status: show comparison with push remote tracking branch

"git status" on a branch that follows a remote branch compares
commits on the current branch and the remote-tracking branch it
builds upon, to show "ahead", "behind", or "diverged" status.

When working on a feature branch that tracks a remote feature branch,
but you also want to track progress relative to the push destination
tracking branch (which may differ from the upstream branch), git status
now shows an additional comparison.

When the upstream tracking branch differs from the push destination
tracking branch, git status shows both the comparison with the upstream
tracking branch (as before) and an additional comparison with the push
destination tracking branch. The push branch comparison appears on a
separate line after the upstream branch status, using the same format.

Example output when tracking origin/main but push destination is
origin/feature:
    On branch feature
    Your branch and 'origin/main' have diverged,
    and have 3 and 1 different commits each, respectively.
      (use "git pull" if you want to integrate the remote branch with yours)

    Your branch is ahead of 'origin/feature' by 1 commit.
      (use "git push" to publish your local commits)

The comparison is only shown when the push destination tracking branch
differs from the upstream tracking branch, even if they are on the same
remote.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: HaraldNordgren

remote.c

@@ -29,6 +29,11 @@
 
 enum map_direction { FROM_SRC, FROM_DST };
 
+enum {
+	BRANCH_MODE_PULL = (1 << 0),
+	BRANCH_MODE_PUSH = (1 << 1),
+};
+
 struct counted_string {
 	size_t len;
 	const char *s;
@@ -2237,13 +2242,75 @@ int stat_tracking_info(struct branch *branch, int *num_ours, int *num_theirs,
 	return stat_branch_pair(branch->refname, base, num_ours, num_theirs, abf);
 }
 
+static char *get_remote_push_branch(struct branch *branch, char **full_ref_out)
+{
+	struct remote *remote;
+	const char *push_remote;
+	char *push_dst = NULL;
+	char *tracking_ref;
+	const char *resolved;
+	char *ret;
+
+	if (!branch)
+		return NULL;
+
+	push_remote = pushremote_for_branch(branch, NULL);
+	if (!push_remote)
+		return NULL;
+
+	remote = remotes_remote_get(the_repository, push_remote);
+	if (!remote)
+		return NULL;
+
+	push_dst = remote_ref_for_branch(branch, 1);
+	if (!push_dst) {
+		if (remote->push.nr)
+			return NULL;
+		push_dst = xstrdup(branch->refname);
+	}
+
+	tracking_ref = (char *)tracking_for_push_dest(remote, push_dst, NULL);
+	free(push_dst);
+
+	if (!tracking_ref)
+		return NULL;
+
+	resolved = refs_resolve_ref_unsafe(
+		get_main_ref_store(the_repository),
+		tracking_ref,
+		RESOLVE_REF_READING,
+		NULL, NULL);
+
+	if (!resolved) {
+		free(tracking_ref);
+		return NULL;
+	}
+
+	if (full_ref_out)
+		*full_ref_out = xstrdup(resolved);
+
+	ret = refs_shorten_unambiguous_ref(
+		get_main_ref_store(the_repository), resolved, 0);
+	free(tracking_ref);
+	return ret;
+}
+
 static void format_branch_comparison(struct strbuf *sb,
 				     bool up_to_date,
 				     int ours, int theirs,
 				     const char *branch_name,
 				     enum ahead_behind_flags abf,
+				     unsigned flags,
 				     bool show_divergence_advice)
 {
+	bool want_push_advice = (flags & BRANCH_MODE_PUSH) &&
+		advice_enabled(ADVICE_STATUS_HINTS);
+	bool want_pull_advice = (flags & BRANCH_MODE_PULL) &&
+		advice_enabled(ADVICE_STATUS_HINTS);
+	bool want_divergence_advice = (flags & BRANCH_MODE_PULL) &&
+		show_divergence_advice &&
+		advice_enabled(ADVICE_STATUS_HINTS);
+
 	if (up_to_date) {
 		strbuf_addf(sb,
 			_("Your branch is up to date with '%s'.\n"),
@@ -2252,7 +2319,7 @@ static void format_branch_comparison(struct strbuf *sb,
 		strbuf_addf(sb,
 			    _("Your branch and '%s' refer to different commits.\n"),
 			    branch_name);
-		if (advice_enabled(ADVICE_STATUS_HINTS))
+		if (want_push_advice)
 			strbuf_addf(sb, _("  (use \"%s\" for details)\n"),
 				    "git status --ahead-behind");
 	} else if (!theirs) {
@@ -2261,7 +2328,7 @@ static void format_branch_comparison(struct strbuf *sb,
 			   "Your branch is ahead of '%s' by %d commits.\n",
 			   ours),
 			branch_name, ours);
-		if (advice_enabled(ADVICE_STATUS_HINTS))
+		if (want_push_advice)
 			strbuf_addstr(sb,
 				_("  (use \"git push\" to publish your local commits)\n"));
 	} else if (!ours) {
@@ -2272,7 +2339,7 @@ static void format_branch_comparison(struct strbuf *sb,
 			       "and can be fast-forwarded.\n",
 			   theirs),
 			branch_name, theirs);
-		if (advice_enabled(ADVICE_STATUS_HINTS))
+		if (want_pull_advice)
 			strbuf_addstr(sb,
 				_("  (use \"git pull\" to update your local branch)\n"));
 	} else {
@@ -2285,8 +2352,7 @@ static void format_branch_comparison(struct strbuf *sb,
 			       "respectively.\n",
 			   ours + theirs),
 			branch_name, ours, theirs);
-		if (show_divergence_advice &&
-		    advice_enabled(ADVICE_STATUS_HINTS))
+		if (want_divergence_advice)
 			strbuf_addstr(sb,
 				_("  (use \"git pull\" if you want to integrate the remote branch with yours)\n"));
 	}
@@ -2303,6 +2369,11 @@ int format_tracking_info(struct branch *branch, struct strbuf *sb,
 	const char *full_base;
 	char *base;
 	int upstream_is_gone = 0;
+	unsigned base_branch_modes = BRANCH_MODE_PULL | BRANCH_MODE_PUSH;
+	int push_ours, push_theirs, push_cmp_fetch;
+	char *full_push = NULL;
+	char *push = NULL;
+	unsigned push_branch_modes = 0;
 
