fast-import: allow unquoted empty path for root

Ever since filerename was added in f39a946a1f (Support wholesale
directory renames in fast-import, 2007-07-09) and filecopy in b6f3481bb4
(Teach fast-import to recursively copy files/directories, 2007-07-15),
both have produced an error when the destination path is empty. Later,
when support for targeting the root directory with an empty string was
added in 2794ad5244 (fast-import: Allow filemodify to set the root,
2010-10-10), this had the effect of allowing the quoted empty string
(`""`), but forbidding its unquoted variant (``). This seems to have
been intended as simple data validation for parsing two paths, rather
than a syntax restriction, because it was not extended to the other
operations.

All other occurrences of paths (in filemodify, filedelete, the source of
filecopy and filerename, and ls) allow both.

For most of this feature's lifetime, the documentation has not
prescribed the use of quoted empty strings. In e5959106d6
(Documentation/fast-import: put explanation of M 040000 <dataref> "" in
context, 2011-01-15), its documentation was changed from “`<path>` may
also be an empty string (`""`) to specify the root of the tree” to “The
root of the tree can be represented by an empty string as `<path>`”.

Thus, we should assume that some front-ends have depended on this
behavior.

Remove this restriction for the destination paths of filecopy and
filerename and change tests targeting the root to test `""` and ``.

Signed-off-by: Thalia Archibald <thalia@archibald.dev>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 190 insertions, 176 deletions

diff --git a/builtin/fast-import.c b/builtin/fast-import.c
index 765429a66c..c8a1e3ef3d 100644
--- a/builtin/fast-import.c
+++ b/builtin/fast-import.c
@@ -2423,9 +2423,6 @@ static void file_change_cr(const char *p, struct branch *b, int rename)
 
 	strbuf_reset(&source);
 	parse_path_space(&source, p, &p, "source");
-
-	if (!*p)
-		die("Missing dest: %s", command_buf.buf);
 	strbuf_reset(&dest);
 	parse_path_eol(&dest, p, "dest");
 
diff --git a/t/t9300-fast-import.sh b/t/t9300-fast-import.sh
index de2f1304e8..13f98e6688 100755
--- a/t/t9300-fast-import.sh
+++ b/t/t9300-fast-import.sh
@@ -1059,30 +1059,33 @@ test_expect_success 'M: rename subdirectory to new subdirectory' '
 	compare_diff_raw expect actual
 '
 
-test_expect_success 'M: rename root to subdirectory' '
-	cat >input <<-INPUT_END &&
-	commit refs/heads/M4
-	committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
-	data <<COMMIT
-	rename root
-	COMMIT
+for root in '""' ''
+do
+	test_expect_success "M: rename root ($root) to subdirectory" '
+		cat >input <<-INPUT_END &&
+		commit refs/heads/M4
+		committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+		data <<COMMIT
+		rename root
+		COMMIT
 
-	from refs/heads/M2^0
-	R "" sub
+		from refs/heads/M2^0
+		R $root sub
 
-	INPUT_END
+		INPUT_END
 
-	cat >expect <<-EOF &&
-	:100644 100644 $oldf $oldf R100	file2/oldf	sub/file2/oldf
-	:100755 100755 $f4id $f4id R100	file4	sub/file4
-	:100755 100755 $newf $newf R100	i/am/new/to/you	sub/i/am/new/to/you
-	:100755 100755 $f6id $f6id R100	newdir/exec.sh	sub/newdir/exec.sh
-	:100644 100644 $f5id $f5id R100	newdir/interesting	sub/newdir/interesting
-	EOF
-	git fast-import <input &&
-	git diff-tree -M -r M4^ M4 >actual &&
-	compare_diff_raw expect actual
-'
+		cat >expect <<-EOF &&
+		:100644 100644 $oldf $oldf R100	file2/oldf	sub/file2/oldf
+		:100755 100755 $f4id $f4id R100	file4	sub/file4
+		:100755 100755 $newf $newf R100	i/am/new/to/you	sub/i/am/new/to/you
+		:100755 100755 $f6id $f6id R100	newdir/exec.sh	sub/newdir/exec.sh
+		:100644 100644 $f5id $f5id R100	newdir/interesting	sub/newdir/interesting
+		EOF
+		git fast-import <input &&
+		git diff-tree -M -r M4^ M4 >actual &&
+		compare_diff_raw expect actual
+	'
+done
 
