Merge branch 'bc/receive-pack-stdout-protection'

When "git push" triggered the automatic gc on the receiving end, a
message from "git prune" that said it was removing cruft leaked to
the standard output, breaking the communication protocol.

* bc/receive-pack-stdout-protection:
  receive-pack: do not leak output from auto-gc to standard output
  t/t5400: demonstrate breakage caused by informational message from prune

builtin/receive-pack.c

@@ -977,7 +977,8 @@ int cmd_receive_pack(int argc, const char **argv, const char *prefix)
 			const char *argv_gc_auto[] = {
 				"gc", "--auto", "--quiet", NULL,
 			};
-			run_command_v_opt(argv_gc_auto, RUN_GIT_CMD);
+			int opt = RUN_GIT_CMD | RUN_COMMAND_STDOUT_TO_STDERR;
+			run_command_v_opt(argv_gc_auto, opt);
 		}
 		if (auto_update_server_info)
 			update_server_info(0);

t/t5400-send-pack.sh

@@ -145,6 +145,41 @@ test_expect_success 'push --all excludes remote-tracking hierarchy' '
 	)
 '
 
+test_expect_success '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 &&