Subject: rebase: --fork-point regression fix

"git rebase --fork-point master" used to work OK, as it internally
called "git merge-base --fork-point" that knew how to handle short
refname and dwim it to the full refname before calling the
underlying get_fork_point() function.

This is no longer true after the command was rewritten in C, as its
internall call made directly to get_fork_point() does not dwim a
short ref.

Move the "dwim the refname argument to the full refname" logic that
is used in "git merge-base" to the underlying get_fork_point()
function, so that the other caller of the function in the
implementation of "git rebase" behaves the same way to fix this
regression.

---
 builtin/merge-base.c         | 12 +-----------
 commit.c                     | 15 +++++++++++++--
 t/t3431-rebase-fork-point.sh | 20 ++++++++++++++++++++
 3 files changed, 34 insertions(+), 13 deletions(-)

diff --git a/builtin/merge-base.c b/builtin/merge-base.c
index e3f8da13b6..6719ac198d 100644
--- a/builtin/merge-base.c
+++ b/builtin/merge-base.c

@@ -114,26 +114,16 @@ static int handle_is_ancestor(int argc, const char **argv)
 static int handle_fork_point(int argc, const char **argv)
 {
 	struct object_id oid;
-	char *refname;
 	struct commit *derived, *fork_point;
 	const char *commitname;
 
-	switch (dwim_ref(argv[0], strlen(argv[0]), &oid, &refname)) {
-	case 0:
-		die("No such ref: '%s'", argv[0]);
-	case 1:
-		break; /* good */
-	default:
-		die("Ambiguous refname: '%s'", argv[0]);
-	}
-

 	commitname = (argc == 2) ? argv[1] : "HEAD";
 	if (get_oid(commitname, &oid))
 		die("Not a valid object name: '%s'", commitname);
 
 	derived = lookup_commit_reference(the_repository, &oid);
 
-	fork_point = get_fork_point(refname, derived);
+	fork_point = get_fork_point(argv[0], derived);
 
 	if (!fork_point)
 		return 1;

diff --git a/commit.c b/commit.c
index 40890ae7ce..016f14fe95 100644
--- a/commit.c
+++ b/commit.c

@@ -903,12 +903,22 @@ struct commit *get_fork_point(const char *refname, struct commit *commit)
 	struct commit_list *bases;
 	int i;
 	struct commit *ret = NULL;
+	char *full_refname;
+
+	switch (dwim_ref(refname, strlen(refname), &oid, &full_refname)) {
+	case 0:
+		die("No such ref: '%s'", refname);
+	case 1:
+		break; /* good */
+	default:
+		die("Ambiguous refname: '%s'", refname);
+	}

 
 	memset(&revs, 0, sizeof(revs));
 	revs.initial = 1;
-	for_each_reflog_ent(refname, collect_one_reflog_ent, &revs);
+	for_each_reflog_ent(full_refname, collect_one_reflog_ent, &revs);
 
-	if (!revs.nr && !get_oid(refname, &oid))
+	if (!revs.nr)
 		add_one_commit(&oid, &revs);
 
 	for (i = 0; i < revs.nr; i++)

@@ -934,6 +944,7 @@ struct commit *get_fork_point(const char *refname, struct commit *commit)
 
 cleanup_return:
 	free_commit_list(bases);
+	free(full_refname);
 	return ret;
 }
 

diff --git a/t/t3431-rebase-fork-point.sh b/t/t3431-rebase-fork-point.sh
index 78851b9a2a..5b09aecd13 100755
--- a/t/t3431-rebase-fork-point.sh
+++ b/t/t3431-rebase-fork-point.sh

@@ -47,11 +47,31 @@ test_rebase 'G F B A' --keep-base
 test_rebase 'G F C E D B A' --no-fork-point
 test_rebase 'G F C D B A' --no-fork-point --onto D
 test_rebase 'G F C B A' --no-fork-point --keep-base
+
 test_rebase 'G F E D B A' --fork-point refs/heads/master
+test_rebase 'G F E D B A' --fork-point master
+
 test_rebase 'G F D B A' --fork-point --onto D refs/heads/master
+test_rebase 'G F D B A' --fork-point --onto D master
+
 test_rebase 'G F B A' --fork-point --keep-base refs/heads/master
+test_rebase 'G F B A' --fork-point --keep-base master
+
 test_rebase 'G F C E D B A' refs/heads/master
+test_rebase 'G F C E D B A' master
+
 test_rebase 'G F C D B A' --onto D refs/heads/master
+test_rebase 'G F C D B A' --onto D master
+
 test_rebase 'G F C B A' --keep-base refs/heads/master
+test_rebase 'G F C B A' --keep-base master
+
+test_expect_success "git rebase --fork-point with ambigous refname" "
+	git checkout master &&
+	git checkout -b one &&
+	git checkout side &&
+	git tag one &&
+	test_must_fail git rebase --fork-point --onto D one
+"