Re: [PATCH 2/2] peel_onion(): teach $foo^{object} peeler

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

While I was in the middle of suggesting documentation for this new
syntax, I discovered that you already added documentation to your repo
but didn't mention the new version on the mailing list (or maybe I
overlooked it).  It would be helpful if you would submit your own
changes to the mailing list to make it harder for the rest of us to
overlook them--and easier to look over them :-)

The documentation looks fine to me.

Off topic: Your patch reminds me of something else that surprised me:
there is no "$userstring^{tag}".  I suppose it would be a bit ambiguous,
given that tags can point at tags, and it would also be less useful than
the other suffixes.  But its absence irked the completionist in me :-)

Michael

On 04/01/2013 12:38 AM, Junio C Hamano wrote:
> A string that names an object can be suffixed with ^{type} peeler to
> say "I have this object name; peel it until you get this type. If
> you cannot do so, it is an error".  v1.8.2^{commit} asks for a commit
> that is pointed at an annotated tag v1.8.2; v1.8.2^{tree} unwraps it
> further to the top-level tree object.  A special suffix ^{} (i.e. no
> type specified) means "I do not care what it unwraps to; just peel
> annotated tag until you get something that is not a tag".
> 
> When you have a random user-supplied string, you can turn it to a
> bare 40-hex object name, and cause it to error out if such an object
> does not exist, with:
> 
> 	git rev-parse --verify "$userstring^{}"
> 
> for most objects, but this does not yield the tag object name when
> $userstring refers to an annotated tag.
> 
> Introduce a new suffix, ^{object}, that only makes sure the given
> name refers to an existing object.  Then
> 
> 	git rev-parse --verify "$userstring^{object}"
> 
> becomes a way to make sure $userstring refers to an existing object.
> 
> This is necessary because the plumbing "rev-parse --verify" is only
> about "make sure the argument is something we can feed to get_sha1()
> and turn it into a raw 20-byte object name SHA-1" and is not about
> "make sure that 20-byte object name SHA-1 refers to an object that
> exists in our object store".  When the given $userstring is already
> a 40-hex, by definition "rev-parse --verify $userstring" can turn it
> into a raw 20-byte object name.  With "$userstring^{object}", we can
> make sure that the 40-hex string names an object that exists in our
> object store before "--verify" kicks in.
> 
> Signed-off-by: Junio C Hamano <gitster@pobox.com>
> ---
>  sha1_name.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/sha1_name.c b/sha1_name.c
> index 45788df..85b6e75 100644
> --- a/sha1_name.c
> +++ b/sha1_name.c
> @@ -594,7 +594,7 @@ struct object *peel_to_type(const char *name, int namelen,
>  	while (1) {
>  		if (!o || (!o->parsed && !parse_object(o->sha1)))
>  			return NULL;
> -		if (o->type == expected_type)
> +		if (expected_type == OBJ_ANY || o->type == expected_type)
>  			return o;
>  		if (o->type == OBJ_TAG)
>  			o = ((struct tag*) o)->tagged;
> @@ -645,6 +645,8 @@ static int peel_onion(const char *name, int len, unsigned char *sha1)
>  		expected_type = OBJ_TREE;
>  	else if (!strncmp(blob_type, sp, 4) && sp[4] == '}')
>  		expected_type = OBJ_BLOB;
> +	else if (!prefixcmp(sp, "object}"))
> +		expected_type = OBJ_ANY;
>  	else if (sp[0] == '}')
>  		expected_type = OBJ_NONE;
>  	else if (sp[0] == '/')
> 


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