Tzadik Vanderhoof [off-list ref] writes:
On Tue, May 4, 2021 at 2:01 PM Andrew Oakley [off-list ref] wrote:
quoted
The key thing that I'm trying to point out here is that the encoding is
not necessarily consistent between different commits. The changes that
you have proposed force you to pick one encoding that will be used for
every commit. If it's wrong then data will be corrupted, and there is
no option provided to avoid that. The only way I can see to avoid this
issue is to not attempt to re-encode the data - just pass it directly
to git.
No, my "fallbackEndocing" setting is just that... a fallback. My proposal
*always* tries to decode in UTF-8 first! Only if that throws an exception
will my "fallbackEncoding" come into play, and it only comes into play
for the single changeset description that was invalid UTF-8. After that,
subsequent descriptions will again be tried in UTF-8 first.
Hmph, I do not quite see the need for "No" at the beginning of what
you said. The fallbackEncoding can specify only one non UTF-8
encoding, so even if majority of commits were in UTF-8 but when you
need to import two commits with non UTF-8 encoding, there is no
suitable value to give to the fallbackEncoding setting. One of
these two commits will fail to decode first in UTF-8 and then fail
to decode again with the fallback, and after that a corrupted
message remains.
quoted
I think another way to solve the issue you have is the encoding header
on git commits. We can pass the bytes through git-p4 unmodified, but
mark the commit message as being encoded using something that isn't
UTF-8. That avoids any potentially lossy conversions when cloning the
repository, but should allow the data to be displayed correctly in git.
Yes, that could be a solution. I will try that out.
If we can determine in what encoding the thing that came out of
Perforce is written in, we can put it on the encoding header of the
resulting commit. But if that is possible to begin with, perhaps we
do not even need to do so---if you can determine what the original
encoding is, you can reencode with that encoding into UTF-8 inside
git-p4 while creating the commit, no?
And if the raw data that came from Perforce cannot be reencoded to
UTF-8 (i.e. iconv fails to process for some reason), then whether
the translation is done at the import time (i.e. where you would
have used the fallbackEncoding to reencode into UTF-8) or at the
display time (i.e. "git show" would notice the encoding header and
try to reencode the raw data from that encoding into UTF-8), it
would fail in the same way, so I do not see much advantage in
writing the encoding header into the resulting object (other than
shifting the blame to downstream and keeping the original data
intact, which is a good design principle).
On Tue, May 4, 2021 at 6:11 PM Junio C Hamano [off-list ref] wrote:
Tzadik Vanderhoof [off-list ref] writes:
quoted
On Tue, May 4, 2021 at 2:01 PM Andrew Oakley [off-list ref] wrote:
quoted
The key thing that I'm trying to point out here is that the encoding is
not necessarily consistent between different commits. The changes that
you have proposed force you to pick one encoding that will be used for
every commit. If it's wrong then data will be corrupted, and there is
no option provided to avoid that. The only way I can see to avoid this
issue is to not attempt to re-encode the data - just pass it directly
to git.
No, my "fallbackEndocing" setting is just that... a fallback. My proposal
*always* tries to decode in UTF-8 first! Only if that throws an exception
will my "fallbackEncoding" come into play, and it only comes into play
for the single changeset description that was invalid UTF-8. After that,
subsequent descriptions will again be tried in UTF-8 first.
The fallbackEncoding can specify only one non UTF-8
encoding, so even if majority of commits were in UTF-8 but when you
need to import two commits with non UTF-8 encoding, there is no
suitable value to give to the fallbackEncoding setting. One of
these two commits will fail to decode first in UTF-8 and then fail
to decode again with the fallback, and after that a corrupted
message remains.
I'm not sure I understand your scenario. If the majority of commits
are in UTF-8, but there are 2 with the same UTF-8 encoding (say
"cp1252"), then just set "fallbackEndocing" to "cp1252" and all
the commits will display fine.
Are you talking about a scenario where most of the commits are UTF-8,
one is "cp1252" and another one is "cp1251", so a total of 3 encodings
are used in the Perforce depot? I don't think that is a common scenario.
But you have a point that my patch does not address that scenario.
If we can determine in what encoding the thing that came out of
Perforce is written in, we can put it on the encoding header of the
resulting commit. But if that is possible to begin with, perhaps we
do not even need to do so---if you can determine what the original
encoding is, you can reencode with that encoding into UTF-8 inside
git-p4 while creating the commit, no?
And if the raw data that came from Perforce cannot be reencoded to
UTF-8 (i.e. iconv fails to process for some reason), then whether
the translation is done at the import time (i.e. where you would
have used the fallbackEncoding to reencode into UTF-8) or at the
display time (i.e. "git show" would notice the encoding header and
try to reencode the raw data from that encoding into UTF-8), it
would fail in the same way, so I do not see much advantage in
writing the encoding header into the resulting object (other than
shifting the blame to downstream and keeping the original data
intact, which is a good design principle).
I agree with the idea that if you know what the encoding is, then
why not just use that knowledge to convert that to UTF-8, rather
than use the encoding header.
I'm not sure about how complete the support in "git" is for encoding
headers. Does *everything* that reads commit messages respect the
encoding header and handle it properly? The documentation seems to
discourage their use altogether and in any event, the main use case
seems to be a project where everyone has settled on the same legacy
encoding to use everywhere, which is not really the case for our situation.
If we want to abandon the "fallbackEncoding" direction, then the only other
option I see is:
Step 1) try to decode in UTF-8. If that succeeds then it is almost certain
that it really was in UTF-8 (due to the design of UTF-8). Make the commit
in UTF-8.
Step 2) If it failed to decode in UTF-8, either use heuristics to detect the
encoding, or query the OS for the current code page and assume it's that.
Then use the selected encoding to convert to UTF-8.
Only the heuristics option will satisfy the case of more than 1 encoding
(in addition to UTF-8) being present in the Perforce depot, and in any event
the current code page may not help at all.
I'm not really familiar with what encoding-detection heuristics are available
for Python and how reliable, stable or performant they are. It would also
involve taking on another library dependency.
I will take a look at the encoding-detection options out there.
Oops, noticed a typo.... the paragraph should read:
I'm not sure I understand your scenario. If the majority of commits
are in UTF-8, but there are 2 with the same *non* UTF-8 encoding (say
"cp1252"), then just set "fallbackEndocing" to "cp1252" and all
the commits will display fine.