Try #975:

ci.nix

@@ -24,14 +24,12 @@
     # Update supported-ghc-versions.md to reflect any changes made here.
     {
       ghc865 = true;
-    } // nixpkgs.lib.optionalAttrs (nixpkgsName == "R2003") {
+    } // nixpkgs.lib.optionalAttrs (nixpkgsName == "R2009") {
       ghc883 = false;
       ghc884 = true;
       ghc8101 = false;
       ghc8102 = true;
-      ghc810220201118 = false;
-    } // nixpkgs.lib.optionalAttrs (nixpkgsName == "R2009") {
-      ghc8102 = true;
+      ghc810220201118 = true;
     });
   systems = nixpkgs: nixpkgs.lib.filterAttrs (_: v: builtins.elem v supportedSystems) {
     # I wanted to take these from 'lib.systems.examples', but apparently there isn't one for linux!
@@ -42,7 +40,7 @@
     # We need to use the actual nixpkgs version we're working with here, since the values
     # of 'lib.systems.examples' are not understood between all versions
     let lib = nixpkgs.lib;
-    in lib.optionalAttrs (nixpkgsName == "R2003" && (__elem compiler-nix-name ["ghc865" "ghc884"])) {
+    in lib.optionalAttrs (nixpkgsName == "R2009" && (__elem compiler-nix-name ["ghc865" "ghc884"])) {
     inherit (lib.systems.examples) ghcjs;
   } // lib.optionalAttrs (system == "x86_64-linux" && (nixpkgsName == "R2009" || (!(__elem compiler-nix-name ["ghc8101" "ghc8102" "ghc810220201118"])))) {
     # Windows cross compilation is currently broken on macOS

nix/sources.json

@@ -79,16 +79,16 @@
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "nixpkgs": {
-        "branch": "nixpkgs-20.03-darwin",
+        "branch": "nixpkgs-20.09-darwin",
         "builtin": false,
         "description": "Nix Packages collection",
         "homepage": null,
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "7f73e46625f508a793700f5110b86f1a53341d6e",
-        "sha256": "1gijn6vm6hwy7sxdjd27qq0hjqpkq04npwbxybd9694x7h806823",
+        "rev": "f02bf8ffb9a5ec5e8f6f66f1e5544fd2aa1a0693",
+        "sha256": "156f48manydh8sbrs8j97mzvwdz2zaw51xlm0grrrnns5wa5aaln",
         "type": "tarball",
-        "url": "https://github.com/NixOS/nixpkgs/archive/7f73e46625f508a793700f5110b86f1a53341d6e.tar.gz",
+        "url": "https://github.com/NixOS/nixpkgs/archive/f02bf8ffb9a5ec5e8f6f66f1e5544fd2aa1a0693.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "nixpkgs-2003": {
@@ -106,6 +106,7 @@
     },
     "nixpkgs-2009": {
         "branch": "nixpkgs-20.09-darwin",
+        "builtin": false,
         "description": "Nix Packages collection",
         "homepage": null,
         "owner": "NixOS",

release.nix

@@ -1,7 +1,7 @@
 # 'supportedSystems' restricts the set of systems that we will evaluate for. Useful when you're evaluating
 # on a machine with e.g. no way to build the Darwin IFDs you need!
 { supportedSystems ? [ "x86_64-linux" "x86_64-darwin" ]
-, ifdLevel ? 3
+, ifdLevel ? 1
 , checkMaterialization ? false }:
 
 let
@@ -16,9 +16,9 @@ in allJobs // {
     required = genericPkgs.releaseTools.aggregate {
       name = "haskell.nix-required";
       meta.description = "All jobs required to pass CI";
-      # Hercules will require all of these, we just require the 20.03 jobs
+      # Hercules will require all of these, we just require the 20.09 jobs
       # to avoid stressing Hydra too much
-      constituents = lib.collect lib.isDerivation allJobs.R2003.ghc865.linux.native;
+      constituents = lib.collect lib.isDerivation allJobs.R2009.ghc865.linux.native;
     };
   }