[PATCH v6 2/5] branch: make create_branch() always create a branch

[Glen Choo <chooglen@google.com>]

create_branch() was formerly used to set tracking without creating a
branch. Since the previous commit replaces this use case with
dwim_and_setup_tracking(), we can simplify create_branch() so that it
always creates a branch.

Do this simplification, in particular:

* remove the special handling of BRANCH_TRACK_OVERRIDE because it is no
  longer used
* assert that clobber_head_ok can only be provided with force
* check that we're handling clobber_head_ok and force correctly by
  introducing tests for `git branch --force`

Signed-off-by: Glen Choo <chooglen@google.com>
---
 branch.c          | 55 +++++++++++++++++++++--------------------------
 branch.h          |  4 ++--
 t/t3200-branch.sh | 17 +++++++++++++++
 3 files changed, 44 insertions(+), 32 deletions(-)

diff --git a/branch.c b/branch.c
index e271a4e0a7..de680f311d 100644
--- a/branch.c
+++ b/branch.c
@@ -426,15 +426,17 @@ void create_branch(struct repository *r, const char *name,
 	char *real_ref;
 	struct strbuf ref = STRBUF_INIT;
 	int forcing = 0;
-	int dont_change_ref = 0;
-
-	if ((track == BRANCH_TRACK_OVERRIDE || clobber_head_ok)
-	    ? validate_branchname(name, &ref)
-	    : validate_new_branchname(name, &ref, force)) {
-		if (!force)
-			dont_change_ref = 1;
-		else
-			forcing = 1;
+	struct ref_transaction *transaction;
+	struct strbuf err = STRBUF_INIT;
+	char *msg;
+
+	if (clobber_head_ok && !force)
+		BUG("'clobber_head_ok' can only be used with 'force'");
+
+	if (clobber_head_ok ?
+			  validate_branchname(name, &ref) :
+			  validate_new_branchname(name, &ref, force)) {
+		forcing = 1;
 	}
 
 	dwim_branch_start(r, start_name, track, &real_ref, &oid);
@@ -442,27 +444,20 @@ void create_branch(struct repository *r, const char *name,
 	if (reflog)
 		log_all_ref_updates = LOG_REFS_NORMAL;
 
-	if (!dont_change_ref) {
-		struct ref_transaction *transaction;
-		struct strbuf err = STRBUF_INIT;
-		char *msg;
-
-		if (forcing)
-			msg = xstrfmt("branch: Reset to %s", start_name);
-		else
-			msg = xstrfmt("branch: Created from %s", start_name);
-
-		transaction = ref_transaction_begin(&err);
-		if (!transaction ||
-		    ref_transaction_update(transaction, ref.buf,
-					   &oid, forcing ? NULL : null_oid(),
-					   0, msg, &err) ||
-		    ref_transaction_commit(transaction, &err))
-			die("%s", err.buf);
-		ref_transaction_free(transaction);
-		strbuf_release(&err);
-		free(msg);
-	}
+	if (forcing)
+		msg = xstrfmt("branch: Reset to %s", start_name);
+	else
+		msg = xstrfmt("branch: Created from %s", start_name);
+	transaction = ref_transaction_begin(&err);
+	if (!transaction ||
+		ref_transaction_update(transaction, ref.buf,
+					&oid, forcing ? NULL : null_oid(),
+					0, msg, &err) ||
+		ref_transaction_commit(transaction, &err))
+		die("%s", err.buf);
+	ref_transaction_free(transaction);
+	strbuf_release(&err);
+	free(msg);
 
 	if (real_ref && track)
 		setup_tracking(ref.buf + 11, real_ref, track, quiet);
diff --git a/branch.h b/branch.h
index ab2315c611..cf3a4d3ff3 100644
--- a/branch.h
+++ b/branch.h
@@ -52,8 +52,8 @@ void dwim_and_setup_tracking(struct repository *r, const char *new_ref,
  *
  *   - force enables overwriting an existing (non-head) branch
  *
- *   - clobber_head_ok allows the currently checked out (hence existing)
- *     branch to be overwritten; without 'force', it has no effect.
+ *   - clobber_head_ok, when enabled with 'force', allows the currently
+ *     checked out (head) branch to be overwritten
  *
  *   - reflog creates a reflog for the branch
  *
diff --git a/t/t3200-branch.sh b/t/t3200-branch.sh
index 09ab132377..71a72efcb2 100755
--- a/t/t3200-branch.sh
+++ b/t/t3200-branch.sh
@@ -42,6 +42,23 @@ test_expect_success 'git branch abc should create a branch' '
 	git branch abc && test_path_is_file .git/refs/heads/abc
 '
 
+test_expect_success 'git branch abc should fail when abc exists' '
+	test_must_fail git branch abc
+'
+
+test_expect_success 'git branch --force abc should fail when abc is checked out' '
+	test_when_finished git switch main &&
+	git switch abc &&
+	test_must_fail git branch --force abc HEAD~1
+'
+
+test_expect_success 'git branch --force abc should succeed when abc exists' '
+	git rev-parse HEAD~1 >expect &&
+	git branch --force abc HEAD~1 &&
+	git rev-parse abc >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success 'git branch a/b/c should create a branch' '
 	git branch a/b/c && test_path_is_file .git/refs/heads/a/b/c
 '
-- 
2.33.GIT