branch: accept multiple upstream branches for tracking

Add a new static variant of install_branch_config() that accepts
multiple remote branch names for tracking. This will be used in an
upcoming commit that enables inheriting the tracking configuration from
a parent branch.

Currently, all callers of install_branch_config() pass only a single
remote. Make install_branch_config() a small wrapper around
install_branch_config_multiple_remotes() so that existing callers do not
need to be changed.

Signed-off-by: Josh Steadmon <steadmon@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

branch.c

@@ -49,25 +49,46 @@ static int should_setup_rebase(const char *origin)
 	return 0;
 }
 
-static const char tracking_advice[] =
+/**
-N_("\n"
+ * Install upstream tracking configuration for a branch; specifically, add
-"After fixing the error cause you may try to fix up\n"
+ * `branch.<name>.remote` and `branch.<name>.merge` entries.
-"the remote tracking information by invoking\n"
+ *
-"\"git branch --set-upstream-to=%s%s%s\".");
+ * `flag` contains integer flags for options; currently only
-
+ * BRANCH_CONFIG_VERBOSE is checked.
-int install_branch_config(int flag, const char *local, const char *origin, const char *remote)
+ *
+ * `local` is the name of the branch whose configuration we're installing.
+ *
+ * `origin` is the name of the remote owning the upstream branches. NULL means
+ * the upstream branches are local to this repo.
+ *
+ * `remotes` is a list of refs that are upstream of local
+ */
+static int install_branch_config_multiple_remotes(int flag, const char *local,
+		const char *origin, struct string_list *remotes)
 {
 	const char *shortname = NULL;
 	struct strbuf key = STRBUF_INIT;
+	struct string_list_item *item;
 	int rebasing = should_setup_rebase(origin);
 
-	if (skip_prefix(remote, "refs/heads/", &shortname)
+	if (!remotes->nr)
-	    && !strcmp(local, shortname)
+		BUG("must provide at least one remote for branch config");
-	    && !origin) {
+	if (rebasing && remotes->nr > 1)
-		warning(_("Not setting branch %s as its own upstream."),
+		die(_("cannot inherit upstream tracking configuration of "
-			local);
+		      "multiple refs when rebasing is requested"));
-		return 0;
+
-	}
+	/*
+	 * If the new branch is trying to track itself, something has gone
+	 * wrong. Warn the user and don't proceed any further.
+	 */
+	if (!origin)
+		for_each_string_list_item(item, remotes)
+			if (skip_prefix(item->string, "refs/heads/", &shortname)
+			    && !strcmp(local, shortname)) {
+				warning(_("not setting branch '%s' as its own upstream."),
+					local);
+				return 0;
+			}
 
 	strbuf_addf(&key, "branch.%s.remote", local);
 	if (git_config_set_gently(key.buf, origin ? origin : ".") < 0)
@@ -75,8 +96,17 @@ int install_branch_config(int flag, const char *local, const char *origin, const
 
 	strbuf_reset(&key);
 	strbuf_addf(&key, "branch.%s.merge", local);
-	if (git_config_set_gently(key.buf, remote) < 0)
+	/*
+	 * We want to overwrite any existing config with all the branches in
+	 * "remotes". Override any existing config, then write our branches. If
+	 * more than one is provided, use CONFIG_REGEX_NONE to preserve what
+	 * we've written so far.
+	 */
+	if (git_config_set_gently(key.buf, NULL) < 0)
 		goto out_err;
+	for_each_string_list_item(item, remotes)
+		if (git_config_set_multivar_gently(key.buf, item->string, CONFIG_REGEX_NONE, 0) < 0)
+			goto out_err;
 
 	if (rebasing) {
 		strbuf_reset(&key);
@@ -87,29 +117,40 @@ int install_branch_config(int flag, const char *local, const char *origin, const
 	strbuf_release(&key);
 
