[PATCH v7 1/3] branch: accept multiple upstream branches for tracking

[Josh Steadmon <steadmon@google.com>]

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>
---
 branch.c          | 140 +++++++++++++++++++++++++++++++++-------------
 t/t3200-branch.sh |   6 +-
 2 files changed, 104 insertions(+), 42 deletions(-)

diff --git a/branch.c b/branch.c
index 7a88a4861e..9e57c54848 100644
--- a/branch.c
+++ b/branch.c
@@ -49,25 +49,42 @@ static int should_setup_rebase(const char *origin)
 	return 0;
 }
 
-static const char tracking_advice[] =
-N_("\n"
-"After fixing the error cause you may try to fix up\n"
-"the remote tracking information by invoking\n"
-"\"git branch --set-upstream-to=%s%s%s\".");
-
-int install_branch_config(int flag, const char *local, const char *origin, const char *remote)
+/**
+ * Install upstream tracking configuration for a branch; specifically, add
+ * `branch.<name>.remote` and `branch.<name>.merge` entries.
+ *
+ * `flag` contains integer flags for options; currently only
+ * BRANCH_CONFIG_VERBOSE is checked.
+ *
+ * `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)
-	    && !strcmp(local, shortname)
-	    && !origin) {
-		warning(_("Not setting branch %s as its own upstream."),
-			local);
-		return 0;
-	}
+	if (!remotes->nr)
+		BUG("must provide at least one remote for branch config");
+	if (rebasing && remotes->nr > 1)
+		die(_("cannot inherit upstream tracking configuration of "
+		      "multiple refs when rebasing is requested"));
+
+	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 +92,17 @@ 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 +113,43 @@ int install_branch_config(int flag, const char *local, const char *origin, const
 	strbuf_release(&key);
 
 	if (flag & BRANCH_CONFIG_VERBOSE) {
-		if (shortname) {
+		const char *name;
+		struct strbuf ref_string = STRBUF_INIT;
+
+		for_each_string_list_item(item, remotes) {
+			name = item->string;
+			skip_prefix(name, "refs/heads/", &name);
+			strbuf_addf(&ref_string, "  %s\n", name);
+		}
+
+		if (remotes->nr == 1) {
+			struct strbuf refname = STRBUF_INIT;
+
 			if (origin)
-				printf_ln(rebasing ?
-					  _("Branch '%s' set up to track remote branch '%s' from '%s' by rebasing.") :
-					  _("Branch '%s' set up to track remote branch '%s' from '%s'."),
-					  local, shortname, origin);
-			else
-				printf_ln(rebasing ?
-					  _("Branch '%s' set up to track local branch '%s' by rebasing.") :
-					  _("Branch '%s' set up to track local branch '%s'."),
-					  local, shortname);
+				strbuf_addf(&refname, "%s/", origin);
+			skip_prefix(remotes->items[0].string, "refs/heads/", &name);
+			strbuf_addstr(&refname, name);
+
+			/*
+			 * 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, refname.buf);
+
+			strbuf_release(&refname);
+		} else if (origin) {
+			printf_ln(_("branch '%s' set up to track from '%s':"),
+				local, origin);
+			printf("%s", ref_string.buf);
 		} else {
-			if (origin)
-				printf_ln(rebasing ?
-					  _("Branch '%s' set up to track remote ref '%s' by rebasing.") :
-					  _("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);
+			printf_ln(_("branch '%s' set up to track:"), local);
+			printf("%s", ref_string.buf);
 		}
+
+		strbuf_release(&ref_string);
 	}
 
 	return 0;
@@ -118,14 +158,36 @@ int install_branch_config(int flag, const char *local, const char *origin, const
 	strbuf_release(&key);
 	error(_("Unable to write upstream branch configuration"));
 
-	advise(_(tracking_advice),
-	       origin ? origin : "",
-	       origin ? "/" : "",
-	       shortname ? shortname : remote);
+	advise(_("\nAfter fixing the error cause you may try to fix up\n"
+		"the remote tracking information by invoking:"));
+	if (remotes->nr == 1)
+		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
diff --git a/t/t3200-branch.sh b/t/t3200-branch.sh
index cc4b10236e..4b0ef35913 100755
--- a/t/t3200-branch.sh
+++ b/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
-- 
2.34.1.173.g76aa8bc2d0-goog