nixpkgs/pkgs/development/compilers/ghcjs-ng/README.md

New build system for GHCJS 8.2

ghcjs-8.2 reworked the build system, and now comes with its own small package set of dependencies. This involves autogenerating several sources and cabal files, based on a GHC checkout. callCabal2nix is off limits, since we don't like "import from derivation" in nixpkgs. So there is a derivation that builds the nix expression that should be checked in whenever GHCJS is updated.

Updating

$ nix-prefetch-git https://github.com/ghcjs/ghcjs --rev refs/heads/ghc-8.2 \
  | jq '{ url, rev, fetchSubmodules, sha256 }' \
  > 8.2/git.json
$ cat $(nix-build ../../../.. -A haskell.compiler.ghcjs82.genStage0 --no-out-link) > 8.2/stage0.nix