Re: [PATCH 1/2] sha1_name.c: signal if @{-N} was a true branch nameor a detached head
On Thu, May 09, 2013 at 10:08:24AM -0700, Junio C Hamano wrote:
Jeff King p...@peff.net writes:
Since the point of marking the detached HEAD is to turn off things like
@{-1}@{u}, we would want to be generous and err on the side of
assuming it is a branch if it _might_ be one.
I am not sure X and Y mesh well in your Since X, we would want Y.
It seems to argue for erring on the side of detached HEAD to me.
Thinking on it more, I don't see that one is actually better than the
other. If you claim a detached HEAD when there isn't one, the user says
stupid git, that was a branch, and you should tell me its upstream.
But if you claim an undetached HEAD when there isn't one, asking for the
upstream provides wildly inaccurate results (e.g., git checkout
@{-1}@{u} taking you somewhere unexpected).
Checking the from name $HEX against old_sha1 is a local and cheap
measure I added there for the first level of disambiguation. If
they do not match, we _know_ we didn't come back from a detached
HEAD state.
In order to err on the favor branch when it could have been one,
you could additionally look for the reflog .git/logs/refs/heads/$HEX
when the from name $HEX matches old_sha1 (which is likely to be
detached, but it is possible that we were on the $HEX branch when
its tip was at $HEX) and making sure the tip of that $HEX branch
once used to be at $HEX at the time recorded for @{-N} in the HEAD
reflog in question.
I was thinking in terms of @{-1}@{u}, so that you could say well, do we
have upstream config for such a branch currently?. Because even though
we are digging into history (and it _may_ have been a branch at the
time, but isn't now), if we are ultimately going to ask about the
upstream config (as it is _now_, not when the entry was made), then it
does not matter if the branch was detached or not: we are still going to
return failure either way.
But there are _other_ uses for @{-1}, and I am probably being too
focused on this one use-case.
So given all of the above, I think I am fine with the direction of the
series.
-Peff
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Re: [PATCH 1/2] sha1_name.c: signal if @{-N} was a true branch nameor a detached head
On Wed, May 08, 2013 at 02:12:29PM -0700, Junio C Hamano wrote:
The original API read checkout: moving from (.*) to ... from the
reflog of the HEAD, and returned the substring between from and
to, but there was no way, if the substring was a 40-hex string, to
tell if we were on a detached HEAD at that commit object, or on a
branch whose name happened to be the 40-hex string.
At this point, we cannot afford to change the format recorded in the
reflog, so introduce a heuristics to see if the 40-hex matches the
object name of the commit we are switching out of. This will
unfortunately mishandle this case:
HEX=$(git rev-parse master)
git checkout -b $HEX master
git checkout master
I do not think I've ever seen a 40-hex branch name in practice, but I
would think a branch named after the commit tip would be a reasonably
common reason to have one, and would trigger this case.
Since the point of marking the detached HEAD is to turn off things like
@{-1}@{u}, we would want to be generous and err on the side of
assuming it is a branch if it _might_ be one. IOW, shouldn't we treat
the above sequence as a branch, and therefore mishandle:
git checkout $HEX^0 master
git checkout master
by erroneously assuming that we moved to the branch $HEX?
-Peff
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Re: [PATCH 1/2] sha1_name.c: signal if @{-N} was a true branch nameor a detached head
Jeff King p...@peff.net writes:
Since the point of marking the detached HEAD is to turn off things like
@{-1}@{u}, we would want to be generous and err on the side of
assuming it is a branch if it _might_ be one.
I am not sure X and Y mesh well in your Since X, we would want Y.
It seems to argue for erring on the side of detached HEAD to me.
Checking the from name $HEX against old_sha1 is a local and cheap
measure I added there for the first level of disambiguation. If
they do not match, we _know_ we didn't come back from a detached
HEAD state.
In order to err on the favor branch when it could have been one,
you could additionally look for the reflog .git/logs/refs/heads/$HEX
when the from name $HEX matches old_sha1 (which is likely to be
detached, but it is possible that we were on the $HEX branch when
its tip was at $HEX) and making sure the tip of that $HEX branch
once used to be at $HEX at the time recorded for @{-N} in the HEAD
reflog in question.
That is far more expensive, though; I doubt it is worth doing.
