Switch to new operation for obtaining file descriptors #20
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There is an effort to move some GHC-specific modules out of
base. Candidates for such moving areGHC.IO.Handle.TypesandGHC.IO.Handle.Internals. These modules are often used for obtaining POSIX file descriptors from Haskell handles. Such a use is also present in theterminal-sizepackage as part of the implementation of thehSizeoperation for POSIX.There is a proposal to add dedicated operations for operating-system handle acquisition to
base. A corresponding draft implementation can be found in GHC merge request !14732. The present pull request changes the implementation ofhSizeto use one of those new operations.Note that this pull request slightly changes the behavior of the POSIX version of
hSize, which previously returnedNothingwhen the given handle was not backed by a file descriptor but with the changes in this pull request throws an exception in such a situation. This actually makes the POSIX version ofhSizebehave analogous to the Windows version ofhSize, which may be considered a good thing.