Re: [GSoC][PATCH v4 2/3] rebase -i: rewrite checkout_onto() in C
From: Junio C Hamano <hidden>
Date: 2018-06-26 17:35:08
Alban Gruin [off-list ref] writes:
This rewrites checkout_onto() from shell to C. The new version is called detach_onto(), given its role.
The name, given its role, may be good, but is the implementtaion robust enough to fulfill the promise its name gives?
quoted hunk
git rebase--helper --check-todo-list || { ret=$? - checkout_onto + git rebase--helper --detach-onto "$onto_name" "$onto" \ + "$orig_head" ${verbose:+--verbose}
Here, $onto_name is what the end-user gave us (e.g. it is "master..." in "git rebase --onto=master... base"), while $onto is a 40-hex object name of the commit. $orig_head is also a 40-hex object name. And this call shows how the above shell scriptlet calls into the detach_onto() thing ...
+ if (command == DETACH_ONTO && argc == 4) + return !!detach_onto(&opts, argv[1], argv[2], argv[3], verbose);
... which is defined like so:
quoted hunk
+int detach_onto(struct replay_opts *opts, + const char *onto_name, const char *onto, + const char *orig_head, unsigned verbose) +{ + struct object_id oid; + const char *action = reflog_message(opts, "start", "checkout %s", onto_name); + + if (get_oid(orig_head, &oid)) + return error(_("%s: not a valid OID"), orig_head);
Which means that this can be more strict to use get_oid_hex() to catch possible mistakes in the caller.
+ if (run_git_checkout(opts, onto, verbose, action)) {And this could be a bit problematic, as we can see below how the "checkout" thing does not guarantee "detaching" at all ...
quoted hunk
+ apply_autostash(opts); + sequencer_remove_state(opts); + return error(_("could not detach HEAD")); + } + + return update_ref(NULL, "ORIG_HEAD", &oid, NULL, 0, UPDATE_REFS_MSG_ON_ERR); +} +
... which can be seen here ...
quoted hunk
+static int run_git_checkout(struct replay_opts *opts, const char *commit, + int verbose, const char *action) +{ + struct child_process cmd = CHILD_PROCESS_INIT; + + cmd.git_cmd = 1; + + argv_array_push(&cmd.args, "checkout"); + argv_array_push(&cmd.args, commit); + argv_array_pushf(&cmd.env_array, GIT_REFLOG_ACTION "=%s", action); + + if (verbose) + return run_command(&cmd); + else + return run_command_silent_on_success(&cmd); +}
This drives the external command "git checkout" with _any_ string
the caller passes in "commit". If the variable happens to have
'master', for example, it would be "git checkout master" and if you
have a branch with that name, it will not detach but check out the
branch to build on it. It is a caller's responsibility to give a
suitable "commit" if it wants to use this helper to detach.
So perhaps the caller of this function in detach_onto() should pass
"%s^0" or even do something like
struct object_id onto_oid;
char onto_hex[GIT_MAX_HEXSZ + 1];
if (get_oid(onto, &onto_oid) || oid_to_hex_r(onto_hex, &onto_oid))
return error(...);
if (run_git_checkout(opts, onto_hex, verbose, action)) {
...
to ensure that it keeps the promise its name gives.
I can hear "Oh, but it is a bug in the caller to give anything that
won't result in detaching in 'onto'" but that is not a valid excuse,
given that this _public_ function is called "detach_onto". Making
sure detachment happens is its responsibility, not its callers'.
Or we could do a cop-out alternative of commenting the function in *.h
file to say "onto must be given as 40-hex", with a code to make sure
the caller really gave us a 40-hex and not a branch name. That is a
less ideal but probably acceptable alternative.
quoted hunk
static const char rescheduled_advice[] = N_("Could not execute the todo command\n" "\n"diff --git a/sequencer.h b/sequencer.h index 35730b13e..9f0ac5e75 100644 --- a/sequencer.h +++ b/sequencer.h@@ -100,6 +100,10 @@ int update_head_with_reflog(const struct commit *old_head, void commit_post_rewrite(const struct commit *current_head, const struct object_id *new_head); +int detach_onto(struct replay_opts *opts, + const char *onto_name, const char *onto, + const char *orig_head, unsigned verbose); + #define SUMMARY_INITIAL_COMMIT (1 << 0) #define SUMMARY_SHOW_AUTHOR_DATE (1 << 1) void print_commit_summary(const char *prefix, const struct object_id *oid,