src/default.nix: use a list of overlays rather than a single overlay

This commit changes from using a single overlay to using a
nixpkgs-like list of overlays chained together by
`lib.composeExtensions`.

src/default.nix

@@ -5,25 +5,31 @@ let
   nixpkgsArgs = { config.allowNonSource = false; };
   nixpkgsOnBuildForBuild  = pkgsFun nixpkgsArgs;
 
-  ownerboot = { hostPlatform?null, overlay }:
-    (lib.makeScope lib.callPackageWith (self: {
-      inherit lib nixpkgsOnBuildForBuild;
+  ownerboot = { hostPlatform?null, overlays }: let
+    base = final: prev: {
+      inherit hostPlatform;
+      nixpkgsOnBuildForHost = pkgsFun
+        (nixpkgsArgs
+         // (lib.optionalAttrs (final.hostPlatform!=null) {
+           crossSystem = final.hostPlatform;
+         }));
 
-      nixpkgsOnBuildForHost   = pkgsFun
-        (nixpkgsArgs // (lib.optionalAttrs (hostPlatform!=null) {
-          crossSystem = hostPlatform; }));
+      coreboot-toolchain = final.callPackage ./coreboot-toolchain { };
 
-      coreboot-toolchain = self.callPackage ./coreboot-toolchain { };
-
-      iasl_20180531 = self.nixpkgsOnBuildForBuild.callPackage ./coreboot/iasl_20180531 { };
-      coreboot      = self.callPackage ./coreboot {
-        initramfs_image = self.initramfs;
+      iasl_20180531 = final.nixpkgsOnBuildForBuild.callPackage ./coreboot/iasl_20180531 { };
+      coreboot      = final.callPackage ./coreboot {
+        initramfs_image = final.initramfs;
       };
-      kernel        = self.callPackage ./kernel { };
-      userspace     = self.callPackage ./userspace { };
-      initramfs     = self.callPackage ./initramfs { };
-    }))
-  .overrideScope' overlay;
+      kernel        = final.callPackage ./kernel { };
+      userspace     = final.callPackage ./userspace { };
+      initramfs     = final.callPackage ./initramfs { };
+    };
+  in
+    (lib.makeScope
+      lib.callPackageWith
+      (self: { inherit lib nixpkgsOnBuildForBuild; })).overrideScope'
+      (lib.foldl' lib.composeExtensions (_: prev: prev) ([base] ++ overlays));
+
 in {
   # one entry for each supported platform
   kevin = ownerboot (import ./platform/kevin { inherit lib; });

src/platform/am1i/default.nix

@@ -4,7 +4,7 @@
 {
   inherit hostPlatform;
 
-  overlay = (final: prev: {
+  overlays = [(final: prev: {
 
     platform_name = "am1i";
 
@@ -35,6 +35,6 @@
         cp src/mainboard/asus/am1i-a/cmos.layout $out/
       '';
     });
-  });
+  })];
 }
 

src/platform/kevin/default.nix

@@ -36,7 +36,7 @@ let
 in {
   inherit hostPlatform;
 
-  overlay = (final: prev: {
+  overlays = [(final: prev: {
     nixpkgsOnBuildForHost = prev.nixpkgsOnBuildForBuild.pkgsCross.aarch64-multiplatform;
 
     platform_name = "kevin";
@@ -107,5 +107,5 @@ in {
     };
 
     ectool = final.nixpkgsOnBuildForHost.callPackage (import ../../util/ectool { boardName = "kevin"; }) { };
-  });
+  })];
 }

src/platform/kgpe/default.nix

@@ -5,7 +5,7 @@
 {
   inherit hostPlatform;
 
-  overlay = (final: prev: {
+  overlays = [(final: prev: {
 
     platform_name = "kgpe";
 
@@ -70,5 +70,5 @@
         cp src/mainboard/asus/kgpe-d16/cmos.default $out/
     '';
     });
-  });
+  })];
 }