Different with-http CPP check; fix remote imports in GHCJS

[patrickmn]

I submitted #1311 before studying Import.hs carefully enough, and my GHCJS build worked perfectly (with local imports, doh!) so I didn't notice.

Since I removed the GHCJS dependency on http-client, the CPP check for MIN_VERSION_http_client no longer works. I noticed the existence of -DWITH_HTTP in the tasty test suite and added that at the library level. (I think it's clearer too.)

Also, fortunately, Manager is not actually needed in Import.hs, just the check for WITH_HTTP.

[patrickmn]

Doctest again. Revisiting tomorrow.

[sjakobi]

Looks pretty reasonable to me. I think CI with GHCJS would still be a good idea though – I could try adding a Travis job for this…

Regarding the doctests failure: AppVeyor reports:

when making flags consistent: warning:
    -O conflicts with --interactive; -O ignored.
C:\projects\dhall-haskell\dhall\src/Dhall/Tutorial.hs:447: failure in expression `input auto "https://raw.githubusercontent.com/dhall-lang/dhall-haskell/18e4e9a18dc53271146df3ccf5b4177c3552236b/examples/True" :: IO Bool'
expected: "True"
 but got: "*** Exception: "
          "\8627 https://raw.githubusercontent.com/dhall-lang/dhall-haskell/18e4e9a18dc53271146df3ccf5b4177c3552236b/examples/True"
          ""
          "\ESC[1;31mError\ESC[0m: Cannot import HTTP URL."
          ""
          "Dhall was compiled without the 'with-http' flag."
          ""
          "The requested URL was: https://raw.githubusercontent.com/dhall-lang/dhall-haskell/18e4e9a18dc53271146df3ccf5b4177c3552236b/examples/True"
          ""
          ""
          "1\9474 https://raw.githubusercontent.com/dhall-lang/dhall-haskell/18e4e9a18dc53271146df3ccf5b4177c3552236b/examples/True"
          ""
          "(input):1:1"

I suspect this can be fixed by passing -DWITH_HTTP when calling doctest in dhall/doctests/Main.hs.

[patrickmn]

Btw stuck on this trying to enter nix shell to run doctest locally:

...
5pfkp8gqca-source/pkgs/development/haskell-modules/make-package-set.nix:75:37, called from /nix/store/xz3aw1hswykigk6ivipisj5pfkp8gqca-source/pkgs/development/haskell-modules/make-package-set.nix:115:28:
while evaluating 'makeOverridable' at /nix/store/xz3aw1hswykigk6ivipisj5pfkp8gqca-source/lib/customisation.nix:72:24, called from /nix/store/xz3aw1hswykigk6ivipisj5pfkp8gqca-source/pkgs/development/haskell-modules/make-package-set.nix:98:8:
while evaluating 'drvScope' at /nix/store/xz3aw1hswykigk6ivipisj5pfkp8gqca-source/pkgs/development/haskell-modules/make-package-set.nix:88:18, called from /nix/store/xz3aw1hswykigk6ivipisj5pfkp8gqca-source/lib/customisation.nix:74:12:
moving build output '/nix/store/x8sk4h2ylq3k0xmawqh8v8bar2ljx8mg-cabal-dedupe-src' from the sandbox to the Nix store: Permission denied

[patrickmn]

Looks like that worked. Thank you :)