[PATCH v2] git checkout: create unparented branch by --orphan

[PATCH v2] git checkout: create unparented branch by --orphan

[Erick Mattos]

Similar to -b, --orphan creates a new branch, but it starts without any
commit.  After running "git checkout --orphan newbranch", you are on a
new branch "newbranch", and the first commit you create from this state
will start a new history without any ancestry.

"git checkout --orphan" keeps the index and the working tree files
intact in order to make it convenient for creating a new history whose
trees resemble the ones from the original branch.

When creating a branch whose trees have no resemblance to the ones from
the original branch, it may be easier to start work on the new branch by
untracking and removing all working tree files that came from the
original branch, by running a 'git rm -rf .' immediately after running
"checkout --orphan".

Signed-off-by: Erick Mattos <erick.mattos@gmail.com>
---

Rearragements and minor changes.

 Documentation/git-checkout.txt |   21 ++++++++++++++++-
 builtin/checkout.c             |   13 ++++++++-
 t/t2017-checkout-orphan.sh     |   50 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 81 insertions(+), 3 deletions(-)
 create mode 100755 t/t2017-checkout-orphan.sh

diff --git a/Documentation/git-checkout.txt b/Documentation/git-checkout.txt
index 37c1810..5a50997 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 <new_branch>] [<start_point>]
+'git checkout' [-q] [-f] [-m] [[-b|--orphan] <new_branch>] [<start_point>]
 'git checkout' [-f|--ours|--theirs|-m|--conflict=<style>] [<tree-ish>] [--] <paths>...
 'git checkout' --patch [<tree-ish>] [--] [<paths>...]
 
@@ -90,6 +90,25 @@ explicitly give a name with '-b' in such a case.
 	Create the new branch's reflog; see linkgit:git-branch[1] for
 	details.
 
+--orphan::
+	Create a new branch named <new_branch>, unparented to any other
+	branch.  The new branch you switch to does not have any commit
+	and after the first one it will become the root of a new history
+	completely unconnected from all the other branches.
++
+When you use "--orphan", a new unparented branch is created having the
+index and the working tree intact.  This allows you to start a new
+history that records set of paths similar to that of the start-point
+commit, which is useful when you want to keep different branches for
+different audiences you are working to like when you have an open source
+and commercial versions of a software, for example.
++
+If you want to start a disconnected history that records set of paths
+totally different from the original branch, you may want to first clear
+the index and the working tree, by running "git rm -rf ." from the
+top-level of the working tree, before preparing your files (by copying
+from elsewhere, extracting a tarball, etc.) in the working tree.
+
 -m::
 --merge::
 	When switching branches,
diff --git a/builtin/checkout.c b/builtin/checkout.c
index acefaaf..14b6d6b 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -33,6 +33,7 @@ struct checkout_opts {
 	int writeout_error;
 
 	const char *new_branch;
+	const char *new_orphan_branch;
 	int new_branch_log;
 	enum branch_track track;
 };
@@ -491,8 +492,9 @@ static void update_refs_for_switch(struct checkout_opts *opts,
 	struct strbuf msg = STRBUF_INIT;
 	const char *old_desc;
 	if (opts->new_branch) {
-		create_branch(old->name, opts->new_branch, new->name, 0,
-			      opts->new_branch_log, opts->track);
+		if (!opts->new_orphan_branch)
+			create_branch(old->name, opts->new_branch, new->name, 0,
+				      opts->new_branch_log, opts->track);
 		new->name = opts->new_branch;
 		setup_branch_path(new);
 	}
@@ -632,6 +634,7 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 		OPT_BOOLEAN('l', NULL, &opts.new_branch_log, "log for new branch"),
 		OPT_SET_INT('t', "track",  &opts.track, "track",
 			BRANCH_TRACK_EXPLICIT),
+		OPT_STRING(0, "orphan", &opts.new_orphan_branch, "new branch", "new unparented branch"),
 		OPT_SET_INT('2', "ours", &opts.writeout_stage, "stage",
 			    2),
 		OPT_SET_INT('3', "theirs", &opts.writeout_stage, "stage",
@@ -677,6 +680,12 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 		opts.new_branch = argv0 + 1;
 	}
 
+	if (opts.new_orphan_branch) {
+		if (opts.new_branch)
+			die("--orphan and -b are mutually exclusive");
+		opts.new_branch = opts.new_orphan_branch;
+	}
+
 	if (conflict_style) {
 		opts.merge = 1; /* implied */
 		git_xmerge_config("merge.conflictstyle", conflict_style, NULL);
diff --git a/t/t2017-checkout-orphan.sh b/t/t2017-checkout-orphan.sh
new file mode 100755
index 0000000..5a9a3fa
--- /dev/null
+++ b/t/t2017-checkout-orphan.sh
@@ -0,0 +1,50 @@
+#!/bin/sh
+#
+# Copyright (c) 2010 Erick Mattos
+#
+
+test_description='git checkout --orphan
+
+Main Tests for --orphan functionality.'
+
+. ./test-lib.sh
+
+TEST_FILE=foo
+
+test_expect_success 'Setup' '
+	echo "Initial" >"$TEST_FILE" &&
+	git add "$TEST_FILE" &&
+	git commit -m "First Commit"
+	test_tick &&
+	echo "State 1" >>"$TEST_FILE" &&
+	git add "$TEST_FILE" &&
+	test_tick &&
+	git commit -m "Second Commit"
+'
+
+test_expect_success '--orphan creates a new orphan branch from HEAD' '
+	git checkout --orphan alpha &&
+	test_must_fail git rev-parse --verify HEAD &&
+	test "refs/heads/alpha" = "$(git symbolic-ref HEAD)" &&
+	test_tick &&
+	git commit -m "Third Commit" &&
+	test_must_fail git rev-parse --verify HEAD^ &&
+	git diff-tree --quiet master alpha
+'
+
+test_expect_success '--orphan creates a new orphan branch from <start_point>' '
+	git checkout master &&
+	git checkout --orphan beta master^ &&
+	test_must_fail git rev-parse --verify HEAD &&
+	test "refs/heads/beta" = "$(git symbolic-ref HEAD)" &&
+	test_tick &&
+	git commit -m "Fourth Commit" &&
+	test_must_fail git rev-parse --verify HEAD^ &&
+	git diff-tree --quiet master^ beta
+'
+
+test_expect_success '--orphan must be rejected with -b' '
+	test_must_fail git checkout --orphan new -b newer
+'
+
+test_done
-- 
1.7.0.2.280.g069ed