[PATCH v2 1/2] branch: suggest <remote>/<branch> on upstream slip

["Harald Nordgren via GitGitGadget" <gitgitgadget@gmail.com>]

From: Harald Nordgren <haraldnordgren@gmail.com>

When setting the upstream of the current branch to the 'main' branch
of the remote 'origin', i.e.,

    $ git branch --set-upstream-to origin/main

it is easy to mistakenly write

    $ git branch --set-upstream-to origin main

That is parsed as a request to set the upstream of the local branch
'main' to 'origin'. When 'main' does not exist, the command dies
with:

    fatal: branch 'main' does not exist

pointing at a branch the user never meant to name.

When the operated-on branch is missing and '<remote>/<branch>' names
a real remote-tracking ref, suggest the intended form:

    $ git branch --set-upstream-to=origin/main

The suggestion is gated on '<remote>/<branch>' existing so it only
appears when a slipped slash is the likely explanation.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 builtin/branch.c  | 26 ++++++++++++++++++++++++++
 t/t3200-branch.sh | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 64 insertions(+)

diff --git a/builtin/branch.c b/builtin/branch.c
index 1572a4f9ef..cefc4519a7 100644
--- a/builtin/branch.c
+++ b/builtin/branch.c
@@ -706,6 +706,29 @@ static int edit_branch_description(const char *branch_name)
 	return 0;
 }
 
+static void die_if_upstream_looks_like_remote(const char *new_upstream, const char *branch_name)
+{
+	struct strbuf remote_ref = STRBUF_INIT;
+	int code;
+
+	if (strchr(new_upstream, '/') ||
+	    !remote_is_configured(remote_get(new_upstream), 0))
+		return;
+
+	strbuf_addf(&remote_ref, "refs/remotes/%s/%s", new_upstream, branch_name);
+	if (!refs_ref_exists(get_main_ref_store(the_repository), remote_ref.buf)) {
+		strbuf_release(&remote_ref);
+		return;
+	}
+
+	code = die_message(_("--set-upstream-to takes a single <remote>/<branch> argument"));
+	advise_if_enabled(ADVICE_SET_UPSTREAM_FAILURE,
+			  _("Did you mean to use: git branch --set-upstream-to=%s/%s?"),
+			  new_upstream, branch_name);
+	strbuf_release(&remote_ref);
+	exit(code);
+}
+
 int cmd_branch(int argc,
 	       const char **argv,
 	       const char *prefix,
@@ -957,6 +980,9 @@ int cmd_branch(int argc,
 		if (!refs_ref_exists(get_main_ref_store(the_repository), branch->refname)) {
 			if (!argc || branch_checked_out(branch->refname))
 				die(_("no commit on branch '%s' yet"), branch->name);
+			if (argc == 1 &&
+			    advice_enabled(ADVICE_SET_UPSTREAM_FAILURE))
+				die_if_upstream_looks_like_remote(new_upstream, argv[0]);
 			die(_("branch '%s' does not exist"), branch->name);
 		}
 
diff --git a/t/t3200-branch.sh b/t/t3200-branch.sh
index e7829c2c4b..e2682a83a0 100755
--- a/t/t3200-branch.sh
+++ b/t/t3200-branch.sh
@@ -1022,6 +1022,44 @@ test_expect_success '--set-upstream-to fails on a missing dst branch' '
 	test_cmp expect err
 '
 
+test_expect_success '--set-upstream-to suggests <remote>/<branch> on slip' '
+	test_when_finished "git remote remove slip-remote" &&
+	git remote add slip-remote . &&
+	git update-ref refs/remotes/slip-remote/slip-feature HEAD &&
+	test_must_fail git branch --set-upstream-to slip-remote slip-feature 2>err &&
+	test_grep "takes a single <remote>/<branch> argument" err &&
+	test_grep "hint: Did you mean to use: git branch --set-upstream-to=slip-remote/slip-feature?" err &&
+	test_must_fail git -c advice.setUpstreamFailure=false \
+		branch --set-upstream-to slip-remote slip-feature 2>err &&
+	test_grep ! "Did you mean" err
+'
+
+test_expect_success '--set-upstream-to does not suggest when no matching remote ref' '
+	test_when_finished "git remote remove slip-remote" &&
+	git remote add slip-remote . &&
+	test_must_fail git branch --set-upstream-to slip-remote no-such-branch 2>err &&
+	test_grep "branch ${SQ}no-such-branch${SQ} does not exist" err &&
+	test_grep ! "Did you mean" err
+'
+
+test_expect_success '--set-upstream-to to a local branch is not mistaken for a slip' '
+	git branch slip-local-upstream &&
+	git branch slip-local-target &&
+	git branch --set-upstream-to=slip-local-upstream slip-local-target 2>err &&
+	test_grep ! "Did you mean" err &&
+	echo refs/heads/slip-local-upstream >expect &&
+	git config branch.slip-local-target.merge >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success '--set-upstream-to slip suggestion keeps a slashed branch name' '
+	test_when_finished "git remote remove slip-remote" &&
+	git remote add slip-remote . &&
+	git update-ref refs/remotes/slip-remote/slip/feature HEAD &&
+	test_must_fail git branch --set-upstream-to slip-remote slip/feature 2>err &&
+	test_grep "hint: Did you mean to use: git branch --set-upstream-to=slip-remote/slip/feature?" err
+'
+
 test_expect_success '--set-upstream-to fails on a missing src branch' '
 	test_must_fail git branch --set-upstream-to does-not-exist main 2>err &&
 	test_grep "the requested upstream branch '"'"'does-not-exist'"'"' does not exist" err
-- 
gitgitgadget