Remove some flake specifics that can mess-up caching. (#1176)

* Remove flake specific sourceOverride that mess-up caching.

* Reduce evalPackages discrepency between flake/non-flake.

* Remove dependency on <nixpkgs> when importing sources.nix

default.nix

@@ -2,7 +2,7 @@
 , system ? builtins.currentSystem
 , sourcesOverride ? {}
 , ... }@args: rec {
-  sources  = (import ./nix/sources.nix) // sourcesOverride;
+  sources  = (import ./nix/sources.nix { inherit pkgs; }) // sourcesOverride;
   config   = import ./config.nix;
   overlays = [ allOverlays.combined ] ++ (
     if checkMaterialization == true
@@ -14,14 +14,7 @@
         }
       )]
       else []
-  ) ++ [(
-    final: prev: {
-        haskell-nix = prev.haskell-nix // {
-        inherit overlays;
-        sources = prev.haskell-nix.sources // sourcesOverride;
-      };
-    }
-  )];
+  );
   allOverlays = import ./overlays args;
   nixpkgsArgs = { inherit config overlays system; };
   pkgs = import sources.nixpkgs nixpkgsArgs;

flake.nix

@@ -14,21 +14,15 @@
 
     internal = rec {
       config = import ./config.nix;
-      # Use a shim for pkgs that does not depend on `builtins.currentSystem`.
-      sources = import ./nix/sources.nix {
-        pkgs = { fetchzip = builtins.fetchTarball; };
-      };
 
       nixpkgsArgs = {
         inherit config;
         overlays = [ self.overlay ];
       };
-
-      overlaysOverrideable = import ./overlays;
     };
 
     overlay = self.overlays.combined;
-    overlays = self.internal.overlaysOverrideable { sourcesOverride = self.internal.sources; };
+    overlays = import ./overlays {};
 
     legacyPackages = let
       genAttrs = lst: f:

nix/sources.json

@@ -92,7 +92,7 @@
     },
     "nixpkgs": {
         "branch": "nixpkgs-21.05-darwin",
-        "builtin": false,
+        "builtin": true,
         "description": "Nix Packages collection",
         "homepage": null,
         "owner": "NixOS",

overlays/default.nix

@@ -19,7 +19,7 @@ let
     nix-prefetch-git-minimal = import ./nix-prefetch-git-minimal.nix;
     gobject-introspection = import ./gobject-introspection.nix;
     hix = import ./hix.nix;
-    eval-packages = import ./eval-packages.nix;
+    eval-packages = import ./eval-packages.nix combined;
     ghcjs = import ./ghcjs.nix;
   };
 

overlays/eval-packages.nix

@@ -1,4 +1,4 @@
-final: prev: {
+haskellNixOverlay: final: prev: {
   # This overlay makes `evalPackages` is like `buildPackages`, but on
   # `builtins.currentSystem` (when not building a nix flake).
   # We do not pass the `config` or `overlays` (not in `final.haskell-nix.overlays`).
@@ -6,11 +6,9 @@ final: prev: {
   # derivations that use `evalPackages` (these should be eval time only derviations
   # used to build nix inputs for IFD, the generated nix should match and so derivations
   # that depend on the IFD should match).
-  evalPackages =
+  evalPackages = (import final.path {
     # If we are building a flake there will be no currentSystem attribute
-    if builtins ? currentSystem
-      then (import final.path {
-          inherit (final.haskell-nix) overlays;
-        }).buildPackages
-      else final.buildPackages;
-}
+    system = builtins.currentSystem or final.system;
+    overlays = [ haskellNixOverlay ];
+  }).buildPackages;
+}

overlays/haskell.nix

@@ -30,7 +30,7 @@ final: prev: {
             specJSON = stackageSourceJSON;
             override = "stackage";
           };
-        } // (import ../nix/sources.nix) // sourcesOverride;
+        } // (import ../nix/sources.nix { pkgs = final; }) // sourcesOverride;
 
         # We provide a `callPackage` function to consumers for
         # convenience.  We will however refrain from using it
@@ -706,7 +706,7 @@ final: prev: {
               , crossPlatforms ? p: []
               }:
               let packageNames = project: builtins.attrNames (packages project.hsPkgs);
-                  packagesForProject = prefix: project: 
+                  packagesForProject = prefix: project:
                     final.lib.concatMap (packageName:
                       let package = project.hsPkgs.${packageName};
                       in final.lib.optional (package.components ? library)
@@ -721,7 +721,7 @@ final: prev: {
                             { name = "${prefix}${packageName}:test:${n}"; value = v; })
                           (package.components.tests)
                     ) (packageNames project);
-                  checksForProject = prefix: project: 
+                  checksForProject = prefix: project:
                     final.lib.concatMap (packageName:
                       let package = project.hsPkgs.${packageName};
                       in final.lib.mapAttrsToList (n: v: