Re: [PATCH v2] sequencer: fix edit handling for cherry-pick and revert messages

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi Elijah,

On Tue, 30 Mar 2021, Elijah Newren via GitGitGadget wrote:

> From: Elijah Newren <newren@gmail.com>
>
> save_opts() should save any non-default values.  It was intended to do
> this, but since most options in struct replay_opts default to 0, it only
> saved non-zero values.  Unfortunately, this does not always work for
> options.edit.  Roughly speaking, options.edit had a default value of 0
> for cherry-pick but a default value of 1 for revert.  Make save_opts()
> record a value whenever it differs from the default.
>
> options.edit was also overly simplistic; we had more than two cases.
> The behavior that previously existed was as follows:
>
>                        Non-conflict commits    Right after Conflict
>     revert             Edit iff isatty(0)      Edit (ignore isatty(0))
>     cherry-pick        No edit                 See above
>     Specify --edit     Edit (ignore isatty(0)) See above
>     Specify --no-edit  (*)                     See above
>
>     (*) Before stopping for conflicts, No edit is the behavior.  After
>         stopping for conflicts, the --no-edit flag is not saved so see
>         the first two rows.
>
> However, the expected behavior is:
>
>                        Non-conflict commits    Right after Conflict
>     revert             Edit iff isatty(0)      Edit iff isatty(0)
>     cherry-pick        No edit                 Edit iff isatty(0)
>     Specify --edit     Edit (ignore isatty(0)) Edit (ignore isatty(0))
>     Specify --no-edit  No edit                 No edit
>
> In order to get the expected behavior, we need to change options.edit
> to a tri-state: unspecified, false, or true.  When specified, we follow
> what it says.  When unspecified, we need to check whether the current
> commit being created is resolving a conflict as well as consulting
> options.action and isatty(0).  While at it, add a should_edit() utility
> function that compresses options.edit down to a boolean based on the
> additional information for the non-conflict case.
>
> continue_single_pick() is the function responsible for resuming after
> conflict cases, regardless of whether there is one commit being picked
> or many.  Make this function stop assuming edit behavior in all cases,
> so that it can correctly handle !isatty(0) and specific requests to not
> edit the commit message.

Nicely explained!

I'll allow myself one tangent: the subject of the sequencer's Unix shell
script heritage seems to come up with an increasing frequency, in
particular the awful "let's write out one file per setting" strategy.

I would _love_ for `save_opts()` to write a JSON instead (or an INI via
the `git_config_*()` family of functions, as is done already by the
cherry-pick/revert stuff), now that we no longer have any shell script
backend (apart from `--preserve-merges`, but that one is on its way out
anyway).

The one thing that concerns me with this idea is that I know for a fact
that some enterprisey users play games with those files inside
`<GIT_DIR>/rebase-merge` that should be considered internal implementation
details. Not sure how to deprecate that properly, I don't think we have a
sane way to detect whether users rely on these implementation details
other than breaking their expectations, which is not really a gentle way
to ask them to update their scripts.

> diff --git a/builtin/revert.c b/builtin/revert.c
> index 314a86c5621b..81441020231a 100644
> --- a/builtin/revert.c
> +++ b/builtin/revert.c
> @@ -182,7 +182,7 @@ static int run_sequencer(int argc, const char **argv, struct replay_opts *opts)
>  				"--signoff", opts->signoff,
>  				"--no-commit", opts->no_commit,
>  				"-x", opts->record_origin,
> -				"--edit", opts->edit,
> +				"--edit", opts->edit == 1,

Honestly, I'd prefer `> 0` here.

>  				NULL);
>
>  	if (cmd) {
> @@ -230,8 +230,6 @@ int cmd_revert(int argc, const char **argv, const char *prefix)
>  	struct replay_opts opts = REPLAY_OPTS_INIT;
>  	int res;
>
> -	if (isatty(0))
> -		opts.edit = 1;
>  	opts.action = REPLAY_REVERT;
>  	sequencer_init_config(&opts);
>  	res = run_sequencer(argc, argv, &opts);
> diff --git a/sequencer.c b/sequencer.c
> index 848204d3dc3f..d444c778a097 100644
> --- a/sequencer.c
> +++ b/sequencer.c
> @@ -1860,14 +1860,26 @@ static void record_in_rewritten(struct object_id *oid,
>  		flush_rewritten_pending();
>  }
>
> +static int should_edit(struct replay_opts *opts) {
> +	assert(opts->edit >= -1 && opts->edit <= 1);

Do we really want to introduce more of these useless `assert()`s? I know
that we stopped converting them to `BUG()`, but I really dislike
introducing new ones: they have very little effect, being no-ops by
default in most setups.

