fixup! filter-repo: add a --file-info-callback

Add another testcase for code coverage, and tweak the documentation a
bit more.

Author: newren

Documentation/git-filter-repo.txt

@@ -1289,12 +1289,15 @@ deletions have no file contents to operate on).  The file info
 callback takes four parameters (filename, mode, blob_id, and value),
 and expects three to be returned (filename, mode, blob_id).  The
 filename is handled similar to the filename callback; it can be used
-to rename the file, or if set to None, to drop that change from the
-commit.  The mode is a simple bytestring (or None to signal you want
-the file in question deleted; mode being None trumps filename being
-None), and the blob_id is most useful in conjunction with the value
-parameter.  The value parameter is an instance of a class that has the
-following functions
+to rename the file.  The mode is a simple bytestring (b"100644" for
+regular non-executable files, b"100755" for executable files/scripts,
+b"120000" for symlinks, and b"160000" for submodules).  For special
+cases, there are two special return values for mode and filename -- a
+mode of None signals that you want the file deleted by the commit
+processing this change, and a filename of None signals that you want
+this change dropped from the commit processing it.  The blob_id is
+most useful in conjunction with the value parameter.  The value
+parameter is an instance of a class that has the following functions
   value.get_contents_by_identifier(blob_id) -> contents (bytestring)
   value.get_size_by_identifier(blob_id) -> size_of_blob (int)
   value.insert_file_with_contents(contents) -> blob_id

git-filter-repo

@@ -1846,12 +1846,12 @@ class FilteringOptions(object):
       value.apply_replace_text(contents) -> new_contents (bytestring)
     and can read/write the following data member from the value instance:
       value.data (dict)
-    The filename return value is interpreted the same as for
-    --filename-callback (with a value of None signalling the commit
-    modification in this commit should be dropped), and mode is one of
-    b'100644', b'100755', b'120000', or b'160000' (or None to signal that the
-    file in question should be deleted by the commit processing this file
-    change).
+    
+    The filename can be used for renaming the file similar to
+    --filename-callback, and mode is one of b'100644', b'100755',
+    b'120000', or b'160000'.  There are two special case: if filename is
+    returned as None, the change will be dropped, and if mode is None, the
+    file will be deleted by the commit processing this change.
 
     For more detailed examples and explanations AND caveats, see
       https://htmlpreview.github.io/?https://github.com/newren/git-filter-repo/blob/docs/html/git-filter-repo.html#CALLBACKS
@@ -3875,6 +3875,7 @@ class RepoFilter(object):
                                      change.blob_id,
                                      self._file_info_value)
           if mode is None:
+            assert(filename is not None)
             new_change = FileChange(b'D', filename)
           elif filename is None:
             continue # Drop the FileChange from this commit

t/t9392-filter-repo-python-callback.sh

@@ -295,6 +295,43 @@ test_expect_success '--file-info-callback messing with history' '
 	)
 '
 
+test_expect_success '--file-info-callback and deletes and drops' '
+	setup file_info_deletes_drops &&
+	(
+		cd file_info_deletes_drops &&
+
+		git rm file.doc &&
+		git commit -m "Nuke doc file" &&
+
+		git filter-repo --force --file-info-callback "
+		    size = value.get_size_by_identifier(blob_id)
+		    (newname, newmode) = (filename, mode)
+		    if filename == b\"world\" and size == 12:
+		      newname = None
+		    if filename == b\"advice\" and size == 77:
+		      newmode = None
+		    return (newname, newmode, blob_id)
+                    "
+
+		cat <<-EOF >expect &&
+		foobar.c
+		secret
+		world
+		EOF
+
+		echo 1 >expect &&
+		git rev-list --count HEAD -- world >actual &&
+		test_cmp expect actual &&
+
+		echo 2 >expect &&
+		git rev-list --count HEAD -- advice >actual &&
+		test_cmp expect actual &&
+
+		echo hello >expect &&
+		test_cmp expect world
+	)
+'
+
 test_lazy_prereq UNIX2DOS '
         unix2dos -h
         test $? -ne 127