[PATCH 3/3] builtin/checkout: learn -B

[Tay Ray Chuan <rctay89@gmail.com>]

Signed-off-by: Tay Ray Chuan <rctay89@gmail.com>
---
 Documentation/git-checkout.txt |   15 +++++++++++-
 builtin/checkout.c             |    7 ++++-
 t/t2018-checkout-branch.sh     |   45 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 63 insertions(+), 4 deletions(-)

diff --git a/Documentation/git-checkout.txt b/Documentation/git-checkout.txt
index 261dd90..5849e13 100644
--- a/Documentation/git-checkout.txt
+++ b/Documentation/git-checkout.txt
@@ -9,7 +9,7 @@ SYNOPSIS
 --------
 [verse]
 'git checkout' [-q] [-f] [-m] [<branch>]
-'git checkout' [-q] [-f] [-m] [[-b|--orphan] <new_branch>] [<start_point>]
+'git checkout' [-q] [-f] [-m] [[-b|-B|--orphan] <new_branch>] [<start_point>]
 'git checkout' [-f|--ours|--theirs|-m|--conflict=<style>] [<tree-ish>] [--] <paths>...
 'git checkout' --patch [<tree-ish>] [--] [<paths>...]
 
@@ -21,7 +21,7 @@ also update `HEAD` to set the specified branch as the current
 branch.
 
 'git checkout' [<branch>]::
-'git checkout' -b <new branch> [<start point>]::
+'git checkout' -b|-B <branch> [<start point>]::
 
 	This form switches branches by updating the index, working
 	tree, and HEAD to reflect the specified branch.
@@ -31,6 +31,13 @@ were called and then checked out; in this case you can
 use the `--track` or `--no-track` options, which will be passed to
 'git branch'.  As a convenience, `--track` without `-b` implies branch
 creation; see the description of `--track` below.
++
+If `-B` is given, <branch> is created if it doesn't exist; otherwise, it
+is reset. This is equivalent to
++
+------------
+$ git branch -f <branch> [<start point>] && git checkout <branch>
+------------
 
 'git checkout' [--patch] [<tree-ish>] [--] <pathspec>...::
 
@@ -75,6 +82,10 @@ entries; instead, unmerged entries are ignored.
 	Create a new branch named <new_branch> and start it at
 	<start_point>; see linkgit:git-branch[1] for details.
 
+-B::
+	Checks out to the branch named <branch>, creating it if it does
+	not exist; otherwise, the branch is reset.
+
 -t::
 --track::
 	When creating a new branch, set up "upstream" configuration. See
diff --git a/builtin/checkout.c b/builtin/checkout.c
index e794e1e..f7c2cdd 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -512,7 +512,8 @@ static void update_refs_for_switch(struct checkout_opts *opts,
 			}
 		}
 		else
-			create_branch(old->name, opts->new_branch_name, new->name, 0,
+			create_branch(old->name, opts->new_branch_name, new->name,
+				      opts->new_branch > 1,
 				      opts->new_branch_log, opts->track);
 		new->name = opts->new_branch_name;
 		setup_branch_path(new);
@@ -660,6 +661,8 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 		OPT__QUIET(&opts.quiet),
 		OPT_SET_INT('b', NULL, &opts.new_branch,
 			    "create and checkout a new branch", 1),
+		OPT_SET_INT('B', NULL, &opts.new_branch,
+			    "create and checkout a branch, resetting it if it exists", 2),
 		OPT_BOOLEAN('l', NULL, &opts.new_branch_log, "log for new branch"),
 		OPT_SET_INT('t', "track",  &opts.track, "track",
 			BRANCH_TRACK_EXPLICIT),
@@ -869,7 +872,7 @@ no_reference:
 		if (strbuf_check_branch_ref(&buf, opts.new_branch_name))
 			die("git checkout: we do not like '%s' as a branch name.",
 			    opts.new_branch_name);
-		if (!get_sha1(buf.buf, rev))
+		if (!get_sha1(buf.buf, rev) && !(opts.new_branch > 1))
 			die("git checkout: branch %s already exists", opts.new_branch_name);
 		strbuf_release(&buf);
 	}
diff --git a/t/t2018-checkout-branch.sh b/t/t2018-checkout-branch.sh
index 3c13065..1caffea 100755
--- a/t/t2018-checkout-branch.sh
+++ b/t/t2018-checkout-branch.sh
@@ -118,4 +118,49 @@ test_expect_success 'checkout -b to an existing branch fails' '
 	test_must_fail do_checkout branch2 $HEAD2
 '
 
+test_expect_success 'checkout -B to an existing branch resets branch to HEAD' '
+	git checkout branch1 &&
+
+	do_checkout branch2 "" -B
+'
+
+test_expect_success 'checkout -B to an existing branch with an explicit ref resets branch to that ref' '
+	git checkout branch1 &&
+
+	do_checkout branch2 $HEAD1 -B
+'
+
+test_expect_success 'checkout -B to an existing branch with unmergeable changes fails' '
+	git checkout branch1 &&
+
+	setup_dirty_unmergeable &&
+	test_must_fail do_checkout branch2 $HEAD1 -B &&
+	test_dirty_unmergeable
+'
+
+test_expect_success 'checkout -f -B to an existing branch with unmergeable changes discards changes' '
+	# still dirty and on branch1
+	do_checkout branch2 $HEAD1 "-f -B" &&
+	test_must_fail test_dirty_unmergeable
+'
+
+test_expect_success 'checkout -B to an existing branch preserves mergeable changes' '
+	git checkout branch1 &&
+
+	setup_dirty_mergeable &&
+	do_checkout branch2 $HEAD1 -B &&
+	test_dirty_mergeable
+'
+
+test_expect_success 'checkout -f -B to an existing branch with mergeable changes discards changes' '
+	# clean up from previous test
+	git reset --hard &&
+
+	git checkout branch1 &&
+
+	setup_dirty_mergeable &&
+	do_checkout branch2 $HEAD1 "-f -B" &&
+	test_must_fail test_dirty_mergeable
+'
+
 test_done
-- 
1.7.1.513.g4f18