Add operations for obtaining operating-system handles

[jeltsch]

In order to decouple base versioning from GHC versioning, it is necessary to remove various GHC-specific modules from base. Among these module are GHC.IO.Handle.Types and GHC.IO.Handle.Internals. Currently, there are various packages on Hackage that use these modules. One purpose of such use is obtaining operating-system handles (file descriptors, Windows handles) that underlie Haskell handles.

GHC merge request !14732 adds a new module System.IO.OS to base, which contains several operations for obtaining operating-system handles. These new operations, together with the operation withHandleToHANDLE from the Win32 package, have been used to implement alternatives to operating-system handle acquisition based on the above-mentioned internal modules in a total of six packages on Hackage. For details, see the following respective pull requests:

• UnkindPartition/ansi-terminal#187
• haskell/haskeline#211
• jeltsch/hsshellscript#2
• haskell/process#348
• Happstack/sendfile#5
• biegunka/terminal-size#20

[hasufell]

Since I'm maintaining file-io I'd be interested in a PR/patch.

[jeltsch]

Is file-io affected by this? According to my data collection, file-io-0.1.5 has only the following uses of modules that should be internal and whose internalization carries stability risk 3, which includes GHC.IO.Handle.Types and GHC.IO.Handle.Internals:

GHC.IO.Handle.Internals

• Uses debugIO
  • Does so for automatic finalization of handles

GHC.IO.Handle.Types

• Uses Handle
  • Can be imported from System.IO
• Uses Handle’s data constructors
  • Does so for automatic finalization of handles
• Uses Handle__
  • Does so for automatic finalization of handles

GHC.IO.SubSystem

• Uses ioSubSystem in tests on Windows
  • Does so for selectively setting FILE_FLAG_OVERLAPPED
  • Can use (<!>) instead

[hasufell]

Well, you're saying that GHC.IO.Handle.Types and GHC.IO.Handle.Internals ought to be removed (although not in this proposal). So how do I future proof myself?

And what about GHC.IO.Handle.FD? Will it stay?