Add source scanning

default.nix

@@ -8,8 +8,58 @@ let
     { modules ? [] }: lib.evalModules {
       check = true;
       modules = builtinModules ++ modules;
+      specialArgs = { inherit scanProjectModules; };
     };
 
+  scanProjectModules = scan "nix/project-module.nix";
+
+  # Like a PATH search, where filePath is like bin/somecommand
+  #
+  #     scan : string -> sources -> listOf module
+  #
+  # Arguments
+  #
+  #     filePath : string       File to look for in the sources
+  #
+  #     sources : attrsOf path  Sources that may contain a file named ${filePath}
+  #            or path          or a path that has such a Nix expression
+  scan = filePath:
+    let
+      withAsserts =
+        assert builtins.typeOf filePath == "string";
+        x: x;
+
+      importify =
+        f: x:
+          if lib.types.path.check x
+          then builtins.addErrorContext
+            "while scanning for modules in ${toString x}"
+            (f (import x))
+          else builtins.addErrorContext
+            "while scanning for modules"
+            (f x);
+
+      scanAttrs = attrs:
+        lib.concatLists (
+          lib.mapAttrsToList (
+            key: value:
+              builtins.addErrorContext
+                "while scanning attribute ${key}"
+                (scanIfDirlike value)
+          )
+            attrs
+        );
+
+      scanIfDirlike = value:
+        if lib.types.path.check value
+        then let
+          potential = value + "/${filePath}";
+        in
+          if builtins.pathExists potential then [ potential ] else []
+        else [];
+    in
+      withAsserts (importify scanAttrs);
+
   builtinModules = [
     ./modules/root.nix
     ./modules/nixpkgs.nix

nix/project.nix

@@ -1,9 +1,6 @@
+{ scanProjectModules, ... }:
 {
-  # imports = scan "nix/project-module.nix" ./sources.nix;
-
-  imports = [
-    ((import ./sources.nix).nix-pre-commit-hooks + "/nix/project-module.nix")
-  ];
+  imports = scanProjectModules ./sources.nix;
 
   root = ../.;
   pinning.niv.enable = true;