Re: [PATCH 1/3] line-log: free diff queue when processing non-merge commits

> 
> On Mon, Nov 07 2022, SZEDER Gábor wrote:
> 
> > On Wed, Nov 02, 2022 at 08:20:21PM -0400, Taylor Blau wrote:
> >> > +void diff_free_queue(struct diff_queue_struct *q)
> >> > +{
> >> > +	for (int i = 0; i < q->nr; i++)
> >> > +		diff_free_filepair(q->queue[i]);
> >> > +	free(q->queue);
> >> > +}
> >> 
> >> Though I wonder, should diff_free_queue() be a noop when q is NULL? The
> >> caller in process_ranges_ordinary_commit() doesn't care, of course,
> >> since q is always non-NULL there.
> >> 
> >> But if we're making it part of the diff API, we should probably err on
> >> the side of flexibility.
> >
> > On one hand, strbuf_reset(), string_list_clear(), or strvec_clear()
> > would all segfault on a NULL strbuf, string_list, or strvec pointer.
> 
> But the reason we do that is because those APIs will always ensure that
> the struct is never in an inconsistent state, as opposed to the
> destructor you're adding here.

> I.e. if you were to work with the queue after this diff_free_queue()
> call in process_ranges_ordinary_commit() you'd segfault, not so with
> those other APIs.
> 
> > On the other hand, given the usage patterns of the diff API, and that
> > it mostly only works on the dreaded global 'diff_queued_diff'
> > instance, I don't think there is any flexibility to be gained with
> > this; indeed it is already more flexible than many diff API functions
> > as it works on the diff queue given as parameter instead of that
> > global instance.
> 
> I pointed how this could be nicer if you made it work like those other
> APIs in
> https://lore.kernel.org/git/221103.864jvg2yit.gmgdl@evledraar.gmail.com/;
> I.e. we could do away with DIFF_QUEUE_CLEAR() after calling this
> "free()".
> 
> But in lieu of such a larger change, just adding a call to
> "DIFF_QUEUE_CLEAR()" in this new free() function seems like it could
> make thing safer at very little cost.
> 
> We're also far from consistent about this, but I wish it worked like
> that and were called:
> 
> 	diff_queue_struct_{release,clear}()
> 
> I.e. the usual naming is:
> 
> 	<struct name>_{release,clear}()
> 
> In cases where we don't free() the pointer itself, but assume that we're
> working on a struct on the stack, whereas *_free() functions will free
> the malloc'd pointer itself, as well as anything it contains.
>