dhallDirectoryToNix: add this utility functionorigin/dhallDirectoryToNix

2 files changed, 27 insertions, 0 deletions

diff --git a/pkgs/build-support/dhall/directory-to-nix.nix b/pkgs/build-support/dhall/directory-to-nix.nix
new file mode 100644
index 000000000000..d751e19df3fc
--- /dev/null
+++ b/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/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index 9f0b07924166..746e78602460 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -293,6 +293,8 @@ with pkgs;
 
   crow-translate = libsForQt5.callPackage ../applications/misc/crow-translate { };
 
+  dhallDirectoryToNix = callPackage ../build-support/dhall/directory-to-nix.nix { };
+
   dhallPackageToNix = callPackage ../build-support/dhall/package-to-nix.nix { };
 
   dhallToNix = callPackage ../build-support/dhall/to-nix.nix { };