Fix Unicode output in cabal-testsuite

[9999years]

System.Process.createPipe calls (through many intermediaries) GHC.IO.Handle.FD.fdToHandle, whose documentation says:

Makes a binary Handle. This is for historical reasons; it should
probably be a text Handle with the default encoding and newline
translation instead.

The documentation for System.IO.hSetBinaryMode says:

This has the same effect as calling hSetEncoding with char8, together
with hSetNewlineMode with noNewlineTranslation.

But this is a lie, and Unicode written to or read from binary handles is always encoded or decoded as Latin-1, which is always the wrong choice.

Therefore, we explicitly set the output to UTF-8 to keep it consistent between platforms and correct on all modern computers.

See: https://gitlab.haskell.org/ghc/ghc/-/issues/25307

---

• Patches conform to the coding conventions.
• Is this a PR that fixes CI? If so, it will need to be backported to older cabal release branches (ask maintainers for directions).

[9999years]

Note: We set LC_ALL=C in testEnv here:

cabal/cabal-testsuite/src/Test/Cabal/Monad.hs

Line 406 in c53a03a

[ ("LC_ALL", Just "C")

We might want to set GHC_NO_UNICODE=1 to avoid Unicode output entirely in some cases:

https://ghc.gitlab.haskell.org/ghc/doc/users_guide/using.html#envvar-GHC_NO_UNICODE

[ulysses4ever]

We set LC_ALL=C in testEnv

I wonder if we should drop it (or set a UTF8-based locale explicitly). It's 2024, and getting out of the way trying to avoid Unicode doesn't sound like a good idea.

[geekosaur]

This doesn't affect any test output?