On 10/3/24 2:11 AM, Jeff King wrote:
On Wed, Oct 02, 2024 at 10:36:33PM -0400, Derrick Stolee wrote:
I do think this would have been a harder mistake to make if the callback
simply returned a "const char *" pointer. We'd lose the ability to show
prefixes with embedded NULs, but I'm not sure that's a big deal. It
would also help for line-log to use the existing helper rather than
inventing its own. So together on top something like this (which I'd
probably turn into two patches if this seems to others like it's
valuable and not just churn):
I do agree that changing the return type will make this easier to prevent
and the code should be easier to read as well.
Your diffed patch looks pretty good. I made an attempt at guessing where
you would have split them (first remove the duplicate method, then change
the method prototype and callers).
Yep, exactly. I actually ended up with a third patch which is a nearby
cleanup. I'll hold them back for now, though. Your patch is a regression
fix which we should prioritize (though it sounds like it is in 2.46, not
the upcoming 2.47?). I'll post my on top as a separate series.
I even took some time to attempt to remove the static strbuf from
diff_output_prefix_callback() in favor of using the 'data' member of the
diff_options struct, but it was not incredibly obvious how to communicate
ownership of the struct which would need to store both the graph struct
and the strbuf. Perhaps this would be good for #leftoverbits.
Yeah, I think probably "struct git_graph" would need to own the buffer,
initialize it in graph_init(), and then discard it in graph_clear().
But that gets weird because apparently you can set the callback without
a git_graph? Looks like that is triggered by "--line-prefix" without
"--graph". Yuck.
But in that case we are just showing the line_prefix string, so we could
return that directly. Something like the patch below.
The whole thing feels a bit over-engineered with the callback. The graph
code is the only one that needs anything beyond a static string. And the
way --line-prefix interacts with it is odd, since some callers override
the callback (e.g., "range-diff --line-prefix=foo" is accepted, but
doesn't do anything). I don't think there's a bug anybody cares about,
but, well...it's not how I would have written it. ;)
Thanks for exploring this with the diff you sent. It's subtle, but you
did a good job of recognizing that when the callback is used without
a 'graph' value, it returns opt->line_prefix.
+ if (!graph)
+ return opt->line_prefix;
I was wondering why there was no need to edit graph_setup_line_prefix()
in your diff, and this explains why. Your change is simple enough to
handle that change while being robust to a future assignment of the
callback data.
For what it's worth, I attempted creating a custom callback with a
BUG() statement in it and the only test failure was t4013-diff-various.sh.
That test is very non-standard, and it did not recognize the process
failure, only the output difference. #leftoverbits could make that test
fail on process failure.
Thanks,
-Stolee
