fast-import: add 'ls' command

Lazy fast-import frontend authors that want to rely on the backend to
keep track of the content of the imported trees _almost_ have what
they need in the 'cat-blob' command (v1.7.4-rc0~30^2~3, 2010-11-28).
But it is not quite enough, since

 (1) cat-blob can be used to retrieve the content of files, but
     not their mode, and

 (2) using cat-blob requires the frontend to keep track of a name
     (mark number or object id) for each blob to be retrieved

Introduce an 'ls' command to complement cat-blob and take care of the
remaining needs.  The 'ls' command finds what is at a given path
within a given tree-ish (tag, commit, or tree):

	'ls' SP <dataref> SP <path> LF

or in fast-import's active commit:

	'ls' SP <path> LF

The response is a single line sent through the cat-blob channel,
imitating ls-tree output.  So for example:

	FE> ls :1 Documentation
	gfi> 040000 tree 9e6c2b599341d28a2a375f8207507e0a2a627fe9	Documentation
	FE> ls 9e6c2b599341d28a2a375f8207507e0a2a627fe9 git-fast-import.txt
	gfi> 100644 blob 4f92954396e3f0f97e75b6838a5635b583708870	git-fast-import.txt
	FE> ls :1 RelNotes
	gfi> 120000 blob b942e499449d97aeb50c73ca2bdc1c6e6d528743	RelNotes
	FE> cat-blob b942e499449d97aeb50c73ca2bdc1c6e6d528743
	gfi> b942e499449d97aeb50c73ca2bdc1c6e6d528743 blob 32
	gfi> Documentation/RelNotes/1.7.4.txt

The most interesting parts of the reply are the first word, which is
a 6-digit octal mode (regular file, executable, symlink, directory,
or submodule), and the part from the second space to the tab, which is
a <dataref> that can be used in later cat-blob, ls, and filemodify (M)
commands to refer to the content (blob, tree, or commit) at that path.

If there is nothing there, the response is "missing some/path".

The intent is for this command to be used to read files from the
active commit, so a frontend can apply patches to them, and to copy
files and directories from previous revisions.

For example, proposed updates to svn-fe use this command in place of
its internal representation of the repository directory structure.
This simplifies the frontend a great deal and means support for
resuming an import in a separate fast-import run (i.e., incremental
import) is basically free.

Signed-off-by: David Barr <david.barr@cordelta.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Improved-by: Junio C Hamano <gitster@pobox.com>
Improved-by: Sverre Rabbelier <srabbelier@gmail.com>

1 files changed, 84 insertions, 8 deletions

diff --git a/t/t9300-fast-import.sh b/t/t9300-fast-import.sh
index 52ac0e56dc..6b1ba6c858 100755
--- a/t/t9300-fast-import.sh
+++ b/t/t9300-fast-import.sh
@@ -42,6 +42,14 @@ echo "$@"'
 
 >empty
 
+test_expect_success 'setup: have pipes?' '
+	rm -f frob &&
+	if mkfifo frob
+	then
+		test_set_prereq PIPE
+	fi
+'
+
 ###
 ### series A
 ###
@@ -898,6 +906,77 @@ test_expect_success \
 	 git diff-tree -C --find-copies-harder -r N4^ N4 >actual &&
 	 compare_diff_raw expect actual'
 
+test_expect_success PIPE 'N: read and copy directory' '
+	cat >expect <<-\EOF
+	:100755 100755 f1fb5da718392694d0076d677d6d0e364c79b0bc f1fb5da718392694d0076d677d6d0e364c79b0bc C100	file2/newf	file3/newf
+	:100644 100644 7123f7f44e39be127c5eb701e5968176ee9d78b1 7123f7f44e39be127c5eb701e5968176ee9d78b1 C100	file2/oldf	file3/oldf
+	EOF
+	git update-ref -d refs/heads/N4 &&
+	rm -f backflow &&
+	mkfifo backflow &&
+	(
+		exec <backflow &&
+		cat <<-EOF &&
+		commit refs/heads/N4
+		committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+		data <<COMMIT
+		copy by tree hash, part 2
+		COMMIT
+
+		from refs/heads/branch^0
+		ls "file2"
+		EOF
+		read mode type tree filename &&
+		echo "M 040000 $tree file3"
+	) |
+	git fast-import --cat-blob-fd=3 3>backflow &&
+	git diff-tree -C --find-copies-harder -r N4^ N4 >actual &&
+	compare_diff_raw expect actual
+'
+
+test_expect_success PIPE 'N: empty directory reads as missing' '
+	cat <<-\EOF >expect &&
+	OBJNAME
+	:000000 100644 OBJNAME OBJNAME A	unrelated
+	EOF
+	echo "missing src" >expect.response &&
+	git update-ref -d refs/heads/read-empty &&
+	rm -f backflow &&
+	mkfifo backflow &&
+	(
+		exec <backflow &&
+		cat <<-EOF &&
+		commit refs/heads/read-empty
+		committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+		data <<COMMIT
+		read "empty" (missing) directory
+		COMMIT
+
+		M 100644 inline src/greeting
+		data <<BLOB
+		hello
+		BLOB
+		C src/greeting dst1/non-greeting
+		C src/greeting unrelated
+		# leave behind "empty" src directory
+		D src/greeting
+		ls "src"
+		EOF
+		read -r line &&
+		printf "%s\n" "$line" >response &&
+		cat <<-\EOF
+		D dst1
+		D dst2
+		EOF
+	) |
+	git fast-import --cat-blob-fd=3 3>backflow &&
+	test_cmp expect.response response &&
+	git rev-list read-empty |
+	git diff-tree -r --root --stdin |
+	sed "s/$_x40/OBJNAME/g" >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success \
 	'N: copy root directory by tree hash' \
 	'cat >expect <<-\EOF &&
@@ -1861,6 +1940,11 @@ test_expect_success 'R: feature no-relative-marks should be honoured' '
     test_cmp marks.new non-relative.out
 '
 
+test_expect_success 'R: feature ls supported' '
+	echo "feature ls" |
+	git fast-import
+'
+
 test_expect_success 'R: feature cat-blob supported' '
 	echo "feature cat-blob" |
 	git fast-import
@@ -1986,14 +2070,6 @@ test_expect_success 'R: print two blobs to stdout' '
 	test_cmp expect actual
 '
 
-test_expect_success 'setup: have pipes?' '
-	rm -f frob &&
-	if mkfifo frob
-	then
-		test_set_prereq PIPE
-	fi
-'
-
 test_expect_success PIPE 'R: copy using cat-file' '
 	expect_id=$(git hash-object big) &&
 	expect_len=$(wc -c <big) &&