don’t nest jobsets

hydra/jobsets.nix

@@ -7,8 +7,10 @@
   systems = ["x86_64-linux" "aarch64-linux" "riscv64-linux"];
   nixpkgs_version = ["master" "nixos-22.05"];
   mkJobsets = system: version:
-    (pkgs.lib.mapAttrs (
+    (pkgs.lib.mapAttrs' (
         num: info: {
+          name = "${system}-${version}-pr${num}";
+          value = {
             enabled = 1;
             hidden = false;
             description = "PR ${num} (${system}-${version}): ${info.title}";
@@ -35,11 +37,12 @@
                 value = system;
               };
             };
+          };
         }
       )
       prs)
     // {
-      main = {
+      "${system}-${version}" = {
         enabled = 1;
         hidden = false;
         description = "nix-packages ${system}-${version}";
@@ -69,17 +72,7 @@
       };
     };
 
-  mapToAttrs = f: list: pkgs.lib.listToAttrs (map f list);
+  concatAttrs = pkgs.lib.foldr (a: b: a // b) {};
 
-  jobsets =
-    mapToAttrs (system: {
-      name = system;
-      value =
-        mapToAttrs (version: {
-          name = version;
-          value = mkJobsets system version;
-        })
-        nixpkgs_version;
-    })
-    systems;
+  jobsets = concatAttrs (pkgs.lib.concatMap (system: map (version: mkJobsets system version) nixpkgs_version) systems);
 in {jobsets = pkgs.writeText "jobsets.json" (builtins.toJSON jobsets);}