Junio C Hamano <gitster@xxxxxxxxx> writes:
> "Avery Pennarun" <apenwarr@xxxxxxxxx> writes:
> ...
>> 1) Checking out a remote branch "git checkout origin/master" detaches
>> my HEAD, which is kind of bad, since it's such a common thing to want
>> to do.
>
> I do not think it is bad at all. The feature to detach HEAD was designed
> for that kind of usage. Start sightseeing, possibly futz with the code,
> and even create some snapshot commits, and then:
>
> * if it starts to take a usable shape, say "git checkout -b my-topic",
> from there, to give your exploration a lasting home; or
>
> * if it doesn't pan out, just discard it with "git checkout -f master"
> (or whatever you wanted to switch back to).
>
> One thing that might help for downstream people would be to be able to say
> "I am making 'my-topic' branch out of a detached HEAD, but it really is
> meant to be a fork of origin/master that I detached my HEAD from, so
> please set up tracking for that one".
>
> You could force people to say "git checkout -b my-topic origin/master"
> from the beginning, but that is very unreasonable and unworkable. When
> you are exploring, you more often than not do not know where your quest
> would lead to until spending some time. It is quite important to be able
> to delay the decision to create a local branch to keep what you did, and
> (more importantly) to be able to delay deciding what to name that topic.
>
> Perhaps "git checkout -b my-topic" from a detached HEAD should inspect the
> HEAD reflog to see which remote (or local) branch you came from, and give
> that to the --track logic.
So here is a patch for discussion, not heavily tested, but:
$ git checkout origin/master
$ git commit; hack hack hack ...
$ git checkout --track -b mybranch
sequence should result in mybranch tracking the 'master' branch from the
'origin'.
The patch is just a proof of concept; doing this for HEAD reflog that is
several megabytes long might take nontrivial amount of time (at least from
performance standard of git); if we wanted to go this route, we should add
an API to read the reflog entries from more recent to older.
branch.c | 59 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 59 insertions(+), 0 deletions(-)
diff --git c/branch.c w/branch.c
index b1e59f2..2ec6418 100644
--- c/branch.c
+++ w/branch.c
@@ -48,6 +48,62 @@ static int should_setup_rebase(const struct tracking *tracking)
}
/*
+ * A branch is created out of "HEAD" and we would want tracking;
+ * go back the reflog to figure out where we really came from.
+ */
+static int refine_head_one(const char *name, size_t namelen,
+ struct strbuf *found_ref)
+{
+ char *real_ref;
+ unsigned char sha1[20];
+ if (dwim_ref(name, namelen, sha1, &real_ref) != 1)
+ return 0;
+ strbuf_reset(found_ref);
+ strbuf_addstr(found_ref, real_ref);
+ return 0;
+}
+
+static int one_head_ent(unsigned char *osha1, unsigned char *nsha1,
+ const char *ident, unsigned long timestamp, int zone,
+ const char *message, void *cbdata)
+{
+ /*
+ * Look for signs of HEAD coming from elsewhere.
+ *
+ * "checkout: moving from %*s to %s" done by "git checkout"
+ * "%s: updating HEAD" done by "git reset"
+ */
+ struct strbuf *found_ref = cbdata;
+ char *cp;
+ size_t len;
+
+ if (!prefixcmp(message, "checkout: moving from ")) {
+ cp = strstr(message, " to ");
+ if (!cp)
+ return 0;
+ cp += 4;
+ len = strlen(cp);
+ if (cp[len-1] == '\n')
+ len--;
+ return refine_head_one(cp, len, found_ref);
+ }
+
+ cp = strstr(message, ": updating HEAD");
+ if (cp && !cp[15])
+ return refine_head_one(message, cp - message, found_ref);
+ return 0;
+}
+
+static const char *refine_head_ref(void)
+{
+ struct strbuf found = STRBUF_INIT;
+
+ strbuf_addstr(&found, "HEAD");
+ for_each_reflog_ent("HEAD", one_head_ent, &found);
+ return strbuf_detach(&found, NULL);
+}
+
+/*
* This is called when new_ref is branched off of orig_ref, and tries
* to infer the settings for branch.<new_ref>.{remote,merge} from the
* config.
@@ -58,6 +114,9 @@ static int setup_tracking(const char *new_ref, const char *orig_ref,
char key[1024];
struct tracking tracking;
+ if (!strcmp(orig_ref, "HEAD"))
+ orig_ref = refine_head_ref();
+
if (strlen(new_ref) > 1024 - 7 - 7 - 1)
return error("Tracking not set up: name too long: %s",
new_ref);
--
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