Allow to specify some flake outputs from Nickel

Add `flake` field to `project.ncl` that allows to specify certain flake outputs. For example, you can add lines like these to run `hello` as an app or a check: flake.apps.hello.program = nix-s%"%{import_nix "nixpkgs#hello"}/bin/hello"%, flake.checks.hello = import_nix "nixpkgs#hello", I will be gragually migrating apps and checks from our `flake.nix` to `project.ncl` using this. Part of #58
nickel-lang · Sep 25, 2023 · 8deb2fb · 8deb2fb
1 parent 8c67177
commit 8deb2fb
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Showing 2 changed files with 24 additions and 13 deletions.
diff --git a/flake.nix b/flake.nix
@@ -35,21 +35,24 @@
       flake-utils.lib.eachSystem systems (system: let
         lib = self.lib.${system};
         pkgs = nixpkgs.legacyPackages.${system};
+        nickelOutputs = lib.importNcl {
+          inherit baseDir flakeInputs lockFileContents;
+        };
       in
-        {
-          apps.regenerate-lockfile = lib.regenerateLockFileApp lockFileContents;
-        }
-        // pkgs.lib.optionalAttrs (builtins.readDir baseDir ? "project.ncl") rec {
-          nickelOutputs = lib.importNcl {
-            inherit baseDir flakeInputs lockFileContents;
-          };
-          packages =
-            if nickelOutputs ? packages && nickelOutputs.packages ? default
-            then {
-              default = nickelOutputs.packages.default;
+        # Can't do just `{inherit nickelOutputs;} // nickelOutputs.flake` because of infinite recursion over self
+        pkgs.lib.optionalAttrs (builtins.readDir baseDir ? "project.ncl") {
+          inherit nickelOutputs;
+          packages = nickelOutputs.packages or {} // nickelOutputs.flake.packages or {};
+          checks = nickelOutputs.flake.checks or {};
+          # Can't define this app in Nickel, yet
+          apps =
+            {
+              regenerate-lockfile = lib.regenerateLockFileApp lockFileContents;
             }
-            else {};
-          devShells = nickelOutputs.shells or {};
+            // nickelOutputs.flake.apps or {};
+          # We can't just copy `shells` to `flake.devShells` in the contract
+          # because of a bug in Nickel: TBD, see https://matrix.to/#/!LYbBGmwIxxrVNjIdah:matrix.org/$qInwUWPPw9O7DkO6hGItRQOyhhP_nkSmtcUcVVIIpnE
+          devShells = nickelOutputs.shells or {} // nickelOutputs.flake.devShells or {};
         });
 
     computedOutputs = outputsFromNickel ./. inputs {

diff --git a/lib/contracts.ncl b/lib/contracts.ncl
@@ -309,6 +309,13 @@ from the Nix world) or a derivation defined in Nickel.
     "default" | NickelDerivation = dev,
   },
 
+  FlakeOutputs = {
+    packages | { _ | Derivation } | optional,
+    checks | { _ | Derivation } | optional,
+    devShells | { _ | Derivation } | optional,
+    apps | { _ | { type = "app", program | NixString } } | optional,
+  },
+
   # TODO: have the actual contract for the result of an expression. It's pretty
   # open (could be an integer, a derivation, a record of derivations, etc.) but
   # it still obeys some rules: if the `type` field is set to a known predefined
@@ -320,6 +327,7 @@ from the Nix world) or a derivation defined in Nickel.
     shells
       | OrganistShells
       | optional,
+    flake | FlakeOutputs | optional,
     ..
   },
 }