> +	if (opts->edit == -1)

Maybe `< 0`, as we do elsewhere for "not specified"?

> +		/*
> +		 * Note that we only handle the case of non-conflicted
> +		 * commits; continue_single_pick() handles the conflicted
> +		 * commits itself instead of calling this function.
> +		 */
> +		return (opts->action == REPLAY_REVERT && isatty(0)) ? 1 : 0;

Apart from the extra parentheses, that makes sense to me.

> +	return opts->edit;
> +}
> +
>  static int do_pick_commit(struct repository *r,
>  			  enum todo_command command,
>  			  struct commit *commit,
>  			  struct replay_opts *opts,
>  			  int final_fixup, int *check_todo)
>  {
> -	unsigned int flags = opts->edit ? EDIT_MSG : 0;
> -	const char *msg_file = opts->edit ? NULL : git_path_merge_msg(r);
> +	unsigned int flags = should_edit(opts) ? EDIT_MSG : 0;
> +	const char *msg_file = should_edit(opts) ? NULL : git_path_merge_msg(r);
>  	struct object_id head;
>  	struct commit *base, *next, *parent;
>  	const char *base_label, *next_label;
> @@ -3101,9 +3113,9 @@ static int save_opts(struct replay_opts *opts)
>  	if (opts->no_commit)
>  		res |= git_config_set_in_file_gently(opts_file,
>  					"options.no-commit", "true");
> -	if (opts->edit)
> -		res |= git_config_set_in_file_gently(opts_file,
> -					"options.edit", "true");
> +	if (opts->edit != -1)

s/!= -1/>= 0/

> +		res |= git_config_set_in_file_gently(opts_file, "options.edit",
> +						     opts->edit ? "true" : "false");
>  	if (opts->allow_empty)
>  		res |= git_config_set_in_file_gently(opts_file,
>  					"options.allow-empty", "true");
> @@ -4077,7 +4089,7 @@ static int pick_commits(struct repository *r,
>  	prev_reflog_action = xstrdup(getenv(GIT_REFLOG_ACTION));
>  	if (opts->allow_ff)
>  		assert(!(opts->signoff || opts->no_commit ||
> -			 opts->record_origin || opts->edit ||
> +			 opts->record_origin || should_edit(opts) ||
>  			 opts->committer_date_is_author_date ||
>  			 opts->ignore_date));
>  	if (read_and_refresh_cache(r, opts))
> @@ -4370,14 +4382,35 @@ static int pick_commits(struct repository *r,
>  	return sequencer_remove_state(opts);
>  }
>
> -static int continue_single_pick(struct repository *r)
> +static int continue_single_pick(struct repository *r, struct replay_opts *opts)
>  {
> -	const char *argv[] = { "commit", NULL };
> +	struct strvec argv = STRVEC_INIT;
> +	int want_edit;

Do we really want that extra `want_edit` variable? I think the code would
be easier to read without it, and still be obvious enough.

> +	int ret;
>
>  	if (!refs_ref_exists(get_main_ref_store(r), "CHERRY_PICK_HEAD") &&
>  	    !refs_ref_exists(get_main_ref_store(r), "REVERT_HEAD"))
>  		return error(_("no cherry-pick or revert in progress"));
> -	return run_command_v_opt(argv, RUN_GIT_CMD);
> +
> +	strvec_push(&argv, "commit");
> +
> +	/*
> +	 * continue_single_pick() handles the case of recovering from a
> +	 * conflict.  should_edit() doesn't handle that case; for a conflict,
> +	 * we want to edit if the user asked for it, or if they didn't specify
> +	 * and stdin is a tty.
> +	 */
> +	want_edit = (opts->edit == 1) || ((opts->edit == -1) && isatty(0));
> +	if (!want_edit)

Here is what I would prefer:

	if (!opts->edit || (opts->edit < 0 && !isatty(0)))

The rest looks good, and the comments are _really_ helpful.

And the remainder of the patch also looks good, so I will spare readers
time by not even quoting it.

Thank you!
Dscho