 ###
 ### series N
@@ -1259,49 +1262,52 @@ test_expect_success PIPE 'N: empty directory reads as missing' '
 	test_cmp expect actual
 '
 
-test_expect_success 'N: copy root directory by tree hash' '
-	cat >expect <<-EOF &&
-	:100755 000000 $newf $zero D	file3/newf
-	:100644 000000 $oldf $zero D	file3/oldf
-	EOF
-	root=$(git rev-parse refs/heads/branch^0^{tree}) &&
-	cat >input <<-INPUT_END &&
-	commit refs/heads/N6
-	committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
-	data <<COMMIT
-	copy root directory by tree hash
-	COMMIT
+for root in '""' ''
+do
+	test_expect_success "N: copy root ($root) by tree hash" '
+		cat >expect <<-EOF &&
+		:100755 000000 $newf $zero D	file3/newf
+		:100644 000000 $oldf $zero D	file3/oldf
+		EOF
+		root_tree=$(git rev-parse refs/heads/branch^0^{tree}) &&
+		cat >input <<-INPUT_END &&
+		commit refs/heads/N6
+		committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+		data <<COMMIT
+		copy root directory by tree hash
+		COMMIT
 
-	from refs/heads/branch^0
-	M 040000 $root ""
-	INPUT_END
-	git fast-import <input &&
-	git diff-tree -C --find-copies-harder -r N4 N6 >actual &&
-	compare_diff_raw expect actual
-'
+		from refs/heads/branch^0
+		M 040000 $root_tree $root
+		INPUT_END
+		git fast-import <input &&
+		git diff-tree -C --find-copies-harder -r N4 N6 >actual &&
+		compare_diff_raw expect actual
+	'
 
-test_expect_success 'N: copy root by path' '
-	cat >expect <<-EOF &&
-	:100755 100755 $newf $newf C100	file2/newf	oldroot/file2/newf
-	:100644 100644 $oldf $oldf C100	file2/oldf	oldroot/file2/oldf
-	:100755 100755 $f4id $f4id C100	file4	oldroot/file4
-	:100755 100755 $f6id $f6id C100	newdir/exec.sh	oldroot/newdir/exec.sh
-	:100644 100644 $f5id $f5id C100	newdir/interesting	oldroot/newdir/interesting
-	EOF
-	cat >input <<-INPUT_END &&
-	commit refs/heads/N-copy-root-path
-	committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
-	data <<COMMIT
-	copy root directory by (empty) path
-	COMMIT
+	test_expect_success "N: copy root ($root) by path" '
+		cat >expect <<-EOF &&
+		:100755 100755 $newf $newf C100	file2/newf	oldroot/file2/newf
+		:100644 100644 $oldf $oldf C100	file2/oldf	oldroot/file2/oldf
+		:100755 100755 $f4id $f4id C100	file4	oldroot/file4
+		:100755 100755 $f6id $f6id C100	newdir/exec.sh	oldroot/newdir/exec.sh
+		:100644 100644 $f5id $f5id C100	newdir/interesting	oldroot/newdir/interesting
+		EOF
+		cat >input <<-INPUT_END &&
+		commit refs/heads/N-copy-root-path
+		committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+		data <<COMMIT
+		copy root directory by (empty) path
+		COMMIT
 
-	from refs/heads/branch^0
-	C "" oldroot
-	INPUT_END
-	git fast-import <input &&
-	git diff-tree -C --find-copies-harder -r branch N-copy-root-path >actual &&
-	compare_diff_raw expect actual
-'
+		from refs/heads/branch^0
+		C $root oldroot
+		INPUT_END
+		git fast-import <input &&
+		git diff-tree -C --find-copies-harder -r branch N-copy-root-path >actual &&
+		compare_diff_raw expect actual
+	'
+done
 
 test_expect_success 'N: delete directory by copying' '
 	cat >expect <<-\EOF &&
@@ -1431,98 +1437,102 @@ test_expect_success 'N: reject foo/ syntax in ls argument' '
 	INPUT_END
 '
 
