Fix IO tests

[Bodigrim]

As dicovered in #311, certain tests fail for Windows build with GHC 8.10: DeleteFile "\\\\?\\D:\\a\\bytestring\\bytestring\\tests\\qc-test-ThreadId 5": permission denied (The process cannot access the file because it is being used by another process.), emitted by System.Directory.removeFile, invoked in Properties.hs.

bytestring/tests/Properties.hs

Lines 1609 to 1616 in a83b778

	prop_read_write_file_L x = ioProperty $ do
	tid <- myThreadId
	let f = "qc-test-"++show tid
	bracket
	(do L.writeFile f x)
	(const $ do removeFile f)
	(const $ do y <- L.readFile f
	return (x==y))

It's actually amazing that these tests have worked for ages under all other platforms, because they are reference examples of lazy I/O done wrong. Clearly the file is unlinked before its content is read in full. And bracket is useless here, because there is no resource to capture. One must explicitly force evaluation of lazy bytestring before removing the file.

[vdukhovni]

It's actually amazing that these tests have worked for ages under all other platforms, because they are reference examples of lazy I/O done wrong. Clearly the file is unlinked before its content is read in full.

Of course unlinking of open files, or conversely reading open, but unlinked files is expected POSIX behaviour, so the surprise is not really so great... While Haskell prefers to prevent overlapping open for write, the underlying Unix O/S imposes no such limitations, and nothing in haskell prevents unlinking of open files, so that particular restriction is just then a feature of the Windows API.

[Bodigrim]

Ah, now it makes sense. Thanks.

[sjakobi]

Cheers! :)