Subject: Re: [PATCH 2/2] config: let feature.experimental imply gc.cruftPacks=true

From: Junio C Hamano <[email-masked]>
Date: Wed, 03 Aug 2022 15:05:47 -0700

Emily Shaffer <[email-masked]> writes:

> +* `gc.cruftPacks=true` reduces disk space used by unreachable objects during
> +garbage collection.

OK.

> diff --git a/builtin/gc.c b/builtin/gc.c
> index eeff2b760e..919cc508c5 100644
> --- a/builtin/gc.c
> +++ b/builtin/gc.c
> @@ -136,6 +136,7 @@ static int gc_config_is_timestamp_never(const char *var)
>  static void gc_config(void)
>  {
>  	const char *value;
> +	int experimental = 0;
>  
>  	if (!git_config_get_value("gc.packrefs", &value)) {
>  		if (value && !strcmp(value, "notbare"))
> @@ -148,6 +149,11 @@ static void gc_config(void)
>  	    gc_config_is_timestamp_never("gc.reflogexpireunreachable"))
>  		prune_reflogs = 0;
>  
> +	/* feature.experimental implies gc.cruftPacks=true */
> +	git_config_get_bool("feature.experimental", &experimental);
> +	if (experimental)
> +		cruft_packs = 1;
> +

I suspect the whole thing can just be:

	git_config_get_bool("feature.experimental", &cruft_packs);

If there is no feature.experimental configuration, the call returns
non-zero (we do not check, though) without touching &cruft_packs, if
there is feature.experimental configuration, the call returns zero
(we do not check, though) and cruft_packs is set to either true
(when experimental) or false (otherwise).

And this whole thing happens before we inspect what the more
specific configuration gc.cruftPacks says, so...

> diff --git a/t/t6500-gc.sh b/t/t6500-gc.sh
> index e4c2c3583d..4ab6750111 100755
> --- a/t/t6500-gc.sh
> +++ b/t/t6500-gc.sh
> @@ -238,6 +238,41 @@ test_expect_success 'gc.cruftPacks=true generates a cruft pack' '
>  	)
>  '
>  
> +test_expect_success 'feature.experimental=true generates a cruft pack' '
> +	git init crufts &&
> +	test_when_finished "rm -fr crufts" &&
> +	(
> +		cd crufts &&
> +		test_commit base &&
> +
> +		test_commit --no-tag foo &&
> +		test_commit --no-tag bar &&
> +		git reset HEAD^^ &&
> +
> +		git -c feature.experimental=true gc &&
> +
> +		cruft=$(basename $(ls .git/objects/pack/pack-*.mtimes) .mtimes) &&
> +		test_path_is_file .git/objects/pack/$cruft.pack
> +	)
> +'
> +
> +test_expect_success 'feature.experimental=false allows explicit cruft packs' '
> +	git init crufts &&
> +	test_when_finished "rm -fr crufts" &&
> +	(
> +		cd crufts &&
> +		test_commit base &&
> +
> +		test_commit --no-tag foo &&
> +		test_commit --no-tag bar &&
> +		git reset HEAD^^ &&
> +
> +		git -c gc.cruftPacks=true -c feature.experimental=false gc &&

OK.  

What is not tested is setting feature.experimental explicitly to
false without touching gc.cruftPacks does not use the cruft pack.