checkout -b <name>: correctly detect existing branch

When create a new branch, we fed "refs/heads/<proposed name>" as a string
to get_sha1() and expected it to fail when a branch already exists.

The right way to check if a ref exists is to check with resolve_ref().

A naïve solution that might appear attractive but does not work is to
forbid slashes in get_describe_name() but that will not work. A describe
name is is in the form of "ANYTHING-g<short sha1>", and that ANYTHING part
comes from a original tag name used in the repository the user ran the
describe command. A sick user could have a confusing hierarchical tag
whose name is "refs/heads/foobar" (stored as refs/tags/refs/heads/foobar")
to generate a describe name "refs/heads/foobar-6-g02ac983", and we should
be able to use that name to refer to the object whose name is 02ac983.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin/checkout.c b/builtin/checkout.c
index 4ad74270cf1ae8be73372f8511f21ed1b14efdb4..88708d48bf5483a537839a2b1439af2880b1fd35 100644 (file)
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -874,7 +874,7 @@ no_reference:
                if (strbuf_check_branch_ref(&buf, opts.new_branch))
                        die("git checkout: we do not like '%s' as a branch name.",
                            opts.new_branch);
-               if (!get_sha1(buf.buf, rev)) {
+               if (ref_exists(buf.buf)) {
                        opts.branch_exists = 1;
                        if (!opts.new_branch_force)
                                die("git checkout: branch %s already exists",

diff --git a/refs.c b/refs.c
index 6f486ae62d8b4605520e75286ca36217d0715363..92cd0d14c32de85b35fff22cab3dd82e4bd2b757 100644 (file)
--- a/refs.c
+++ b/refs.c
@@ -1732,6 +1732,12 @@ int update_ref(const char *action, const char *refname,
        return 0;
 }
 
+int ref_exists(char *refname)
+{
+       unsigned char sha1[20];
+       return !!resolve_ref(refname, sha1, 1, NULL);
+}
+
 struct ref *find_ref_by_name(const struct ref *list, const char *name)
 {
        for ( ; list; list = list->next)

diff --git a/refs.h b/refs.h
index 762ce504b5eba3aacff204321a7c41db2b1e6053..070a7d9caa53f94cbbad984c3d8ae2c3fbfe7b87 100644 (file)
--- a/refs.h
+++ b/refs.h
@@ -46,6 +46,7 @@ extern void warn_dangling_symref(FILE *fp, const char *msg_fmt, const char *refn
  */
 extern void add_extra_ref(const char *refname, const unsigned char *sha1, int flags);
 extern void clear_extra_refs(void);
+extern int ref_exists(char *);
 
 extern int peel_ref(const char *, unsigned char *);
 

diff --git a/t/t2018-checkout-branch.sh b/t/t2018-checkout-branch.sh
index 1caffeac074ed9a8e434a3d6e53c20b00e8672cc..741d84257b5704b059074d5376cd10f3d358daba 100755 (executable)
--- a/t/t2018-checkout-branch.sh
+++ b/t/t2018-checkout-branch.sh
@@ -163,4 +163,15 @@ test_expect_success 'checkout -f -B to an existing branch with mergeable changes
        test_must_fail test_dirty_mergeable
 '
 
+test_expect_success 'checkout -b <describe>' '
+       git tag -f -m "First commit" initial initial &&
+       git checkout -f change1 &&
+       name=$(git describe) &&
+       git checkout -b $name &&
+       git diff --exit-code change1 &&
+       echo "refs/heads/$name" >expect &&
+       git symbolic-ref HEAD >actual &&
+       test_cmp expect actual
+'
+
 test_done