nix/rust-platform: remove rustcSrc which had to be kept in sync

default.nix

@@ -15,7 +15,7 @@ let
 
       nativeBuildInputs = [ cargo-xbuild ];
       buildPhase = ''
-        export XARGO_RUST_SRC="${rustPlatform.rust.rustc.src}/library"
+        export XARGO_RUST_SRC="${rustPlatform.rust.rustc}/lib/rustlib/src/rust/library"
         export CARGO_HOME=$(mktemp -d cargo-home.XXX)
         pushd ${crate}
         cargo xbuild --release --frozen \

nix/rust-platform.nix

@@ -1,24 +1,20 @@
 { pkgs }:
 
 let
-  rustcSrc = pkgs.fetchgit {
-    url = "https://github.com/rust-lang/rust.git";
-    # sync with git_commit_hash from pkg.rust in channel-rust-nightly.toml
-    rev = "8dae8cdcc8fa879cea6a4bbbfa5b32e97be4c306";
-    sha256 = "1c9wdwqvskchiqkxqnl516z2yajs2nbs31y4j6m2jz945dj8x4xc";
-    fetchSubmodules = true;
-  };
   rustManifest = ./channel-rust-nightly.toml;
 
   targets = [];
   rustChannelOfTargets = _channel: _date: targets:
     (pkgs.lib.rustLib.fromManifestFile rustManifest {
       inherit (pkgs) stdenv fetchurl patchelf;
-    }).rust.override { inherit targets; };
+    }).rust.override {
+      inherit targets;
+      extensions = ["rust-src"];
+    };
   rust =
     rustChannelOfTargets "nightly" null targets;
 in
   pkgs.recurseIntoAttrs (pkgs.makeRustPlatform {
-    rustc = rust // { src = rustcSrc; };
+    rustc = rust;
     cargo = rust;
   })

shell.nix

@@ -17,7 +17,7 @@ in
       (import ./nix/mkbootimage.nix { inherit pkgs; })
     ];
 
-    XARGO_RUST_SRC = "${rustPlatform.rust.rustc.src}/library";
+    XARGO_RUST_SRC = "${rustPlatform.rust.rustc}/lib/rustlib/src/rust/library";
 
     shellHook = ''
       echo "Run 'cargo xbuild --release -p ...' to build."