nimPackages.buildNimPackage: move to top-level

pkgs/development/nim-packages/build-nim-package/default.nix pkgs/development/compilers/nim/build-nim-package.nix

···
-{ lib, stdenv, nim, nim_builder }:
+{ lib, stdenv, nim1, nim2, nim_builder, defaultNimVersion ? 2 }:
 pkgArgs:
 
 let
···
       nim_builder --phase:install
       runHook postInstall
     '';
-    meta = { inherit (nim.meta) maintainers platforms; };
+    meta = { inherit (nim2.meta) maintainers platforms; };
   };
 
-  inputsOverride =
-    { depsBuildBuild ? [ ], nativeBuildInputs ? [ ], ... }: {
+  inputsOverride = { depsBuildBuild ? [ ], nativeBuildInputs ? [ ]
+    , requiredNimVersion ? defaultNimVersion, ... }:
+    (if requiredNimVersion == 1 then {
+      nativeBuildInputs = [ nim1 ] ++ nativeBuildInputs;
+    } else if requiredNimVersion == 2 then {
+      nativeBuildInputs = [ nim2 ] ++ nativeBuildInputs;
+    } else
+      throw "requiredNimVersion ${toString requiredNimVersion} is not valid")
+    // {
       depsBuildBuild = [ nim_builder ] ++ depsBuildBuild;
-      nativeBuildInputs = [ nim ] ++ nativeBuildInputs;
     };
 
   composition = finalAttrs:

pkgs/top-level/all-packages.nix

···
   nim = nim1;
   nimPackages = recurseIntoAttrs nim1.pkgs;
   nim2Packages = recurseIntoAttrs nim2.pkgs;
+  buildNimPackage = callPackage ../development/compilers/nim/build-nim-package.nix { };
 
   nrpl = callPackage ../development/tools/nrpl { };
 

pkgs/top-level/nim-packages.nix

···
-{ lib, pkgs, stdenv, newScope, nim, fetchFromGitHub }:
+{ lib, pkgs, stdenv, newScope, nim, buildNimPackage }:
 
 lib.makeScope newScope (self:
   let callPackage = self.callPackage;
   in {
     inherit nim;
-    buildNimPackage =
-      callPackage ../development/nim-packages/build-nim-package { };
+    buildNimPackage = buildNimPackage.override {
+      defaultNimVersion =
+        if lib.versionAtLeast nim.version "2.0.0" then 2 else 1;
+    };
 
     asciigraph = callPackage ../development/nim-packages/asciigraph { };