readFile creates new files on Windows

[Bodigrim]

Win 10, GHC 9.6.3:

$ cabal repl -b file-io 
ghci> :set -XQuasiQuotes
ghci> System.File.OsPath.readFile [System.OsPath.osp|does-not-exist|]
""

What's worse is that readFile also creates an empty does-not-exist file.

[hasufell]

Ouch.

We're using the Win32 API proper, which is a bit peculiar.

I'll look at it this weekend.

[hasufell]

From a quick glance it seems I was tricked by the posix functions behaving in a certain way:

• openFile by design creates a missing file for every IOMode except ReadOnly
• openExistingFile never creates the file
• we use openFile through withFile

The solution seems to be to use openExistingFile for all read operations. On posix it doesn't matter, on windows it does.

[hasufell]

Or we just change this

file-io/windows/System/File/Platform.hs

Line 48 in 9b1cc99

ReadMode -> Win32.oPEN_ALWAYS

to Win32.oPEN_EXISTING.

[hasufell]

This is fixed here: 9436ee8