filepath: exporting `isWindows` breaks hlint

[rimmington]

Using GHCJS with Stack like so:

resolver: lts-3.9
compiler: ghcjs-0.2.0.20151230.3_ghc-7.10.2
compiler-check: match-exact
setup-info:
  ghcjs:
    source:
      ghcjs-0.2.0.20151230.3_ghc-7.10.2:
        url: "https://github.com/nrolland/ghcjs/releases/download/v.0.2.0.20151230.3/ghcjs-0.2.0.20151230.3.tar.gz"

I cannot install hlint. It looks like the filepath patch is additionally exporting isWindows, which causes the following error:

    Configuring hlint-1.9.21...
    Building hlint-1.9.21...
    Preprocessing library hlint-1.9.21...
    [ 1 of 45] Compiling Test.Util        ( src/Test/Util.hs, .stack-work/dist/x86_64-linux/Cabal-1.22.4.0_ghcjs/build/Test/Util.js_o )
    [ 2 of 45] Compiling Test.InputOutput ( src/Test/InputOutput.hs, .stack-work/dist/x86_64-linux/Cabal-1.22.4.0_ghcjs/build/Test/InputOutput.js_o )
    [ 3 of 45] Compiling HSE.Type         ( src/HSE/Type.hs, .stack-work/dist/x86_64-linux/Cabal-1.22.4.0_ghcjs/build/HSE/Type.js_o )
    [ 4 of 45] Compiling HSE.FreeVars     ( src/HSE/FreeVars.hs, .stack-work/dist/x86_64-linux/Cabal-1.22.4.0_ghcjs/build/HSE/FreeVars.js_o )
    [ 5 of 45] Compiling HSE.Util         ( src/HSE/Util.hs, .stack-work/dist/x86_64-linux/Cabal-1.22.4.0_ghcjs/build/HSE/Util.js_o )
    [ 6 of 45] Compiling HSE.Match        ( src/HSE/Match.hs, .stack-work/dist/x86_64-linux/Cabal-1.22.4.0_ghcjs/build/HSE/Match.js_o )
    [ 7 of 45] Compiling HSE.Scope        ( src/HSE/Scope.hs, .stack-work/dist/x86_64-linux/Cabal-1.22.4.0_ghcjs/build/HSE/Scope.js_o )
    [ 8 of 45] Compiling HsColour         ( src/HsColour.hs, .stack-work/dist/x86_64-linux/Cabal-1.22.4.0_ghcjs/build/HsColour.js_o )
    [ 9 of 45] Compiling Parallel         ( src/Parallel.hs, .stack-work/dist/x86_64-linux/Cabal-1.22.4.0_ghcjs/build/Parallel.js_o )
    [10 of 45] Compiling Paths_hlint      ( .stack-work/dist/x86_64-linux/Cabal-1.22.4.0_ghcjs/build/autogen/Paths_hlint.hs, .stack-work/dist/x86_64-linux/Cabal-1.22.4.0_ghcjs/build/Paths_hlint.js_o )
    [11 of 45] Compiling Util             ( src/Util.hs, .stack-work/dist/x86_64-linux/Cabal-1.22.4.0_ghcjs/build/Util.js_o )
    [12 of 45] Compiling CmdLine          ( src/CmdLine.hs, .stack-work/dist/x86_64-linux/Cabal-1.22.4.0_ghcjs/build/CmdLine.js_o )

    /tmp/stack24478/hlint-1.9.21/src/CmdLine.hs:67:12:
        Ambiguous occurrence ‘isWindows’
        It could refer to either ‘System.FilePath.isWindows’,
                                 imported from ‘System.FilePath’ at src/CmdLine.hs:13:1-22
                                 (and originally defined in ‘System.FilePath.Current’)
                              or ‘System.Info.Extra.isWindows’,
                                 imported from ‘System.Info.Extra’ at src/CmdLine.hs:18:1-24```

[benjamin-hodgson]

I've hit this issue too, when trying to build Idris. The Idris package has its own internal isWindows utility, and later it's used in a module which also imports System.FilePath.

I'll ask the Idris devs whether they mind addressing the issue once-off (by importing only the required names from System.FilePath) but as Neil Mitchell points out it's probably better for GHCJS not to patch System.FilePath's exported names.

What's isWindows used for? Would you be open to a pull request to move it to somewhere internal to GHCJS?