MetaField was already limited to alphanumerics, so it makes sense to use
Text for it.
Note that technically a UUID can contain invalid UTF-8, and so
remoteMetaDataPrefix's use of T.pack . fromUUID could replace non-UTF8
values with '?' or whatever. In practice, a UUID is usually also text,
I only kept open the possibility of it containing invalid UTF-8 to avoid
breaking parsing of strange UUIDs in git-annex branch files. So, I
decided to let this edge case slip by.
Have not updated the rest of the code base yet for this change, as the
change took 2.5 hours longer than I expected to get working properly.
As long as all code imports Utility.Aeson rather than Data.Aeson,
and no Strings that may contain utf-8 characters are used for eg, object
keys via T.pack, this is guaranteed to fix the problem everywhere that
git-annex generates json.
It's kind of annoying to need to wrap ToJSON with a ToJSON', especially
since every data type that has a ToJSON instance has to be ported over.
However, that only took 50 lines of code, which is worth it to ensure full
coverage. I initially tried an alternative approach of a newtype FileEncoded,
which had to be used everywhere a String was fed into aeson, and chasing
down all the sites would have been far too hard. Did consider creating an
intentionally overlapping instance ToJSON String, and letting ghc fail
to build anything that passed in a String, but am not sure that wouldn't
pollute some library that git-annex depends on that happens to use ToJSON
String internally.
This commit was supported by the NSF-funded DataLad project.
