Linus Torvalds wrote:
On Wed, 18 Apr 2007, Rogan Dawes wrote:
Or similarly, when checking an "ODF" file in, the attribute would lead to an
appropriate script creating the "tree" of individual files.
Does this sound workable?
I think it sounds very interesting, and I'd much rather do _those_ kinds
of rewrites than keyword unexpansion. And yes, some kind of generic
support for rewriting might give people effectively the keywords they want
(I think the CVS semantics are not likely to be logical, but people can
probably do something that works for them), and at that point maybe the
keyword discussion goes away too.
However, I don't know if it is "workable".
The thing is, it's easy enough (although potentially _very_ expensive) to
run some per-file script at each commit and at each checkout. But there
are some fundamental operations that are even more common:
- checking for "file changed", aka the "git status" kind of thing
Anything we do would have to follow the same "stat" rules, at a
minimum. You can *not* afford to have to check the file manually.
So especially if you combine several pieces into one, or split one file
into several pieces, your index would have to contain the entry
that matches the _filesystem_ (because that's what the index is all
about), but then the *tree* would contain the pieces (or the single
entry that matches several filesystem entries).
Right. I would imagine that the script would have to take care of
setting timestamps in the filesystem appropriately, as well as passing
them back to git when queried.
e.g. expanding test.odf/: (since we store it as a directory)
git calls "odf.sh checkout test.odf/ <sha1> <perms> <stat>"
odf checkout calls back into git to find out the details of the files
under test.odf/, and creates a zip file containing the individual files,
with appropriate timestamps.
User then opens the file using OO.o or whatever, makes some changes and
saves the file.
The user then runs git status:
git calls "odf.sh stat test.odf/" (again, triggered by an attribute)
odf.sh does the equivalent of "zip -l" to get up to date stat info for
the component files, and passes it back to git (via stdout?)
User commits his changes:
git calls "odf.sh checkin test.odf/"
odf.sh unpacks the individual files, calls back into git to create
individual objects (using a fast-import-alike protocol over stdout?)
- what about diffs (once the stat information says something has
potentially changed)? You'd have to script those too, and it really
sounds like some very basic operations get a _lot_ more expensive and
complex.
>
This is also related to the above: one of the most fundamental diffs is
the diff of the index and a tree - so if the index matches the
"filesystem state" and the trees contain some "combined entry" or
"split entry", you'd have to teach some very core diff functionality
about that kind of mapping.
In other words, I think it's too complicated. Not necessarily impossible,
but likely harder and more complex than it's really worth.
Having a 1:1 file mapping (like the CRLF<->LF object mapping is) is a lot
easier. You just have to make sure that the index has the *stat*
information from the filesystem, but the *sha1* identity information from
the git internal format, and things automatically just fall out right. But
if you have anything but a 1:1 relationship, it gets hugely more complex.
Linus
Absolutely. I just raised it now since it was originally mentioned quite
a long time ago as a possible feature of git, and I couldn't see how it
might work.
Thanks for your time,
Rogan
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