-test_expect_success 'N: copy to root by id and modify' '
-	echo "hello, world" >expect.foo &&
-	echo hello >expect.bar &&
-	git fast-import <<-SETUP_END &&
-	commit refs/heads/N7
-	committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
-	data <<COMMIT
-	hello, tree
-	COMMIT
+for root in '""' ''
+do
+	test_expect_success "N: copy to root ($root) by id and modify" '
+		echo "hello, world" >expect.foo &&
+		echo hello >expect.bar &&
+		git fast-import <<-SETUP_END &&
+		commit refs/heads/N7
+		committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+		data <<COMMIT
+		hello, tree
+		COMMIT
 
-	deleteall
-	M 644 inline foo/bar
-	data <<EOF
-	hello
-	EOF
-	SETUP_END
+		deleteall
+		M 644 inline foo/bar
+		data <<EOF
+		hello
+		EOF
+		SETUP_END
 
-	tree=$(git rev-parse --verify N7:) &&
-	git fast-import <<-INPUT_END &&
-	commit refs/heads/N8
-	committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
-	data <<COMMIT
-	copy to root by id and modify
-	COMMIT
+		tree=$(git rev-parse --verify N7:) &&
+		git fast-import <<-INPUT_END &&
+		commit refs/heads/N8
+		committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+		data <<COMMIT
+		copy to root by id and modify
+		COMMIT
 
-	M 040000 $tree ""
-	M 644 inline foo/foo
-	data <<EOF
-	hello, world
-	EOF
-	INPUT_END
-	git show N8:foo/foo >actual.foo &&
-	git show N8:foo/bar >actual.bar &&
-	test_cmp expect.foo actual.foo &&
-	test_cmp expect.bar actual.bar
-'
+		M 040000 $tree $root
+		M 644 inline foo/foo
+		data <<EOF
+		hello, world
+		EOF
+		INPUT_END
+		git show N8:foo/foo >actual.foo &&
+		git show N8:foo/bar >actual.bar &&
+		test_cmp expect.foo actual.foo &&
+		test_cmp expect.bar actual.bar
+	'
 
-test_expect_success 'N: extract subtree' '
-	branch=$(git rev-parse --verify refs/heads/branch^{tree}) &&
-	cat >input <<-INPUT_END &&
-	commit refs/heads/N9
-	committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
-	data <<COMMIT
-	extract subtree branch:newdir
-	COMMIT
+	test_expect_success "N: extract subtree to the root ($root)" '
+		branch=$(git rev-parse --verify refs/heads/branch^{tree}) &&
+		cat >input <<-INPUT_END &&
+		commit refs/heads/N9
+		committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+		data <<COMMIT
+		extract subtree branch:newdir
+		COMMIT
 
-	M 040000 $branch ""
-	C "newdir" ""
-	INPUT_END
-	git fast-import <input &&
-	git diff --exit-code branch:newdir N9
-'
+		M 040000 $branch $root
+		C "newdir" $root
+		INPUT_END
+		git fast-import <input &&
+		git diff --exit-code branch:newdir N9
+	'
 
-test_expect_success 'N: modify subtree, extract it, and modify again' '
-	echo hello >expect.baz &&
-	echo hello, world >expect.qux &&
-	git fast-import <<-SETUP_END &&
-	commit refs/heads/N10
-	committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
-	data <<COMMIT
-	hello, tree
-	COMMIT
+	test_expect_success "N: modify subtree, extract it to the root ($root), and modify again" '
+		echo hello >expect.baz &&
+		echo hello, world >expect.qux &&
+		git fast-import <<-SETUP_END &&
+		commit refs/heads/N10
+		committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+		data <<COMMIT
+		hello, tree
+		COMMIT
 
-	deleteall
-	M 644 inline foo/bar/baz
-	data <<EOF
-	hello
-	EOF
-	SETUP_END
+		deleteall
+		M 644 inline foo/bar/baz
+		data <<EOF
+		hello
+		EOF
+		SETUP_END
 
-	tree=$(git rev-parse --verify N10:) &&
-	git fast-import <<-INPUT_END &&
-	commit refs/heads/N11
-	committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
-	data <<COMMIT
-	copy to root by id and modify
-	COMMIT
+		tree=$(git rev-parse --verify N10:) &&
+		git fast-import <<-INPUT_END &&
+		commit refs/heads/N11
+		committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+		data <<COMMIT
+		copy to root by id and modify
+		COMMIT
 