 	cmp_fetch = stat_tracking_info(branch, &ours, &theirs, &full_base, 0, abf);
 	if (cmp_fetch < 0) {
@@ -2314,6 +2385,16 @@ int format_tracking_info(struct branch *branch, struct strbuf *sb,
 	base = refs_shorten_unambiguous_ref(get_main_ref_store(the_repository),
 					    full_base, 0);
 
+	push = get_remote_push_branch(branch, &full_push);
+	if (push && strcmp(base, push)) {
+		push_cmp_fetch = stat_branch_pair(branch->refname, full_push,
+					   &push_ours, &push_theirs, abf);
+		if (push_cmp_fetch >= 0) {
+			base_branch_modes = BRANCH_MODE_PULL;
+			push_branch_modes = BRANCH_MODE_PUSH;
+		}
+	}
+
 	if (upstream_is_gone) {
 		strbuf_addf(sb,
 			_("Your branch is based on '%s', but the upstream is gone.\n"),
@@ -2322,10 +2403,19 @@ int format_tracking_info(struct branch *branch, struct strbuf *sb,
 			strbuf_addstr(sb,
 				_("  (use \"git branch --unset-upstream\" to fixup)\n"));
 	} else {
-		format_branch_comparison(sb, !cmp_fetch, ours, theirs, base, abf, show_divergence_advice);
+		format_branch_comparison(sb, !cmp_fetch, ours, theirs, base, abf,
+					 base_branch_modes, show_divergence_advice);
+	}
+
+	if (push_branch_modes & BRANCH_MODE_PUSH) {
+		strbuf_addstr(sb, "\n");
+		format_branch_comparison(sb, !push_cmp_fetch, push_ours, push_theirs, push, abf,
+					 push_branch_modes, show_divergence_advice);
 	}
 
 	free(base);
+	free(full_push);
+	free(push);
 	return 1;
 }