Re: [PATCH 1/2] pack-refs: write peeled entry for non-tags

[Michael Haggerty <mhagger@alum.mit.edu>]

Looks good aside from a couple of minor points mentioned below.

On 03/16/2013 10:01 AM, Jeff King wrote:
> When we pack an annotated tag ref, we write not only the
> sha1 of the tag object along with the ref, but also the sha1
> obtained by peeling the tag. This lets readers of the
> pack-refs file know the peeled value without having to
> actually load the object, speeding up upload-pack's ref
> advertisement.
> 
> The writer marks a packed-refs file with peeled refs using
> the "peeled" trait at the top of the file. When the reader
> sees this trait, it knows that each ref is either followed
> by its peeled value, or it is not an annotated tag.
> 
> However, there is a mismatch between the assumptions of the
> reader and writer. The writer will only peel refs under
> refs/tags, but the reader does not know this; it will assume
> a ref without a peeled value must not be a tag object. Thus
> an annotated tag object placed outside of the refs/tags
> hierarchy will not have its peeled value printed by
> upload-pack.
> 
> The simplest way to fix this is to start writing peel values
> for all refs. This matches what the reader expects for both
> new and old versions of git.
> 
> Signed-off-by: Jeff King <peff@peff.net>

I like your explanation of the problem.

> ---
>  pack-refs.c         | 16 ++++++++--------
>  t/t3211-peel-ref.sh | 42 ++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 50 insertions(+), 8 deletions(-)
>  create mode 100755 t/t3211-peel-ref.sh
> 
> diff --git a/pack-refs.c b/pack-refs.c
> index f09a054..10832d7 100644
> --- a/pack-refs.c
> +++ b/pack-refs.c
> @@ -27,6 +27,7 @@ static int handle_one_ref(const char *path, const unsigned char *sha1,
>  			  int flags, void *cb_data)
>  {
>  	struct pack_refs_cb_data *cb = cb_data;
> +	struct object *o;
>  	int is_tag_ref;
>  
>  	/* Do not pack the symbolic refs */
> @@ -39,14 +40,13 @@ static int handle_one_ref(const char *path, const unsigned char *sha1,
>  		return 0;
>  
>  	fprintf(cb->refs_file, "%s %s\n", sha1_to_hex(sha1), path);
> -	if (is_tag_ref) {
> -		struct object *o = parse_object(sha1);
> -		if (o->type == OBJ_TAG) {
> -			o = deref_tag(o, path, 0);
> -			if (o)
> -				fprintf(cb->refs_file, "^%s\n",
> -					sha1_to_hex(o->sha1));
> -		}
> +
> +	o = parse_object(sha1);
> +	if (o->type == OBJ_TAG) {

You suggested that I add a test (o != NULL) at the equivalent place in
my code (which was derived from this code).  Granted, my code was
explicitly intending to pass invalid SHA1 values to parse_object().  But
wouldn't it be a good defensive step to add the same check here?

> +		o = deref_tag(o, path, 0);
> +		if (o)
> +			fprintf(cb->refs_file, "^%s\n",
> +				sha1_to_hex(o->sha1));
>  	}
>  
>  	if ((cb->flags & PACK_REFS_PRUNE) && !do_not_prune(flags)) {
> diff --git a/t/t3211-peel-ref.sh b/t/t3211-peel-ref.sh
> new file mode 100755
> index 0000000..dd5b48b
> --- /dev/null
> +++ b/t/t3211-peel-ref.sh
> @@ -0,0 +1,42 @@
> +#!/bin/sh
> +
> +test_description='tests for the peel_ref optimization of packed-refs'
> +. ./test-lib.sh
> +
> +test_expect_success 'create annotated tag in refs/tags' '
> +	test_commit base &&
> +	git tag -m annotated foo
> +'
> +
> +test_expect_success 'create annotated tag outside of refs/tags' '
> +	git update-ref refs/outside/foo refs/tags/foo
> +'
> +
> +# This matches show-ref's output
> +print_ref() {
> +	echo "`git rev-parse "$1"` $1"
> +}
> +

CodingGuidelines prefers $() over ``.

> +test_expect_success 'set up expected show-ref output' '
> +	{
> +		print_ref "refs/heads/master" &&
> +		print_ref "refs/outside/foo" &&
> +		print_ref "refs/outside/foo^{}" &&
> +		print_ref "refs/tags/base" &&
> +		print_ref "refs/tags/foo" &&
> +		print_ref "refs/tags/foo^{}"
> +	} >expect
> +'
> +
> +test_expect_success 'refs are peeled outside of refs/tags (loose)' '
> +	git show-ref -d >actual &&
> +	test_cmp expect actual
> +'
> +
> +test_expect_success 'refs are peeled outside of refs/tags (packed)' '
> +	git pack-refs --all &&
> +	git show-ref -d >actual &&
> +	test_cmp expect actual
> +'
> +
> +test_done
> 


-- 
Michael Haggerty
mhagger@alum.mit.edu
http://softwareswirl.blogspot.com/