[Haskell-cafe] Issue building with ghc-9.8.2 and packages unix, directory, filepath and os-string

[Tom Smeding]

`os-string` has been split from `filepath` in filepath 1.5.0.0. If you 
search for "flag(os-string)" in unix' cabal file here:
   https://hackage.haskell.org/package/unix-2.8.5.1/unix.cabal
you'll see that the package has been set up to use `os-string` if 
`filepath >= 1.5.0.0`, and to not depend on `os-string` otherwise.

For filepath < 1.5.0.0, the modules in question are in the `filepath` 
package. You can get them by manually depending on `filepath` too.

If you want the post-`os-string` split `filepath`, simply add a lower 
bound on the version of `filepath` in your thing.cabal file: `filepath 
 >= 1.5.0.0`. As you can see, the diagnostic you got shows that you were 
indeed using an older `filepath` version.

- Tom

On 30/05/2024 22:22, Andrew Lelechenko wrote:
> Normally you do not need to set `constraints: unix +os-string, directory +os-string`. It’s better to let Cabal figure out a build plan without forcing its hand.
>
> Sharing your project would help, otherwise it’s hard to diagnose.
>
> Best regards,
> Andrew
>
>> On 30 May 2024, at 08:54, Daniel Trstenjak <daniel.trstenjak at gmail.com> wrote:
>>
>> Hi,
>>
>> I'm trying to get my program to compile with ghc-9.8.2. Raising the
>> upper bounds of my dependencies I'm running into a compile error
>> for the unix-2.8.5.1 package:
>>
>> [15 of 53] Compiling System.Posix.Env.PosixString ( /home/dan/sources/unix-2.8.5.1/dist-newstyle/build/x86_64-linux/ghc-9.8.2/unix-2.8.5.1/build/System/Posix/Env/PosixString.hs, /home/dan/sources/unix-2.8.5.1/dist-newstyle/build/x86_64-linux/ghc-9.8.2/unix-2.8.5.1/build/System/Posix/Env/PosixString.o, /home/dan/sources/unix-2.8.5.1/dist-newstyle/build/x86_64-linux/ghc-9.8.2/unix-2.8.5.1/build/System/Posix/Env/PosixString.dyn_o )
>>
>> System/Posix/Env/PosixString.hsc:45:1: error: [GHC-87110]
>>     Could not load module ‘System.OsString.Internal.Types’.
>>     It is a member of the hidden package ‘os-string-2.0.3’.
>>     Perhaps you need to add ‘os-string’ to the build-depends in your .cabal file.
>>     It is a member of the hidden package ‘filepath-1.4.200.1’.
>>     Perhaps you need to add ‘filepath’ to the build-depends in your .cabal file.
>>     Use -v to see a list of the files searched for.
>>    |
>> 45 | import System.OsString.Internal.Types
>>    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>>
>> System/Posix/Env/PosixString.hsc:47:1: error: [GHC-61948]
>>     Could not find module ‘System.OsString.Data.ByteString.Short’.
>>     Perhaps you meant
>>       System.OsString.Data.ByteString.Short (needs flag -package-id os-string-2.0.3)
>>       System.OsPath.Data.ByteString.Short (needs flag -package-id filepath-1.4.200.1)
>>       System.OsString.Data.ByteString.Short.Word16 (needs flag -package-id os-string-2.0.3)
>>    |
>> 47 | import qualified "os-string" System.OsString.Data.ByteString.Short as B
>>    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>>
>> System/Posix/PosixPath/FilePath.hsc:50:1: error: [GHC-61948]
>>     Could not find module ‘System.OsString.Data.ByteString.Short’.
>>     Perhaps you meant
>>       System.OsString.Data.ByteString.Short (needs flag -package-id os-string-2.0.3)
>>       System.OsPath.Data.ByteString.Short (needs flag -package-id filepath-1.4.200.1)
>>       System.OsString.Data.ByteString.Short.Word16 (needs flag -package-id os-string-2.0.3)
>>    |
>> 50 | import "os-string" System.OsString.Data.ByteString.Short as BSS
>>    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>>
>> System/Posix/PosixPath/FilePath.hsc:55:1: error: [GHC-87110]
>>     Could not load module ‘System.OsString.Internal.Types’.
>>     It is a member of the hidden package ‘os-string-2.0.3’.
>>     Perhaps you need to add ‘os-string’ to the build-depends in your .cabal file.
>>     It is a member of the hidden package ‘filepath-1.4.200.1’.
>>     Perhaps you need to add ‘filepath’ to the build-depends in your .cabal file.
>>     Use -v to see a list of the files searched for.
>>    |
>> 55 | import System.OsString.Internal.Types (PosixString(..), pattern PS)
>>    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>>
>> I can get rid of this compile error and a similar one for the directory
>> package by setting the flag os-string in my cabal.project file:
>>    constraints: unix +os-string, directory +os-string
>>
>> Now I'm wondering what is the right way to handle this case?
>> Thanks for any hints!
>>
>> Greetings,
>> Daniel
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