3 files changed, 99 insertions, 0 deletions
diff --git a/nixpkgs/pkgs/build-support/dhall/directory-to-nix.nix b/nixpkgs/pkgs/build-support/dhall/directory-to-nix.nix
new file mode 100644
index 000000000000..d751e19df3fc
--- /dev/null
+++ b/nixpkgs/pkgs/build-support/dhall/directory-to-nix.nix
@@ -0,0 +1,25 @@
+{ dhallPackages, dhallPackageToNix}:
+
+# `dhallDirectoryToNix is a utility function to take a directory of Dhall files
+# and read them in as a Nix expression.
+#
+# This function is similar to `dhallToNix`, but takes a Nixpkgs Dhall package
+# as input instead of raw Dhall code.
+#
+# Note that this uses "import from derivation" (IFD), meaning that Nix will
+# perform a build during the evaluation phase if you use this
+# `dhallDirectoryToNix` utility.  It is not possible to use
+# `dhallDirectoryToNix` in Nixpkgs, since the Nixpkgs Hydra doesn't allow IFD.
+
+{ src
+, # The file to import, relative to the src root directory
+  file ? "package.dhall"
+}@args:
+
+let
+  generatedPkg = dhallPackages.generateDhallDirectoryPackage args;
+
+  builtPkg = dhallPackages.callPackage generatedPkg { };
+
+in
+  dhallPackageToNix builtPkg
diff --git a/nixpkgs/pkgs/build-support/dhall/package-to-nix.nix b/nixpkgs/pkgs/build-support/dhall/package-to-nix.nix
new file mode 100644
index 000000000000..301501ad49df
--- /dev/null
+++ b/nixpkgs/pkgs/build-support/dhall/package-to-nix.nix
@@ -0,0 +1,36 @@
+
+# `dhallPackageToNix` is a utility function to take a Nixpkgs Dhall package
+# (created with a function like `dhallPackages.buildDhallDirectoryPackage`)
+# and read it in as a Nix expression.
+#
+# This function is similar to `dhallToNix`, but takes a Nixpkgs Dhall package
+# as input instead of raw Dhall code.
+#
+# Note that this uses "import from derivation" (IFD), meaning that Nix will
+# perform a build during the evaluation phase if you use this
+# `dhallPackageToNix` utility.  It is not possible to use `dhallPackageToNix`
+# in Nixpkgs, since the Nixpkgs Hydra doesn't allow IFD.
+
+{ stdenv, dhall-nix }:
+
+dhallPackage:
+  let
+    drv = stdenv.mkDerivation {
+      name = "dhall-compiled-package.nix";
+
+      buildCommand = ''
+        # Dhall requires that the cache is writable, even if it is never written to.
+        # We copy the cache from the input package to the current directory and
+        # set the cache as writable.
+        cp -r "${dhallPackage}/.cache" ./
+        export XDG_CACHE_HOME=$PWD/.cache
+        chmod -R +w ./.cache
+
+        dhall-to-nix <<< "${dhallPackage}/binary.dhall" > $out
+      '';
+
+      nativeBuildInputs = [ dhall-nix ];
+    };
+
+  in
+    import drv
diff --git a/nixpkgs/pkgs/build-support/dhall/to-nix.nix b/nixpkgs/pkgs/build-support/dhall/to-nix.nix
new file mode 100644
index 000000000000..96cc16e16f36
--- /dev/null
+++ b/nixpkgs/pkgs/build-support/dhall/to-nix.nix
@@ -0,0 +1,38 @@
+/* `dhallToNix` is a utility function to convert expressions in the Dhall
+    configuration language to their corresponding Nix expressions.
+
+    Example:
+      dhallToNix "{ foo = 1, bar = True }"
+      => { foo = 1; bar = true; }
+      dhallToNix "λ(x : Bool) → x == False"
+      => x : x == false
+      dhallToNix "λ(x : Bool) → x == False" false
+      => true
+
+    See https://hackage.haskell.org/package/dhall-nix/docs/Dhall-Nix.html for
+    a longer tutorial
+
+    Note that this uses "import from derivation", meaning that Nix will perform
+    a build during the evaluation phase if you use this `dhallToNix` utility
+*/
+{ stdenv, dhall-nix, writeText }:
+
+let
+  dhallToNix = code :
+    let
+      file = writeText "dhall-expression" code;
+
+      drv = stdenv.mkDerivation {
+        name = "dhall-compiled.nix";
+
+        buildCommand = ''
+          dhall-to-nix <<< "${file}" > $out
+        '';
+
+        buildInputs = [ dhall-nix ];
+      };
+
+    in
+      import drv;
+in
+  dhallToNix