 	if (flag & BRANCH_CONFIG_VERBOSE) {
-		if (shortname) {
+		struct strbuf tmp_ref_name = STRBUF_INIT;
-			if (origin)
+		struct string_list friendly_ref_names = STRING_LIST_INIT_DUP;
-				printf_ln(rebasing ?
+
-					  _("Branch '%s' set up to track remote branch '%s' from '%s' by rebasing.") :
+		for_each_string_list_item(item, remotes) {
-					  _("Branch '%s' set up to track remote branch '%s' from '%s'."),
+			shortname = item->string;
-					  local, shortname, origin);
+			skip_prefix(shortname, "refs/heads/", &shortname);
-			else
+			if (origin) {
-				printf_ln(rebasing ?
+				strbuf_addf(&tmp_ref_name, "%s/%s",
-					  _("Branch '%s' set up to track local branch '%s' by rebasing.") :
+					    origin, shortname);
-					  _("Branch '%s' set up to track local branch '%s'."),
+				string_list_append_nodup(
-					  local, shortname);
+					&friendly_ref_names,
-		} else {
+					strbuf_detach(&tmp_ref_name, NULL));
-			if (origin)
+			} else {
-				printf_ln(rebasing ?
+				string_list_append(
-					  _("Branch '%s' set up to track remote ref '%s' by rebasing.") :
+					&friendly_ref_names, shortname);
-					  _("Branch '%s' set up to track remote ref '%s'."),
+			}
-					  local, remote);
-			else
-				printf_ln(rebasing ?
-					  _("Branch '%s' set up to track local ref '%s' by rebasing.") :
-					  _("Branch '%s' set up to track local ref '%s'."),
-					  local, remote);
 		}
+
+		if (remotes->nr == 1) {
+			/*
+			 * Rebasing is only allowed in the case of a single
+			 * upstream branch.
+			 */
+			printf_ln(rebasing ?
+				_("branch '%s' set up to track '%s' by rebasing.") :
+				_("branch '%s' set up to track '%s'."),
+				local, friendly_ref_names.items[0].string);
+		} else {
+			printf_ln(_("branch '%s' set up to track:"), local);
+			for_each_string_list_item(item, &friendly_ref_names)
+				printf_ln("  %s", item->string);
+		}
+
+		string_list_clear(&friendly_ref_names, 0);
 	}
 
 	return 0;
@@ -118,14 +159,36 @@ out_err:
 	strbuf_release(&key);
 	error(_("Unable to write upstream branch configuration"));
 
-	advise(_(tracking_advice),
+	advise(_("\nAfter fixing the error cause you may try to fix up\n"
-	       origin ? origin : "",
+		"the remote tracking information by invoking:"));
-	       origin ? "/" : "",
+	if (remotes->nr == 1)
-	       shortname ? shortname : remote);
+		advise("  git branch --set-upstream-to=%s%s%s",
+			origin ? origin : "",
+			origin ? "/" : "",
+			remotes->items[0].string);
+	else {
+		advise("  git config --add branch.\"%s\".remote %s",
+			local, origin ? origin : ".");
+		for_each_string_list_item(item, remotes)
+			advise("  git config --add branch.\"%s\".merge %s",
+				local, item->string);
+	}
 
 	return -1;
 }
 
+int install_branch_config(int flag, const char *local, const char *origin,
+		const char *remote)
+{
+	int ret;
+	struct string_list remotes = STRING_LIST_INIT_DUP;
+
+	string_list_append(&remotes, remote);
+	ret = install_branch_config_multiple_remotes(flag, local, origin, &remotes);
+	string_list_clear(&remotes, 0);
+	return ret;
+}
+
 /*
  * 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

t/t3200-branch.sh

@@ -950,15 +950,15 @@ test_expect_success 'disabled option --set-upstream fails' '
 	test_must_fail git branch --set-upstream origin/main
 '
 
-test_expect_success '--set-upstream-to notices an error to set branch as own upstream' '
+test_expect_success '--set-upstream-to notices an error to set branch as own upstream' "
 	git branch --set-upstream-to refs/heads/my13 my13 2>actual &&
 	cat >expect <<-\EOF &&
-	warning: Not setting branch my13 as its own upstream.
+	warning: not setting branch 'my13' as its own upstream.
 	EOF
 	test_expect_code 1 git config branch.my13.remote &&
 	test_expect_code 1 git config branch.my13.merge &&
 	test_cmp expect actual
-'
+"
 
 # Keep this test last, as it changes the current branch
 cat >expect <<EOF