Subject: Re: [PATCH v2 04/11] reftable/stack: verify that `reftable_stack_add()` uses auto-compaction

From: Taylor Blau <[email-masked]>
Date: Fri, 8 Dec 2023 16:35:43 -0500

On Fri, Dec 08, 2023 at 03:53:10PM +0100, Patrick Steinhardt wrote:
> diff --git a/reftable/stack_test.c b/reftable/stack_test.c
> index 0644c8ad2e..c979d177c2 100644
> --- a/reftable/stack_test.c
> +++ b/reftable/stack_test.c
> @@ -850,6 +850,52 @@ static void test_reftable_stack_auto_compaction(void)
>  	clear_dir(dir);
>  }
>
> +static void test_reftable_stack_add_performs_auto_compaction(void)
> +{
> +	struct reftable_write_options cfg = { 0 };
> +	struct reftable_stack *st = NULL;
> +	char *dir = get_tmp_dir(__LINE__);
> +	int err, i, n = 20;
> +
> +	err = reftable_new_stack(&st, dir, cfg);
> +	EXPECT_ERR(err);
> +
> +	for (i = 0; i <= n; i++) {
> +		struct reftable_ref_record ref = {
> +			.update_index = reftable_stack_next_update_index(st),
> +			.value_type = REFTABLE_REF_SYMREF,
> +			.value.symref = "master",
> +		};
> +		char name[100];
> +
> +		/*
> +		 * Disable auto-compaction for all but the last runs. Like this
> +		 * we can ensure that we indeed honor this setting and have
> +		 * better control over when exactly auto compaction runs.
> +		 */
> +		st->disable_auto_compact = i != n;
> +
> +		snprintf(name, sizeof(name), "branch%04d", i);
> +		ref.refname = name;

Is there a reason that we have to use snprintf() here and not a strbuf?

I would have expected to see something like:

    struct strbuf buf = STRBUF_INIT;
    /* ... */
    strbuf_addf(&buf, "branch%04d", i);
    ref.refname = strbuf_detach(&buf, NULL);

I guess it doesn't matter too much, but I think if we can avoid using
snprintf(), it's worth doing. If we must use snprintf() here, we should
probably use Git's xsnprintf() instead.

> +		err = reftable_stack_add(st, &write_test_ref, &ref);
> +		EXPECT_ERR(err);
> +
> +		/*
> +		 * The stack length should grow continuously for all runs where
> +		 * auto compaction is disabled. When enabled, we should merge
> +		 * all tables in the stack.
> +		 */
> +		if (i != n)
> +			EXPECT(st->merged->stack_len == i + 1);
> +		else
> +			EXPECT(st->merged->stack_len == 1);

You could shorten this to

    EXPECT(st->merged->stack_len == (i == n ? 1 : i + 1);

But I like the version that you wrote here better, because it clearly
indicates when we should and should not perform compaction.

Thanks,
Taylor