t5601: exercise clones with "includeIf.*.onbranch"

It was reported that git-clone(1) started to fail in Git v2.44 when
cloning via HTTPS when the config contains an "includeIf.*.onbranch"
condition:

    $ git clone https://example.com/repo.git
    Cloning into 'repo'...
    BUG: refs.c:2083: reference backend is unknown
    error: git-remote-https died of signal 6

This regression was bisected to 0fcc285 (refs: refactor logic to look
up storage backends, 2023-12-29). This commit tightens the logic to look
up ref backends such that we now die when the backend has not yet been
detected by reading the gitconfig.

Now on its own, this commit wouldn't have caused the failure. But in
18c9cb7 (builtin/clone: create the refdb with the correct object
format, 2023-12-12) we have also changed how git-clone(1) initializes
the refdb such that it happens after the remote helper is spawned, which
is required so that we can first learn about the object format used by
the remote repository before initializing the refdb. Starting with this
change, the remote helper will be unable to detect the repository right
from the start and thus have an unconfigured ref backend. Consequently,
when we try to resolve the "includeIf.*.onbranch" condition, we will now
fail to look up the refdb and die.

This regression has already been fixed via 199f44c (builtin/clone:
allow remote helpers to detect repo, 2024-02-27), where we now
pre-initialize a partial refdb so that the remote helper can detect the
repository right from the start. But it's clear that we're lacking test
coverage of this functionality.

Add a test to avoid regressing in the future. Note that this test stops
short of defining the desired behaviour for the "onbranch" condition
during a clone. It's not quite clear how exactly it should behave, so
this is a leftover bit for the future.

Reported-by: Angelo Dureghello <angelo@kernel-space.org>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5601-clone.sh

@@ -776,6 +776,18 @@ test_expect_success 'batch missing blob request does not inadvertently try to fe
 . "$TEST_DIRECTORY"/lib-httpd.sh
 start_httpd
 
+test_expect_success 'clone with includeIf' '
+	test_when_finished "rm -rf repo \"$HTTPD_DOCUMENT_ROOT_PATH/repo.git\"" &&
+	git clone --bare --no-local src "$HTTPD_DOCUMENT_ROOT_PATH/repo.git" &&
+
+	test_when_finished "rm \"$HOME\"/.gitconfig" &&
+	cat >"$HOME"/.gitconfig <<-EOF &&
+	[includeIf "onbranch:something"]
+		path = /does/not/exist.inc
+	EOF
+	git clone $HTTPD_URL/smart/repo.git repo
+'
+
 test_expect_success 'partial clone using HTTP' '
 	partial_clone "$HTTPD_DOCUMENT_ROOT_PATH/server" "$HTTPD_URL/smart/server"
 '