bisect: fix handling of `help` and invalid subcommands

As documented in git-bisect(1), `git bisect help` should display usage
information. However, since the migration of `git bisect` to a full
builtin command in 73fce29427 (Turn `git bisect` into a full built-in,
2022-11-10), this behavior was broken. Running `git bisect help` would,
instead of showing usage, either fail silently if already in a bisect
session, or otherwise trigger an interactive autostart prompt asking "Do
you want me to do it for you [Y/n]?".

Similarly, since df63421be9 (bisect--helper: handle states directly,
2022-11-10), running invalid subcommands like `git bisect foobar` also
led to the same behavior.

This occurred because `help` and other unrecognized subcommands were
being unconditionally passed to `bisect_state`, which then called
`bisect_autostart`, triggering the interactive prompt.

Fix this by:
1. Adding explicit handling for the `help` subcommand to show usage;
2. Validating that unrecognized commands are actually valid state
   commands before calling `bisect_state`;
3. Showing an error with usage for truly invalid commands.

This ensures that `git bisect help` displays the usage as documented,
and invalid commands fail cleanly without entering interactive mode.
Alternate terms are still handled correctly through
`check_and_set_terms`.

Signed-off-by: Ruoyu Zhong <zhongruoyu@outlook.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin/bisect.c b/builtin/bisect.c
index 8b8d870cd1ef0845ae28aa9295a1d6c4db81d984..993caf545dbd2c3c84a869e3b63e89c28af40c28 100644 (file)
--- a/builtin/bisect.c
+++ b/builtin/bisect.c
@@ -1453,9 +1453,13 @@ int cmd_bisect(int argc,
                if (!argc)
                        usage_msg_opt(_("need a command"), git_bisect_usage, options);
 
+               if (!strcmp(argv[0], "help"))
+                       usage_with_options(git_bisect_usage, options);
+
                set_terms(&terms, "bad", "good");
                get_terms(&terms);
-               if (check_and_set_terms(&terms, argv[0]))
+               if (check_and_set_terms(&terms, argv[0]) ||
+                   !one_of(argv[0], terms.term_good, terms.term_bad, NULL))
                        usage_msg_optf(_("unknown command: '%s'"), git_bisect_usage,
                                       options, argv[0]);
                res = bisect_state(&terms, argc, argv);