On Wed, 23 Dec 2009, Greg KH wrote:
>
> They do:
> - reorg the device ids in one usb-serial driver. I took this
> now as it's a merge pressure point, and this is just a code
> move now, no functionality changed at all. It's odd that git
> didn't show this as a code move in the diffstat, I used:
> git diff -m --stat --summary
> to generate the diffstat. Should I be doing something else?
> Or is it because the code is being removed from one file and
> placed in another one?
Since the old file stays around, git doesn't consider it a rename.
Now, you can actually change that a bit. You can use -C instead of -M,
which enables copy-detection rather than just renames, and then it changes
from
drivers/usb/serial/ftdi_sio.c | 1 +
drivers/usb/serial/ftdi_sio.h | 959 +------------------------------
drivers/usb/serial/ftdi_sio_ids.h | 986 +++++++++++++++++++++++++++++++
to
drivers/usb/serial/ftdi_sio.c | 1 +
drivers/usb/serial/ftdi_sio.h | 959 +-----------
drivers/usb/serial/{ftdi_sio.h => ftdi_sio_ids.h} | 1785 ++++++++-------------
copy drivers/usb/serial/{ftdi_sio.h => ftdi_sio_ids.h} (65%)
which isn't actually any better (since while it notices the copy of the
data, it _removes_ all the code whily copying, so the total number of
lines actually goes up!).
So -M doesn't really "help" in that the diff itself does end up larger,
but at the same time it is somewhat informative in the sense that you do
see where the data comes from.
To see another facet of it all, you could also use "-B" to say that you
want to Break all old name associations if a file has changed a lot, and
then enable rename (or copy) detection, and get
drivers/usb/serial/ftdi_sio.c | 1 +
drivers/usb/serial/ftdi_sio.h | 2063 ++++++---------------
drivers/usb/serial/{ftdi_sio.h => ftdi_sio_ids.h} | 1785 +++++++------------
rewrite drivers/usb/serial/ftdi_sio.h (68%)
rename drivers/usb/serial/{ftdi_sio.h => ftdi_sio_ids.h} (65%)
which is the largest of all diffs but it shows another side of the
situation: that sio.h file has is now a "rewrite", and the end result is
substantially different from the original. So git shows it as a "rename in
place" where the diff shows up as a total delete followed by a total
addition.
As you can see, git does see that you moved data around, but since a lot
of the data also _stayed_ in the original file, the copy/break operations
really don't help. You cannot show "copy this part of this file into that
other file" as a diff.
Btw, we _do_ do the "copy this part of this file into that other file"
when you do "git blame -C", so you can now do
git blame -C drivers/usb/serial/ftdi_sio_ids.h
and it will follow the history of the lines in that file back to the
ftdi_sio.h file. So the fact that git doesn't show it in the diffs is
really because diffs always work on a whole-file basis (ie you can show a
"rename file" diff, but you can't show a "move one function or a set of
ID's from one file to another" diff.
Linus
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