On Sat, Nov 10, 2018 at 10:23:11PM -0800, Elijah Newren wrote: > Knowing the original names (hashes) of commits, blobs, and tags can > sometimes enable post-filtering that would otherwise be difficult or > impossible. In particular, the desire to rewrite commit messages which > refer to other prior commits (on top of whatever other filtering is > being done) is very difficult without knowing the original names of each > commit. > > This commit teaches a new --show-original-ids option to fast-export > which will make it add a 'originally <hash>' line to blob, commits, and > tags. It also teaches fast-import to parse (and ignore) such lines.
Makes sense as a feature; I think filter-branch can make its mappings available, too. Do we need to worry about compatibility with other fast-import programs? I think no, because this is not enabled by default (so if sending the extra lines to another importer hurts, the answer is "don't do that"). I have a vague feeling that there might be some way to combine this with --export-marks or --no-data, but I can't really think of a way. They seem related, but not quite. > --- > Documentation/git-fast-export.txt | 7 +++++++ > builtin/fast-export.c | 20 +++++++++++++++----- > fast-import.c | 17 +++++++++++++++++ > t/t9350-fast-export.sh | 17 +++++++++++++++++ > 4 files changed, 56 insertions(+), 5 deletions(-) The fast-import format is documented in Documentation/git-fast-import.txt. It might need an update to cover the new format. > --- a/Documentation/git-fast-export.txt > +++ b/Documentation/git-fast-export.txt > @@ -121,6 +121,13 @@ marks the same across runs. > used by a repository which already contains the necessary > parent commits. > > +--show-original-ids:: > + Add an extra directive to the output for commits and blobs, > + `originally <SHA1SUM>`. While such directives will likely be > + ignored by importers such as git-fast-import, it may be useful > + for intermediary filters (e.g. for rewriting commit messages > + which refer to older commits, or for stripping blobs by id). I'm not quite sure how a blob ends up being rewritten by fast-export (I get that commits may change due to dropping parents). The name "originally" doesn't seem great to me. Probably because I would continually wonder if it has one "l" or two. ;) Perhaps something like "original-oid" might be better. That's well into bikeshed territory, though. -Peff
