This PR adds support for evaluating flakes directly using nix eval to make pure evaluation work with Nix 2.21+. Fixes #202.

Been procrastinating on this for a long time, but with NixOS 24.11 releasing soon carrying Nix 2.24 as the default, it's finally time to do it.

This is based on the existing experimental support for the colmenaHive output. Instead of using the eval.nix bundled with the Colmena executable against the "raw" colmena output, the colmenaHive output contains the "prepared" hive.

Usage

Your flake needs to depend on Colmena as an input and expose a new colmenaHive output containing the result of colmena.lib.makeHive:

 {
   inputs = {
+    # ADDED: Colmena input
+    colmena.url = "github:zhaofengli/colmena";

     # ... Rest of configuration ...
   };
   outputs = { self, colmena, ... }: {
+    # ADDED: New colmenaHive output
+    colmenaHive = colmena.lib.makeHive self.outputs.colmena;

     # Your existing colmena output
     colmena = {
       # ... Rest of configuration ...
     };
   };
 }

Then, add --experimental-flake-eval to colmena invocations.

Current Limitations

The following isn't supported with --experimental-flake-eval:

• colmena eval --instantiate
• --evaluator streaming