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Frequently Asked Questions

  1. Why does ob run hang in firefox?
  2. How do I declare a new Haskell dependency?
  3. How do I add or override Haskell dependencies in the package set?
  4. How do I extend my Obelisk application with more local packages?
  5. How do I use ob run over HTTPS?
  6. How do I fix invalid entitlements?
  7. ob thunk update or ob deploy update fails
  8. How do I fix Ambiguous module name errors?
  9. How do I fix no C compiler provided for this platform errors?
  10. Names of some variables in all.js (produced by GHCJS) collide with already existing static JS files in my project
  11. How do I fix systemd-timesyncd causing my deployment to fail?
  12. How do I cache individual build components with Nix?

How do I declare a new Haskell dependency?

Every component of your Obelisk application is a standard cabal package. That means declaring new Haskell dependencies simply involves updating the build-depends field in the appropriate cabal file (backend.cabal for example). By default, Obelisk will use its curated package set to choose which version of each package you get. It's possible that the package you need is not already in the curated set or the curated version isn't the one you want. See How do I add or override Haskell dependencies in the package set? for a solution to this.

How do I add or override Haskell dependencies in the package set?

To add a Haskell package that doesn't exist in Obelisk's package set or to override the version of a package, use the overrides attribute in your project's default.nix. For example, to use a specific version of the aeson package fetched from GitHub and a specific version of the waargonaut package fetched from Hackage, your default.nix will look like:

# ...
project ./. ({ pkgs, ... }: {
# ...
  overrides = self: super: let
    aesonSrc = pkgs.fetchFromGitHub {
      owner = "obsidiansystems";
      repo = "aeson-gadt-th";
      rev = "ed573c2cccf54d72aa6279026752a3fecf9c1383";
      sha256 = "08q6rnz7w9pn76jkrafig6f50yd0f77z48rk2z5iyyl2jbhcbhx3";
    };
  in
  {
    aeson = self.callCabal2nix "aeson" aesonSrc {};
    waargonaut = self.callHackageDirect {
      pkg = "waargonaut";
      ver = "0.8.0.1";
      sha256 = "1zv28np3k3hg378vqm89v802xr0g8cwk7gy3mr77xrzy5jbgpa39";
    } {};
  };
# ...

For further information see the Haskell section of nixpkgs "Contributors Guide".

How do I extend my Obelisk application with more local packages?

If the standard packages (frontend, backend, and common) are not enough, you may add more local packages by defining them with the packages attribute in your default.nix. The sources of these packages will be automatically loaded by ob run/ob repl/etc.

# ...
project ./. ({ pkgs, ... }: {
# ...
  packages = {
    another = ./dep/another;
  };
# ...

How do I use ob run over HTTPS?

To run your app locally over HTTPS, update the protocol in config/common/route to https, and then use ob run as normal.

Obelisk generates a self-signed certificate for running HTTPS so the browser will issue a warning about using an invalid certificate. On Chrome, you can go to chrome://flags/#allow-insecure-localhost to enable invalid certificates for localhost.

How do I fix invalid entitlements?

You probably did not set ios.bundleIdentifier correctly in default.nix. When this happens you'll see an error something like this:

2018-11-25 09:34:22.438 ios-deploy[58106:8521046] [ !! ] Error 0xe8008016: The executable was signed with invalid entitlements. AMDeviceSecureInstallApplication(0, device, url, options, install_callback, 0)

Fixing the value of ios.bundleIdentifier should fix the error.

ob thunk update or ob deploy update fails

Whenever an ob command fails, try re-running it with -v.

If you're using a private repo, and you get a failure in nix-prefetch-url, you may need to unpack and repack the thunk. Here's some example output that shows this issue:

Starting Obelisk </nix/store/j8wls8a89xr6s1a47lg6g83gnbdrfd0l-obelisk-command-0.1/bin/.ob-wrapped> args=["deploy","update","-v"] logging-level=Debug
Creating process: 'nix-build' './.obelisk/impl' '-A' 'command' '--no-out-link'
✔ Built  on ./.obelisk/impl [command]
Handing off to /nix/store/j8wls8a89xr6s1a47lg6g83gnbdrfd0l-obelisk-command-0.1/bin/ob
Starting Obelisk </nix/store/j8wls8a89xr6s1a47lg6g83gnbdrfd0l-obelisk-command-0.1/bin/.ob-wrapped> args=["--no-handoff","deploy","update","-v"] logging-level=Debug
Creating process: 'git' 'ls-remote' '--exit-code' '--symref' 'https://github.com/obsidiansystems/some-private-repo.git' 'refs/heads/master'
git ls-remote maps: (fromList [],fromList [(GitRef_Branch "master","8546dfc8be9653f20bb26214e0991dbb957cb290")])
Latest commit in branch master from remote repo https://github.com/obsidiansystems/some-private-repo.git is 8546dfc8be9653f20bb26214e0991dbb957cb290
Creating process: 'nix-prefetch-url' '--unpack' '--type' 'sha256' 'https://github.com/obsidiansystems/some-private-repo/archive/8546dfc8be9653f20bb26214e0991dbb957cb290.tar.gz'
error: unable to download 'https://github.com/obsidiansystems/some-private-repo/archive/8546dfc8be9653f20bb26214e0991dbb957cb290.tar.gz': HTTP error 404
Process exited with code 1; 'nix-prefetch-url' '--unpack' '--type' 'sha256' 'https://github.com/obsidiansystems/some-private-repo/archive/8546dfc8be9653f20bb26214e0991dbb957cb290.tar.gz'
nix-prefetch-url: Failed to determine sha256 hash of URL https://github.com/obsidiansystems/some-private-repo/archive/8546dfc8be9653f20bb26214e0991dbb957cb290.tar.gz
✖ Updating thunk ./src to latest

And here's how you can fix it:

ob thunk unpack $SOME_THUNK
ob thunk pack $SOME_THUNK

Substitute the directory of your thunk for $SOME_THUNK. In the case of ob deploy update, $SOME_THUNK will be src in the deployment directory.

(Based on issue #351).

How do I fix Ambiguous module name errors?

Since obelisk places the common/backend/frontend modules packages into the same ghci, and ghci doesn't "sandbox" them, it is possible to have conflicting module errors inside ob repl/watch/run that do not appear when doing a cabal build.

You can disambiguate this via PackageImports. For instance, if you see

error:
    Ambiguous module name ‘Crypto.Hash’:
      it was found in multiple packages:
      cryptohash-0.11.9 cryptonite-0.25

then specify the package you want in the import, e.g: import "cryptonite" Crypto.Hash

How do I fix no C compiler provided for this platform errors?

This can show up when when doing nix-build (ie for deployment).

This is probably because you have a package that needs a C compiler (like snap-core) in your common or frontend modules which need to be built for ghcjs which does not in fact have a C compiler. You'll need to remove those packages from your cabal files and rework your app to not need them in the frontend.

Names of some variables in all.js (produced by GHCJS) collide with already existing static JS files in my project

Obelisk now allows the addition of a file to resolve such name collision errors. The file's path can be passed in the configuration via the externjs key, as shown below:

project ./. ({ pkgs, hackGet, ... }: with pkgs.haskell.lib; {
  staticFiles = ...
  externjs = path/to/file
})

This file should have declarations for the global variables that are needed by your static JS files, for example:

var require = false;
var lib = false;

Any variables defined in this file will not be used in the minification process.

Why does ob run hang in firefox?

ob run runs the project frontend through the jsaddle library, instead of compiling it to javascript. There is an issue with the way that jsaddle interfaces with the browser which causes ob run to fail to operate on some browsers. For more information, see this issue.

How do I fix systemd-timesyncd causing my deployment to fail?

This is an upstream issue that can be resolved by deleting /var/lib/systemd/timesync and /var/lib/private on the machine targeted for deployment, as per issue #670.

How do I cache individual build components with Nix?

I can do nix-build -A exe and the result will come completely from cache. But if I follow that up with nix-build -A ghc.backend or nix-build -A ghc.frontend and the result is not cached. Shouldn't the former have already built the latter?

The succinct answer is that ghc.backend is not statically linked and ghc.frontend is not a GHCJS build. Additionally ghcjs.frontend is not closure compiled, so the derivations are not the same and will result in a new build being triggered.

Our recommendation is to have a nix file in your project, such as release.nix, that lists all of the attributes you'd like to cache.

For example, you could do something like:

{ }:
let
  myProject = import ./. {};
in {
  android = myProject.android.frontend; # Android application
  exe = myProject.exe;                  # Compiled backend and ghcjs frontend
  shell = myProject.shells.ghc;         # Project shell
}

This gives you direct control over what's built and cached.

To see what else can be added to this list, run nix repl in your project directory and type: a = import ./. {} then look at the value of a via TAB completion to see the components of your obelisk project.