[PATCH] sha1_name: accept output of git-describe

[PATCH] sha1_name: accept output of git-describe

[Johannes Schindelin]

Now, 'git log $(git describe)' does the same as 'git log'.

NOTE: it might be possible that the unique abbreviation generated by
git-describe is no longer unique at a later stage. Evidently, in this
case the sha1 resolution fails.

Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
---
 sha1_name.c |   12 ++++++++++++
 1 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/sha1_name.c b/sha1_name.c
index b497528..c1f6cca 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -159,6 +159,18 @@ static int get_short_sha1(const char *na
 
 	if (len < MINIMUM_ABBREV)
 		return -1;
+
+	/* check for output of git-describe */
+	if (len > MINIMUM_ABBREV + 2) {
+		int i;
+		for (i = len - MINIMUM_ABBREV - 2; i > 0 && name[i] != '-'; i--)
+			; /* do nothing */
+		if (i > 0 && name[i + 1] == 'g') {
+			name += i + 2;
+			len -= i + 2;
+		}
+	}
+
 	hashclr(res);
 	memset(canonical, 'x', 40);
 	for (i = 0; i < len ;i++) {
-- 
1.4.2.1.ga0df5-dirty

Re: [PATCH] sha1_name: accept output of git-describe

[Junio C Hamano]

Johannes Schindelin <Johannes.Schindelin@gmx.de> writes:

> Now, 'git log $(git describe)' does the same as 'git log'.
>
> NOTE: it might be possible that the unique abbreviation generated by
> git-describe is no longer unique at a later stage. Evidently, in this
> case the sha1 resolution fails.
>
> Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
> ---
>  sha1_name.c |   12 ++++++++++++
>  1 files changed, 12 insertions(+), 0 deletions(-)
>
> diff --git a/sha1_name.c b/sha1_name.c
> index b497528..c1f6cca 100644
> --- a/sha1_name.c
> +++ b/sha1_name.c
> @@ -159,6 +159,18 @@ static int get_short_sha1(const char *na
>  
>  	if (len < MINIMUM_ABBREV)
>  		return -1;
> +
> +	/* check for output of git-describe */
> +	if (len > MINIMUM_ABBREV + 2) {
> +		int i;
> +		for (i = len - MINIMUM_ABBREV - 2; i > 0 && name[i] != '-'; i--)
> +			; /* do nothing */
> +		if (i > 0 && name[i + 1] == 'g') {
> +			name += i + 2;
> +			len -= i + 2;
> +		}
> +	}
> +

Shouldn't you also verify the leading ref (most likely a tag)
exists (and optionally check that it precedes the commit you
decoded into, but that is probably more expensive than it's
worth)?

Re: [PATCH] sha1_name: accept output of git-describe

[Johannes Schindelin]

Hi,

On Wed, 20 Sep 2006, Junio C Hamano wrote:

> Shouldn't you also verify the leading ref (most likely a tag)
> exists (and optionally check that it precedes the commit you
> decoded into, but that is probably more expensive than it's
> worth)?

I debated this with myself. But there is the cost, and more importantly 
the possibility that your victim^H^H^H^H^H^Hother side does not have the 
tag at all (for whatever reasons).

Ciao,
Dscho

Re: [PATCH] sha1_name: accept output of git-describe

[Shawn Pearce]

Junio C Hamano <junkio@cox.net> wrote:
> Johannes Schindelin <Johannes.Schindelin@gmx.de> writes:
> 
> > Now, 'git log $(git describe)' does the same as 'git log'.
> >
> > NOTE: it might be possible that the unique abbreviation generated by
> > git-describe is no longer unique at a later stage. Evidently, in this
> > case the sha1 resolution fails.
[snip]
> Shouldn't you also verify the leading ref (most likely a tag)
> exists (and optionally check that it precedes the commit you
> decoded into, but that is probably more expensive than it's
> worth)?

I thought the same thing when I first posted that it was probably
an easy change to this code (and then didn't do it myself) and
again when I read Johannes' implementation.  Both times I agreed
with you Junio that it was probably too expensive and not worth
doing.

Most of the time we assume not only that the SHA1 itself is unique
but also that it some hex character prefix is unique (such as 6 or
8 digits).  One might be able to argue that if we have duplicate
commits (when abbreviated) that you might be able to break the tie by
looking at the tag but even then you may not always be able to do so.

So no, probably not worth it...

-- 
Shawn.