1 files changed, 119 insertions, 0 deletions
diff --git a/third_party/bazel/rules_haskell/haskell/nix/default.nix b/third_party/bazel/rules_haskell/haskell/nix/default.nix
new file mode 100644
index 000000000000..d32f558625c4
--- /dev/null
+++ b/third_party/bazel/rules_haskell/haskell/nix/default.nix
@@ -0,0 +1,119 @@
+/**
+  Generate a bazel-friendly nix package containing
+  - The haskell package itself
+  - Its documentation
+  - A bazel file ready to be loaded from the `BUILD` file and containing the
+  right call to `haskell_import`
+*/
+{ runCommand, lib, writeTextDir, symlinkJoin }:
+let
+  /* Generate the BUILD file for the package */
+  genBuildFile =
+    { package_name, package, ghc }:
+    runCommand "${package_name}-BUILD" {
+      preferLocalBuild = true;
+      allowSubstitutes = false;
+      ghc_pkg = "${ghc}/bin/ghc-pkg --simple-output -v0";
+      GHC_PACKAGE_PATH = "${package}/lib/${ghc.name}/package.conf.d";
+      inherit package_name;
+    } ''
+      query_field () {
+        $ghc_pkg field ${package_name} "$@"
+      }
+
+      query_haddock () {
+        echo -n '['
+        for FIELD in $(query_field "$@"); do
+          echo -n "\"$(echo "$FIELD" | cut -d/ -f5-)*\","
+          echo -n "\"$(echo "$FIELD" | cut -d/ -f5-)/*\","
+        done
+        echo -n ']'
+      }
+
+      query_list () {
+        echo -n '['
+        for FIELD in $(query_field "$@"); do
+          echo -n '"'
+          echo -n $(echo "$FIELD" | cut -d/ -f5-)
+          echo -n '",'
+        done
+        echo -n ']'
+      }
+
+      get_deps () {
+        echo -n '['
+        for DEP in $(query_field depends); do
+          DEPNAME=$(echo $DEP | sed 's/-[0-9].*//')
+          # Because of cabal's "internal libraries", we may have a package
+          # apparently depending on itself, so we have to filter out this
+          # corner-case (see
+          # https://github.com/tweag/rules_haskell/pull/442#discussion_r219859467)
+          if [[ -n $DEPNAME && $DEPNAME != $(query_field name) ]]; then
+            echo -n "\"@hackage-$DEPNAME\","
+          fi
+        done
+        echo -n ']'
+      }
+
+      mkdir -p $out
+      cat <<EOF > $out/BUILD.bzl
+      load("@io_tweag_rules_haskell//haskell:import.bzl", haskell_import_new = "haskell_import")
+      deps_repos = $(get_deps)
+
+      def targets():
+
+          haskell_import_new(
+              name = "pkg",
+              deps = [ dep + "//:pkg" for dep in deps_repos],
+              package_id = "$(query_field id)",
+              version = "$(query_field version)",
+              package_confs = "//:package_conf",
+              haddock_interfaces = "//:interfaces",
+              haddock_html = "//:html",
+          )
+          native.filegroup(
+            name = "html",
+            srcs = native.glob($(query_haddock haddock-html), exclude_directories=1),
+          )
+          native.filegroup(
+            name = "interfaces",
+            srcs = native.glob($(query_haddock haddock-interfaces), exclude_directories=0),
+          )
+          native.filegroup(
+            name = "bin",
+            srcs = native.glob(["bin/*"]),
+          )
+          native.filegroup(
+            name = "package_conf",
+            srcs = native.glob(["lib*/${ghc.name}/package.conf.d/$(query_field name)*.conf"]),
+          )
+      EOF
+    '';
+  genAllBuilds = pkgSet:
+    let newSet =
+      lib.mapAttrs (package_name: package:
+      let
+        # Some nix packages are actually `null` because the haskell package is
+        # bundled with ghc (so it doesn't have a custom derivation of its own).
+        # For these, we simply pass the ghc derivation instead of theirs.
+        real_package = if builtins.isNull package then pkgSet.ghc else package;
+        buildFile = genBuildFile {
+          inherit (pkgSet) ghc;
+          inherit package_name;
+          package = real_package;
+        };
+      in
+      symlinkJoin {
+        name = package_name + "-bazel";
+        paths = [ real_package (real_package.doc or null) buildFile ];
+      }
+      )
+      pkgSet;
+    in
+    newSet // {
+      packageNames = writeTextDir
+        "all-haskell-packages.bzl"
+        ("packages =" + builtins.toJSON (builtins.attrNames newSet));
+    };
+in
+genAllBuilds