[PATCH/RFC] Teach fast-import to import subtrees named by tree id

[Jonathan Nieder <jrnieder@gmail.com>]

To simulate the svn cp command, it would be very useful to be
replace an arbitrary file in the current revision by an
arbitrary directory from a previous one.  Modify the filemodify
command to allow that:

 M 040000 <tree id> pathname

This would be most useful in combination with a facility to
print the commit ids for new revisions as they are written.

Cc: Shawn O. Pearce <spearce@spearce.org>
Cc: Sverre Rabbelier <srabbelier@gmail.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
---
I actually thought fast-import already did this until David
mentioned that no, it does not.  Well, live and learn.

This and Sverre’s --print-marks command would allow svn-fe
to be simplified a great deal.

I was not sure whether to add a "feature" specification for
this, so I’ll try that as a separate patch.

Thoughts?
Jonathan

 Documentation/git-fast-import.txt |    8 ++++-
 fast-import.c                     |   24 ++++++++++------
 t/t9300-fast-import.sh            |   54 +++++++++++++++++++++++++++++++++++++
 3 files changed, 75 insertions(+), 11 deletions(-)

diff --git a/Documentation/git-fast-import.txt b/Documentation/git-fast-import.txt
index 19082b0..f4d9aeb 100644
--- a/Documentation/git-fast-import.txt
+++ b/Documentation/git-fast-import.txt
@@ -482,9 +482,11 @@ External data format::
 	'M' SP <mode> SP <dataref> SP <path> LF
 ....
 +
-Here `<dataref>` can be either a mark reference (`:<idnum>`)
+Here usually `<dataref>` must be either a mark reference (`:<idnum>`)
 set by a prior `blob` command, or a full 40-byte SHA-1 of an
-existing Git blob object.
+existing Git blob object.  If `<mode>` is `040000`` then
+`<dataref>` must be the full 40-byte SHA-1 of an existing
+Git tree object or a mark reference set with `--import-marks`.
 
 Inline data format::
 	The data content for the file has not been supplied yet.
@@ -509,6 +511,8 @@ in octal.  Git only supports the following modes:
 * `160000`: A gitlink, SHA-1 of the object refers to a commit in
   another repository. Git links can only be specified by SHA or through
   a commit mark. They are used to implement submodules.
+* `040000`: A subdirectory.  Subdirectories can only be specified by
+  SHA or through a tree mark set with `--import-marks`.
 
 In both formats `<path>` is the complete path of the file to be added
 (if not already existing) or modified (if already existing).
diff --git a/fast-import.c b/fast-import.c
index 1e5d66e..ad6843a 100644
--- a/fast-import.c
+++ b/fast-import.c
@@ -2131,6 +2131,7 @@ static void file_change_m(struct branch *b)
 	case S_IFREG | 0644:
 	case S_IFREG | 0755:
 	case S_IFLNK:
+	case S_IFDIR:
 	case S_IFGITLINK:
 		/* ok */
 		break;
@@ -2176,23 +2177,28 @@ static void file_change_m(struct branch *b)
 		 * another repository.
 		 */
 	} else if (inline_data) {
+		if (S_ISDIR(mode))
+			die("Directories cannot be specified 'inline': %s",
+				command_buf.buf);
 		if (p != uq.buf) {
 			strbuf_addstr(&uq, p);
 			p = uq.buf;
 		}
 		read_next_command();
 		parse_and_store_blob(&last_blob, sha1, 0);
-	} else if (oe) {
-		if (oe->type != OBJ_BLOB)
-			die("Not a blob (actually a %s): %s",
-				typename(oe->type), command_buf.buf);
 	} else {
-		enum object_type type = sha1_object_info(sha1, NULL);
+		enum object_type expected = S_ISDIR(mode) ?
+						OBJ_TREE: OBJ_BLOB;
+		enum object_type type = oe ? oe->type :
+					sha1_object_info(sha1, NULL);
 		if (type < 0)
-			die("Blob not found: %s", command_buf.buf);
-		if (type != OBJ_BLOB)
-			die("Not a blob (actually a %s): %s",
-			    typename(type), command_buf.buf);
+			die("%s not found: %s",
+					S_ISDIR(mode) ?  "Tree" : "Blob",
+					command_buf.buf);
+		if (type != expected)
+			die("Not a %s (actually a %s): %s",
+				typename(expected), typename(type),
+				command_buf.buf);
 	}
 
 	tree_content_set(&b->branch_tree, p, sha1, mode, NULL);
diff --git a/t/t9300-fast-import.sh b/t/t9300-fast-import.sh
index 131f032..50d5913 100755
--- a/t/t9300-fast-import.sh
+++ b/t/t9300-fast-import.sh
@@ -796,6 +796,60 @@ test_expect_success \
 	'git fast-import <input &&
 	 test `git rev-parse N2^{tree}` = `git rev-parse N3^{tree}`'
 
+test_expect_success \
+	'N: copy directory by id' \
+	'cat >expect <<-\EOF &&
+	:100755 100755 f1fb5da718392694d0076d677d6d0e364c79b0bc f1fb5da718392694d0076d677d6d0e364c79b0bc C100	file2/newf	file3/newf
+	:100644 100644 7123f7f44e39be127c5eb701e5968176ee9d78b1 7123f7f44e39be127c5eb701e5968176ee9d78b1 C100	file2/oldf	file3/oldf
+	EOF
+	 subdir=$(git rev-parse refs/heads/branch^0:file2) &&
+	 cat >input <<-INPUT_END &&
+	commit refs/heads/N4
+	committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+	data <<COMMIT
+	copy by tree hash
+	COMMIT
+
+	from refs/heads/branch^0
+	M 040000 $subdir file3
+	INPUT_END
+	 git fast-import <input &&
+	 git diff-tree -C --find-copies-harder -r N4^ N4 >actual &&
+	 compare_diff_raw expect actual'
+
+test_expect_success \
+	'N: modify copied tree' \
+	'cat >expect <<-\EOF &&
+	:100644 100644 fcf778cda181eaa1cbc9e9ce3a2e15ee9f9fe791 fcf778cda181eaa1cbc9e9ce3a2e15ee9f9fe791 C100	newdir/interesting	file3/file5
+	:100755 100755 f1fb5da718392694d0076d677d6d0e364c79b0bc f1fb5da718392694d0076d677d6d0e364c79b0bc C100	file2/newf	file3/newf
+	:100644 100644 7123f7f44e39be127c5eb701e5968176ee9d78b1 7123f7f44e39be127c5eb701e5968176ee9d78b1 C100	file2/oldf	file3/oldf
+	EOF
+	 subdir=$(git rev-parse refs/heads/branch^0:file2) &&
+	 cat >input <<-INPUT_END &&
+	commit refs/heads/N5
+	committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+	data <<COMMIT
+	copy by tree hash
+	COMMIT
+
+	from refs/heads/branch^0
+	M 040000 $subdir file3
+
+	commit refs/heads/N5
+	committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+	data <<COMMIT
+	modify directory copy
+	COMMIT
+
+	M 644 inline file3/file5
+	data <<EOF
+	$file5_data
+	EOF
+	INPUT_END
+	 git fast-import <input &&
+	 git diff-tree -C --find-copies-harder -r N5^^ N5 >actual &&
+	 compare_diff_raw expect actual'
+
 ###
 ### series O
 ###
-- 
1.7.1.1