checkout: introduce --{,no-}overlay option

Currently 'git checkout' is defined as an overlay operation, which
means that if in 'git checkout <tree-ish> -- [<pathspec>]' we have an
entry in the index that matches <pathspec>, but that doesn't exist in
<tree-ish>, that entry will not be removed from the index or the
working tree.

Introduce a new --{,no-}overlay option, which allows using 'git
checkout' in non-overlay mode, thus removing files from the working
tree if they do not exist in <tree-ish> but match <pathspec>.

Note that 'git checkout -p <tree-ish> -- [<pathspec>]' already works
this way, so no changes are needed for the patch mode.  We disallow
'git checkout --overlay -p' to avoid confusing users who would expect
to be able to force overlay mode in 'git checkout -p' this way.

Untracked files are not affected by this change, so 'git checkout
--no-overlay HEAD -- untracked' will not remove untracked from the
working tree.  This is so e.g. 'git checkout --no-overlay HEAD -- dir/'
doesn't delete all untracked files in dir/, but rather just resets the
state of files that are known to git.

Suggested-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 48 insertions, 0 deletions

diff --git a/t/t2025-checkout-no-overlay.sh b/t/t2025-checkout-no-overlay.sh
new file mode 100755
index 0000000000..76330cb5ab
--- /dev/null
+++ b/t/t2025-checkout-no-overlay.sh
@@ -0,0 +1,47 @@
+#!/bin/sh
+
+test_description='checkout --no-overlay <tree-ish> -- <pathspec>'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	git commit --allow-empty -m "initial"
+'
+
+test_expect_success 'checkout --no-overlay deletes files not in <tree-ish>' '
+	>file &&
+	mkdir dir &&
+	>dir/file1 &&
+	git add file dir/file1 &&
+	git checkout --no-overlay HEAD -- file &&
+	test_path_is_missing file &&
+	test_path_is_file dir/file1
+'
+
+test_expect_success 'checkout --no-overlay removing last file from directory' '
+	git checkout --no-overlay HEAD -- dir/file1 &&
+	test_path_is_missing dir
+'
+
+test_expect_success 'checkout -p --overlay is disallowed' '
+	test_must_fail git checkout -p --overlay HEAD 2>actual &&
+	test_i18ngrep "fatal: -p and --overlay are mutually exclusive" actual
+'
+
+test_expect_success '--no-overlay --theirs with D/F conflict deletes file' '
+	test_commit file1 file1 &&
+	test_commit file2 file2 &&
+	git rm --cached file1 &&
+	echo 1234 >file1 &&
+	F1=$(git rev-parse HEAD:file1) &&
+	F2=$(git rev-parse HEAD:file2) &&
+	{
+		echo "100644 $F1 1	file1" &&
+		echo "100644 $F2 2	file1"
+	} | git update-index --index-info &&
+	test_path_is_file file1 &&
+	git checkout --theirs --no-overlay -- file1 &&
+	test_path_is_missing file1
+'
+
+test_done
diff --git a/t/t9902-completion.sh b/t/t9902-completion.sh
index d01ad8eb25..5758fffa0d 100755
--- a/t/t9902-completion.sh
+++ b/t/t9902-completion.sh
@@ -1436,6 +1436,7 @@ test_expect_success 'double dash "git checkout"' '
 	--progress Z
 	--no-quiet Z
 	--no-... Z
+	--overlay Z
 	EOF
 '