nixpkgs-bootstrap: hoist config to callArgs level, to simplify the call site

impure.nix

@@ -8,11 +8,10 @@
   localSystem ? builtins.currentSystem,
 }:
 let
-  mkNixpkgs = import ./pkgs/by-name/nixpkgs-bootstrap/mkNixpkgs.nix {};
-  mkPkgs = branch: config: (
-    import ./pkgs/by-name/nixpkgs-bootstrap/${branch}.nix {
-      mkNixpkgs = args: mkNixpkgs (config // args);
-    }
+  mkPkgs = branch: config: let
+    mkNixpkgs = import ./pkgs/by-name/nixpkgs-bootstrap/mkNixpkgs.nix config;
+  in (
+    import ./pkgs/by-name/nixpkgs-bootstrap/${branch}.nix { inherit mkNixpkgs; }
   ).pkgs.extend (import ./overlays/all.nix);
   pkgs = mkPkgs "master" { inherit localSystem; };
   inherit (pkgs) lib;

pkgs/by-name/nixpkgs-bootstrap/mkNixpkgs.nix

@@ -42,6 +42,9 @@
   fetchzip ? null,
   stdenv ? null,
   unstableGitUpdater ? null,
+#VVV config
+  localSystem ? if stdenv != null then stdenv.buildPlatform.system else builtins.currentSystem,  #< not available in pure mode
+  system ? if stdenv != null then stdenv.hostPlatform.system else localSystem,
 }:
 let
   # nixpkgs' update-source-version (updateScript) calculates the new hash for a `src` by specifying this hardcoded bogus hash and then attempting to realize it.
@@ -62,9 +65,6 @@ let
     rev ? "",
     sha256 ? "",
     version ? "",
-  #VVV config
-    localSystem ? if stdenv != null then stdenv.buildPlatform.system else builtins.currentSystem,  #< not available in pure mode
-    system ? if stdenv != null then stdenv.hostPlatform.system else localSystem,
   }@args: let
     url = "https://github.com/NixOS/nixpkgs/archive/${rev}.tar.gz";
     pname = "nixpkgs-${branch}";
@@ -126,47 +126,38 @@ let
     } else {});
     nixpkgs = import patchedSrc nixpkgsArgs;
   in
-    if rev == "" && sha256 == "" && version == "" then
-      # allow `impure.nix` to invoke this with only `branch`, and we figure out the details for it.
-      # TODO: remove this code path.
-      import ./${branch}.nix {
-        mkNixpkgs = args': mkNixpkgs ({
-          inherit localSystem system;
-        } // args');
-      }
-    else
-      patchedSrc.overrideAttrs (base: {
-        # attributes needed for update scripts.
-        # TODO: should be possible to pass these straight through `applyPatches` instead of using `overrideAttrs`.
-        inherit version;
-        pname = "nixpkgs";
-        passthru = (base.passthru or {}) // {
-          pkgs = nixpkgs;
+    patchedSrc.overrideAttrs (base: {
+      # attributes needed for update scripts.
+      # TODO: should be possible to pass these straight through `applyPatches` instead of using `overrideAttrs`.
+      inherit version;
+      pname = "nixpkgs";
+      passthru = (base.passthru or {}) // {
+        pkgs = nixpkgs;
 
-          src = {
-            # required by unstableGitUpdater
-            gitRepoUrl = "https://github.com/NixOS/nixpkgs.git";
-            inherit rev;
-          } // src';
+        src = {
+          # required by unstableGitUpdater
+          gitRepoUrl = "https://github.com/NixOS/nixpkgs.git";
+          inherit rev;
+        } // src';
 
-          # required so that unstableGitUpdater can know in which file the `rev` variable can be updated in.
-          meta.position = let
-            position = builtins.unsafeGetAttrPos "rev" args;
-          in
-            "${position.file}:${toString position.line}";
+        # required so that unstableGitUpdater can know in which file the `rev` variable can be updated in.
+        meta.position = let
+          position = builtins.unsafeGetAttrPos "rev" args;
+        in
+          "${position.file}:${toString position.line}";
 
-          # while we could *technically* use `nixpkgs.<...>` updateScript
-          # that can force maaany rebuilds on staging/staging-next.
-          # updateScript = nix-update-script {
-          #   extraArgs = [ "--version=branch=${branch}" ];
-          # };
-          updateScript = unstableGitUpdater {
-            # else the update script tries to walk 10000's of commits to find a tag
-            hardcodeZeroVersion = true;
-            inherit branch;
-          };
+        # while we could *technically* use `nixpkgs.<...>` updateScript
+        # that can force maaany rebuilds on staging/staging-next.
+        # updateScript = nix-update-script {
+        #   extraArgs = [ "--version=branch=${branch}" ];
+        # };
+        updateScript = unstableGitUpdater {
+          # else the update script tries to walk 10000's of commits to find a tag
+          hardcodeZeroVersion = true;
+          inherit branch;
         };
-      })
+      };
+    })
   ;
 in
   mkNixpkgs