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Re: [PATCH 1/2] sha1_name.c: signal if @{-N} was a true branch nameor a detached head
On Wed, May 8, 2013 at 5:12 PM, Junio C Hamano gits...@pobox.com wrote:
sha1_name.c: signal if @{-N} was a true branch nameor a detached head
s/nameor/name or/
The original API read checkout: moving from (.*) to ... from the
reflog of the HEAD, and returned the substring between from and
to, but there was no way, if the substring was a 40-hex string, to
tell if we were on a detached HEAD at that commit object, or on a
branch whose name happened to be the 40-hex string.
At this point, we cannot afford to change the format recorded in the
reflog, so introduce a heuristics to see if the 40-hex matches the
object name of the commit we are switching out of. This will
unfortunately mishandle this case:
HEX=$(git rev-parse master)
git checkout -b $HEX master
git checkout master
where we were indeed on a non-detached $HEX branch (i.e. HEAD was
pointing at refs/heads/$HEX, not storing $HEX), of course, but
otherwise should be fairly reliable.
Signed-off-by: Junio C Hamano gits...@pobox.com
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[PATCH 1/2] sha1_name.c: signal if @{-N} was a true branch nameor a detached head
The original API read checkout: moving from (.*) to ... from the
reflog of the HEAD, and returned the substring between from and
to, but there was no way, if the substring was a 40-hex string, to
tell if we were on a detached HEAD at that commit object, or on a
branch whose name happened to be the 40-hex string.
At this point, we cannot afford to change the format recorded in the
reflog, so introduce a heuristics to see if the 40-hex matches the
object name of the commit we are switching out of. This will
unfortunately mishandle this case:
HEX=$(git rev-parse master)
git checkout -b $HEX master
git checkout master
where we were indeed on a non-detached $HEX branch (i.e. HEAD was
pointing at refs/heads/$HEX, not storing $HEX), of course, but
otherwise should be fairly reliable.
Signed-off-by: Junio C Hamano gits...@pobox.com
---
* This is a preparatory step for the beginning of a much larger
series. Peff is Cc'ed because one of the most tricky issue
involves what d46a8301930a (fix parsing of @{-1}@{u} combination,
2010-01-28) did.
sha1_name.c | 16 ++--
1 file changed, 14 insertions(+), 2 deletions(-)
diff --git a/sha1_name.c b/sha1_name.c
index 3820f28..1473bb6 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -862,6 +862,7 @@ static int get_sha1_oneline(const char *prefix, unsigned
char *sha1,
struct grab_nth_branch_switch_cbdata {
int remaining;
struct strbuf buf;
+ int detached;
};
static int grab_nth_branch_switch(unsigned char *osha1, unsigned char *nsha1,
@@ -880,9 +881,14 @@ static int grab_nth_branch_switch(unsigned char *osha1,
unsigned char *nsha1,
if (!match || !target)
return 0;
if (--(cb-remaining) == 0) {
+ unsigned char sha1[20];
+
len = target - match;
strbuf_reset(cb-buf);
strbuf_add(cb-buf, match, len);
+ cb-detached = (len == 40
+ !get_sha1_hex(match, sha1)
+ !hashcmp(osha1, sha1));
return 1; /* we are done */
}
return 0;
@@ -891,8 +897,12 @@ static int grab_nth_branch_switch(unsigned char *osha1,
unsigned char *nsha1,
/*
* Parse @{-N} syntax, return the number of characters parsed
* if successful; otherwise signal an error with negative value.
+ * The string in buf.buf is either a branch name (needs to be
+ * prefixed with refs/heads/ if the caller wants to make it
+ * a fully spelled refname) or 40-hex object name of the detached
+ * HEAD, and *detached is set to true for the latter.
*/
-static int interpret_nth_prior_checkout(const char *name, struct strbuf *buf)
+static int interpret_nth_prior_checkout(const char *name, struct strbuf *buf,
int *detached)
{
long nth;
int retval;
@@ -917,6 +927,8 @@ static int interpret_nth_prior_checkout(const char *name,
struct strbuf *buf)
if (0 for_each_reflog_ent_reverse(HEAD, grab_nth_branch_switch,
cb)) {
strbuf_reset(buf);
strbuf_add(buf, cb.buf.buf, cb.buf.len);
+ if (detached)
+ *detached = cb.detached;
retval = brace - name + 1;
}
@@ -992,7 +1004,7 @@ int interpret_branch_name(const char *name, struct strbuf
*buf)
char *cp;
struct branch *upstream;
int namelen = strlen(name);
- int len = interpret_nth_prior_checkout(name, buf);
+ int len = interpret_nth_prior_checkout(name, buf, NULL);
int tmp_len;
if (!len)
--
1.8.3-rc1-182-gc61d106
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