inherit tracking from '%s', but no merge configuration is set"),
+			bare_ref);
+		return -1;
+	}
+
+	tracking->remote = xstrdup(branch->remote_name);
+	for (i = 0; i < branch->merge_nr; i++)
+		string_list_append(tracking->srcs, branch->merge_name[i]);
+	return 0;
+}
+
 /*
  * This is called when new_ref is branched off of orig_ref, and tries
  * to infer the settings for branch.<new_ref>.{remote,merge} from the
@@ -198,18 +226,23 @@ static void setup_tracking(const char *new_ref, const char *orig_ref,
 			   enum branch_track track, int quiet)
 {
 	struct tracking tracking;
+	struct string_list tracking_srcs = STRING_LIST_INIT_DUP;
 	int config_flags = quiet ? 0 : BRANCH_CONFIG_VERBOSE;
 
 	memset(&tracking, 0, sizeof(tracking));
 	tracking.spec.dst = (char *)orig_ref;
-	if (for_each_remote(find_tracked_branch, &tracking))
+	tracking.srcs = &tracking_srcs;
+	if (track != BRANCH_TRACK_INHERIT)
+		for_each_remote(find_tracked_branch, &tracking);
+	else if (inherit_tracking(&tracking, orig_ref))
 		return;
 
 	if (!tracking.matches)
 		switch (track) {
 		case BRANCH_TRACK_ALWAYS:
 		case BRANCH_TRACK_EXPLICIT:
 		case BRANCH_TRACK_OVERRIDE:
+		case BRANCH_TRACK_INHERIT:
 			break;
 		default:
 			return;
@@ -219,11 +252,13 @@ static void setup_tracking(const char *new_ref, const char *orig_ref,
 		die(_("Not tracking: ambiguous information for ref %s"),
 		    orig_ref);
 
-	if (install_branch_config(config_flags, new_ref, tracking.remote,
-			      tracking.src ? tracking.src : orig_ref) < 0)
+	if (tracking.srcs->nr < 1)
+		string_list_append(tracking.srcs, orig_ref);
+	if (install_branch_config_multiple_remotes(config_flags, new_ref,
+				tracking.remote, tracking.srcs) < 0)
 		exit(-1);
 
-	free(tracking.src);
+	string_list_clear(tracking.srcs, 0);
 }
 
 int read_branch_desc(struct strbuf *buf, const char *branch_name)

branch.h

@@ -10,7 +10,8 @@ enum branch_track {
 	BRANCH_TRACK_REMOTE,
 	BRANCH_TRACK_ALWAYS,
 	BRANCH_TRACK_EXPLICIT,
-	BRANCH_TRACK_OVERRIDE
+	BRANCH_TRACK_OVERRIDE,
+	BRANCH_TRACK_INHERIT,
 };
 
 extern enum branch_track git_branch_track;

builtin/branch.c

@@ -632,8 +632,10 @@ int cmd_branch(int argc, const char **argv, const char *prefix)
 		OPT__VERBOSE(&filter.verbose,
 			N_("show hash and subject, give twice for upstream branch")),
 		OPT__QUIET(&quiet, N_("suppress informational messages")),
-		OPT_SET_INT('t', "track",  &track, N_("set up tracking mode (see git-pull(1))"),
-			BRANCH_TRACK_EXPLICIT),
+		OPT_CALLBACK_F('t', "track",  &track, "direct|inherit",
+			N_("set branch tracking configuration"),
+			PARSE_OPT_OPTARG | PARSE_OPT_LITERAL_ARGHELP,
+			parse_opt_tracking_mode),
 		OPT_SET_INT_F(0, "set-upstream", &track, N_("do not use"),
 			BRANCH_TRACK_OVERRIDE, PARSE_OPT_HIDDEN),
 		OPT_STRING('u', "set-upstream-to", &new_upstream, N_("upstream"), N_("change the upstream info")),

builtin/checkout.c

@@ -1530,8 +1530,10 @@ static struct option *add_common_switch_branch_options(
 {
 	struct option options[] = {
 		OPT_BOOL('d', "detach", &opts->force_detach, N_("detach HEAD at named commit")),
-		OPT_SET_INT('t', "track",  &opts->track, N_("set upstream info for new branch"),
-			BRANCH_TRACK_EXPLICIT),
+		OPT_CALLBACK_F('t', "track",  &opts->track, "direct|inherit",
+			N_("set up tracking mode (see git-pull(1))"),
+			PARSE_OPT_OPTARG | PARSE_OPT_LITERAL_ARGHELP,
+			parse_opt_tracking_mode),
 		OPT__FORCE(&opts->force, N_("force checkout (throw away local modifications)"),
 			   PARSE_OPT_NOCOMPLETE),
 		OPT_STRING(0, "orphan", &opts->new_orphan_branch, N_("new-branch"), N_("new unparented branch")),

config.c

@@ -1559,6 +1559,9 @@ static int git_default_branch_config(const char *var, const char *value)
 		if (value && !strcasecmp(value, "always")) {
 			git_branch_track = BRANCH_TRACK_ALWAYS;
 			return 0;
+		} else if (value && !strcmp(value, "inherit")) {
+			git_branch_track = BRANCH_TRACK_INHERIT;
+			return 0;
 		}
 		git_branch_track = git_config_bool(var, value);
 		return 0;

parse-options-cb.c

@@ -1,5 +1,6 @@
 #include "git-compat-util.h"
 #include "parse-options.h"
+#include "branch.h"
 #include "cache.h"
 #include "commit.h"
 #include "color.h"
@@ -293,3 +294,18 @@ int parse_opt_passthru_argv(const struct option *opt, const char *arg, int unset
 
 	return 0;
 }
+
+int parse_opt_tracking_mode(const struct option *opt, const char *arg, int unset)
+{
+	if (unset)
+		*(enum branch_track *)opt->value = BRANCH_TRACK_NEVER;
+	else if (!arg || !strcmp(arg, "direct"))
+		*(enum branch_track *)opt->value = BRANCH_TRACK_EXPLICIT;
+	else if (!strcmp(arg, "inherit"))
+		*(enum branch_track *)opt->value = BRANCH_TRACK_INHERIT;
+	else
+		return error(_("option `%s' expects \"%s\" or \"%s\""),
+			     "--track", "direct", "inherit");
+
+	return 0;
+}