top-level: Make `overridePackages` extend rather than replace existing overrides

1 files changed, 60 insertions, 51 deletions

diff --git a/pkgs/top-level/default.nix b/pkgs/top-level/default.nix
index 2eb7fb34b4d..d0dc231650c 100644
--- a/pkgs/top-level/default.nix
+++ b/pkgs/top-level/default.nix
@@ -61,6 +61,35 @@ let
     inherit system bootStdenv noSysDirs config crossSystem platform lib;
   };
 
+  stdenvAdapters = self: super:
+    let res = import ../stdenv/adapters.nix self; in res // {
+      stdenvAdapters = res;
+    };
+
+  trivialBuilders = self: super:
+    (import ../build-support/trivial-builders.nix {
+      inherit lib; inherit (self) stdenv stdenvNoCC; inherit (self.xorg) lndir;
+    });
+
+  stdenvDefault = self: super: (import ./stdenv.nix topLevelArguments) {} pkgs;
+
+  allPackages = self: super:
+    let res = import ./all-packages.nix topLevelArguments res self;
+    in res;
+
+  aliases = self: super: import ./aliases.nix super;
+
+  # stdenvOverrides is used to avoid circular dependencies for building
+  # the standard build environment. This mechanism uses the override
+  # mechanism to implement some staged compilation of the stdenv.
+  #
+  # We don't want stdenv overrides in the case of cross-building, or
+  # otherwise the basic overridden packages will not be built with the
+  # crossStdenv adapter.
+  stdenvOverrides = self: super:
+    lib.optionalAttrs (crossSystem == null && super.stdenv ? overrides)
+      (super.stdenv.overrides super);
+
   # Allow packages to be overridden globally via the `packageOverrides'
   # configuration option, which must be a function that takes `pkgs'
   # as an argument and returns a set of new or overridden packages.
@@ -68,54 +97,34 @@ let
   # (un-overridden) set of packages, allowing packageOverrides
   # attributes to refer to the original attributes (e.g. "foo =
   # ... pkgs.foo ...").
-  pkgs = pkgsWithOverrides (self: config.packageOverrides or (super: {}));
-
-  # Return the complete set of packages, after applying the overrides
-  # returned by the `overrider' function (see above).  Warning: this
-  # function is very expensive!
-  pkgsWithOverrides = overrider:
-    let
-      stdenvAdapters = self: super:
-        let res = import ../stdenv/adapters.nix self; in res // {
-          stdenvAdapters = res;
-        };
-
-      trivialBuilders = self: super:
-        (import ../build-support/trivial-builders.nix {
-          inherit lib; inherit (self) stdenv stdenvNoCC; inherit (self.xorg) lndir;
-        });
-
-      stdenvDefault = self: super: (import ./stdenv.nix topLevelArguments) {} pkgs;
-
-      allPackagesArgs = topLevelArguments // { inherit pkgsWithOverrides; };
-      allPackages = self: super:
-        let res = import ./all-packages.nix allPackagesArgs res self;
-        in res;
-
-      aliases = self: super: import ./aliases.nix super;
-
-      # stdenvOverrides is used to avoid circular dependencies for building
-      # the standard build environment. This mechanism uses the override
-      # mechanism to implement some staged compilation of the stdenv.
-      #
-      # We don't want stdenv overrides in the case of cross-building, or
-      # otherwise the basic overridden packages will not be built with the
-      # crossStdenv adapter.
-      stdenvOverrides = self: super:
-        lib.optionalAttrs (crossSystem == null && super.stdenv ? overrides)
-          (super.stdenv.overrides super);
-
-      customOverrides = self: super:
-        lib.optionalAttrs (bootStdenv == null) (overrider self super);
-    in
-      lib.fix' (
-        lib.extends customOverrides (
-          lib.extends stdenvOverrides (
-            lib.extends aliases (
-              lib.extends allPackages (
-                lib.extends stdenvDefault (
-                  lib.extends trivialBuilders (
-                    lib.extends stdenvAdapters (
-                      self: {}))))))));
-in
-  pkgs
+  configOverrides = self: super:
+    lib.optionalAttrs (bootStdenv == null)
+      ((config.packageOverrides or (super: {})) super);
+
+  # The complete chain of package set builders, applied from bottom to top
+  toFix = lib.fold lib.extends (self: {}) [
+    configOverrides
+    stdenvOverrides
+    aliases
+    allPackages
+    stdenvDefault
+    trivialBuilders
+    stdenvAdapters
+  ];
+
+  # Use `overridePackages` to easily override this package set.
+  # Warning: this function is very expensive and must not be used
+  # from within the nixpkgs repository.
+  #
+  # Example:
+  #  pkgs.overridePackages (self: super: {
+  #    foo = super.foo.override { ... };
+  #  }
+  #
+  # The result is `pkgs' where all the derivations depending on `foo'
+  # will use the new version.
+
+  # Return the complete set of packages. Warning: this function is very
+  # expensive!
+  pkgs = lib.makeExtensibleWithCustomName "overridePackages" toFix;
+in pkgs