t/t5400: demonstrate breakage caused by informational message from prune

When receive-pack triggers 'git gc --auto' and 'git prune' is called to
remove a stale temporary object, 'git prune' prints an informational
message to stdout about the file that it will remove.  Since this message
is written to stdout, it is sent back over the transport channel to the git
client which tries to interpret it as part of the pack protocol and then
promptly terminates with a complaint about a protocol error.

Introduce a test which exercises the auto-gc functionality of receive-pack
and demonstrates this breakage.

Signed-off-by: Brandon Casey <drafnel@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: drafnel

t/t5400-send-pack.sh

@@ -145,6 +145,41 @@ test_expect_success 'push --all excludes remote-tracking hierarchy' '
 	)
 '
 
+test_expect_failure 'receive-pack runs auto-gc in remote repo' '
+	rm -rf parent child &&
+	git init parent &&
+	(
+	    # Setup a repo with 2 packs
+	    cd parent &&
+	    echo "Some text" >file.txt &&
+	    git add . &&
+	    git commit -m "Initial commit" &&
+	    git repack -adl &&
+	    echo "Some more text" >>file.txt &&
+	    git commit -a -m "Second commit" &&
+	    git repack
+	) &&
+	cp -a parent child &&
+	(
+	    # Set the child to auto-pack if more than one pack exists
+	    cd child &&
+	    git config gc.autopacklimit 1 &&
+	    git branch test_auto_gc &&
+	    # And create a file that follows the temporary object naming
+	    # convention for the auto-gc to remove
+	    : >.git/objects/tmp_test_object &&
+	    test-chmtime =-1209601 .git/objects/tmp_test_object
+	) &&
+	(
+	    cd parent &&
+	    echo "Even more text" >>file.txt &&
+	    git commit -a -m "Third commit" &&
+	    git send-pack ../child HEAD:refs/heads/test_auto_gc >output 2>&1 &&
+	    grep "Auto packing the repository for optimum performance." output
+	) &&
+	test ! -e child/.git/objects/tmp_test_object
+'
+
 rewound_push_setup() {
 	rm -rf parent child &&
 	mkdir parent &&