-	M 040000 $tree ""
-	M 100644 inline foo/bar/qux
-	data <<EOF
-	hello, world
-	EOF
-	R "foo" ""
-	C "bar/qux" "bar/quux"
-	INPUT_END
-	git show N11:bar/baz >actual.baz &&
-	git show N11:bar/qux >actual.qux &&
-	git show N11:bar/quux >actual.quux &&
-	test_cmp expect.baz actual.baz &&
-	test_cmp expect.qux actual.qux &&
-	test_cmp expect.qux actual.quux'
+		M 040000 $tree $root
+		M 100644 inline foo/bar/qux
+		data <<EOF
+		hello, world
+		EOF
+		R "foo" $root
+		C "bar/qux" "bar/quux"
+		INPUT_END
+		git show N11:bar/baz >actual.baz &&
+		git show N11:bar/qux >actual.qux &&
+		git show N11:bar/quux >actual.quux &&
+		test_cmp expect.baz actual.baz &&
+		test_cmp expect.qux actual.qux &&
+		test_cmp expect.qux actual.quux
+	'
+done
 
 ###
 ### series O
@@ -3067,6 +3077,7 @@ test_expect_success 'S: ls with garbage after sha1 must fail' '
 # There are two sorts of ways a path can be parsed, depending on whether it is
 # the last field on the line. Additionally, ls without a <dataref> has a special
 # case. Test every occurrence of <path> in the grammar against every error case.
+# Paths for the root (empty strings) are tested elsewhere.
 #
 
 #
@@ -3321,16 +3332,19 @@ test_path_eol_quoted_fail 'ls (without dataref in commit)' 'ls ' path
 ###
 # Setup is carried over from series S.
 
-test_expect_success 'T: ls root tree' '
-	sed -e "s/Z\$//" >expect <<-EOF &&
-	040000 tree $(git rev-parse S^{tree})	Z
-	EOF
-	sha1=$(git rev-parse --verify S) &&
-	git fast-import --import-marks=marks <<-EOF >actual &&
-	ls $sha1 ""
-	EOF
-	test_cmp expect actual
-'
+for root in '""' ''
+do
+	test_expect_success "T: ls root ($root) tree" '
+		sed -e "s/Z\$//" >expect <<-EOF &&
+		040000 tree $(git rev-parse S^{tree})	Z
+		EOF
+		sha1=$(git rev-parse --verify S) &&
+		git fast-import --import-marks=marks <<-EOF >actual &&
+		ls $sha1 $root
+		EOF
+		test_cmp expect actual
+	'
+done
 
 test_expect_success 'T: delete branch' '
 	git branch to-delete &&
@@ -3432,30 +3446,33 @@ test_expect_success 'U: validate directory delete result' '
 	compare_diff_raw expect actual
 '
 
-test_expect_success 'U: filedelete root succeeds' '
-	cat >input <<-INPUT_END &&
-	commit refs/heads/U
-	committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
-	data <<COMMIT
-	must succeed
-	COMMIT
-	from refs/heads/U^0
-	D ""
+for root in '""' ''
+do
+	test_expect_success "U: filedelete root ($root) succeeds" '
+		cat >input <<-INPUT_END &&
+		commit refs/heads/U-delete-root
+		committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+		data <<COMMIT
+		must succeed
+		COMMIT
+		from refs/heads/U^0
+		D $root
 
-	INPUT_END
+		INPUT_END
 
-	git fast-import <input
-'
+		git fast-import <input
+	'
 
-test_expect_success 'U: validate root delete result' '
-	cat >expect <<-EOF &&
-	:100644 000000 $f7id $ZERO_OID D	hello.c
-	EOF
+	test_expect_success "U: validate root ($root) delete result" '
+		cat >expect <<-EOF &&
+		:100644 000000 $f7id $ZERO_OID D	hello.c
+		EOF
 
-	git diff-tree -M -r U^1 U >actual &&
+		git diff-tree -M -r U U-delete-root >actual &&
 
-	compare_diff_raw expect actual
-'
+		compare_diff_raw expect actual
+	'
+done
 
 ###
 ### series V (checkpoint)