makeRustPlatform: refactor to make it easier to understand

It is now clearer what is supposed to be in the rust attribute set
without having studied type theory. The amount of code is identically.

pkgs/build-support/rust/default.nix

@@ -1,9 +1,5 @@
-{ stdenv, cacert, git, rust, cargo-vendor, python3 }:
-let
-  fetchcargo = import ./fetchcargo.nix {
-    inherit stdenv cacert git rust cargo-vendor python3;
-  };
-in
+{ stdenv, cacert, git, cargo, rustc, cargo-vendor, fetchcargo, python3 }:
+
 { name, cargoSha256 ? "unset"
 , src ? null
 , srcs ? null
@@ -45,7 +41,7 @@ in stdenv.mkDerivation (args // {
 
   patchRegistryDeps = ./patch-registry-deps;
 
-  buildInputs = [ cacert git rust.cargo rust.rustc ] ++ buildInputs;
+  buildInputs = [ cacert git cargo rustc ] ++ buildInputs;
 
   patches = cargoPatches ++ patches;
 

pkgs/build-support/rust/fetchcargo.nix

@@ -1,4 +1,4 @@
-{ stdenv, cacert, git, rust, cargo-vendor, python3 }:
+{ stdenv, cacert, git, cargo, cargo-vendor, python3 }:
 let cargo-vendor-normalise = stdenv.mkDerivation {
   name = "cargo-vendor-normalise";
   src = ./cargo-vendor-normalise.py;
@@ -20,7 +20,7 @@ in
 { name ? "cargo-deps", src, srcs, patches, sourceRoot, sha256, cargoUpdateHook ? "" }:
 stdenv.mkDerivation {
   name = "${name}-vendor";
-  nativeBuildInputs = [ cacert cargo-vendor git cargo-vendor-normalise rust.cargo ];
+  nativeBuildInputs = [ cacert cargo-vendor git cargo-vendor-normalise cargo ];
   inherit src srcs patches sourceRoot;
 
   phases = "unpackPhase patchPhase installPhase";

pkgs/build-support/rust/make-rust-platform.nix

@@ -0,0 +1,18 @@
+{ callPackage }:
+{ rustc, cargo, ... }: {
+  rust = {
+    inherit rustc cargo;
+  };
+
+  buildRustPackage = callPackage ./default.nix {
+    inherit rustc cargo;
+
+    fetchcargo = callPackage ./fetchcargo.nix {
+      inherit cargo;
+    };
+  };
+
+  rustcSrc = callPackage ../../development/compilers/rust/rust-src.nix {
+    inherit rustc;
+  };
+}

pkgs/top-level/all-packages.nix

@@ -7384,23 +7384,9 @@ with pkgs;
 
   defaultCrateOverrides = callPackage ../build-support/rust/default-crate-overrides.nix { };
 
+  makeRustPlatform = callPackage ../build-support/rust/make-rust-platform.nix {};
   rustPlatform = recurseIntoAttrs (makeRustPlatform rust);
 
-  makeRustPlatform = rust: lib.fix (self:
-    let
-      callPackage = newScope self;
-    in {
-      inherit rust;
-
-      buildRustPackage = callPackage ../build-support/rust {
-        inherit rust;
-      };
-
-      rustcSrc = callPackage ../development/compilers/rust/rust-src.nix {
-        inherit (rust) rustc;
-      };
-    });
-
   cargo-download = callPackage ../tools/package-management/cargo-download { };
   cargo-edit = callPackage ../tools/package-management/cargo-edit { };
   cargo-release = callPackage ../tools/package-management/cargo-release { };