build(flake): Replace self-packaged cranelift with rustup's

Motivation
==========
The self-packed one sort-of worked, but was rather flaky, while the one
from rustup obviously works, as it's an officially distributed part.

Running it
==========
Instead of the `cargo clif [build, etc.]` you now need to run (on nightly):
```
RUSTFLAGS="-Zcodegen-backend=cranelift" cargo build
```

Performance
===========
On my system I noticed, that a debug build takes around 20 sec *more*
with cranelift, compared to the default LLVM backend.

One possible hypothesis, for that could be, that cranelift does
not link via `mold` but instead still uses GNU's `gold`.

On the other hand, the performance decrease could also be caused
by the fact, that it's an early preview and some optimizations are
still lacking.

flake.lock

@@ -76,9 +76,7 @@
         "flake-compat": "flake-compat",
         "flake-utils": "flake-utils",
         "nixpkgs": "nixpkgs",
-        "rust-overlay": "rust-overlay",
+        "rust-overlay": "rust-overlay"
-        "rustc_cranelift_backend": "rustc_cranelift_backend",
-        "rustc_cranelift_backend_src": "rustc_cranelift_backend_src"
       }
     },
     "rust-overlay": {
@@ -104,36 +102,6 @@
         "type": "github"
       }
     },
-    "rustc_cranelift_backend": {
-      "flake": false,
-      "locked": {
-        "lastModified": 1698679294,
-        "narHash": "sha256-plG6ifmuMwy7pr0KE19Oz+HKLH+4UDuuXZ1u0s9RtNQ=",
-        "owner": "bjorn3",
-        "repo": "rustc_codegen_cranelift",
-        "rev": "9a33f82140c6da6e5808253309c674554b93e9fe",
-        "type": "github"
-      },
-      "original": {
-        "owner": "bjorn3",
-        "ref": "dev",
-        "repo": "rustc_codegen_cranelift",
-        "type": "github"
-      }
-    },
-    "rustc_cranelift_backend_src": {
-      "flake": false,
-      "locked": {
-        "lastModified": 1698679361,
-        "narHash": "sha256-vc7T92wEfufuPc8q2/xq4mQK/uFfoG7pKOVWYxbHzds=",
-        "type": "tarball",
-        "url": "https://github.com/bjorn3/rustc_codegen_cranelift/releases/download/dev/cg_clif-x86_64-unknown-linux-gnu.tar.xz"
-      },
-      "original": {
-        "type": "tarball",
-        "url": "https://github.com/bjorn3/rustc_codegen_cranelift/releases/download/dev/cg_clif-x86_64-unknown-linux-gnu.tar.xz"
-      }
-    },
     "systems": {
       "locked": {
         "lastModified": 1681028828,

flake.nix

@@ -29,16 +29,6 @@
         flake-utils.follows = "flake-utils";
       };
     };
-
-    # cranelift
-    rustc_cranelift_backend = {
-      url = "github:bjorn3/rustc_codegen_cranelift/dev";
-      flake = false;
-    };
-    rustc_cranelift_backend_src = {
-      url = "https://github.com/bjorn3/rustc_codegen_cranelift/releases/download/dev/cg_clif-x86_64-unknown-linux-gnu.tar.xz";
-      flake = false;
-    };
   };
 
   outputs = {
@@ -47,8 +37,6 @@
     crane,
     flake-utils,
     rust-overlay,
-    rustc_cranelift_backend,
-    rustc_cranelift_backend_src,
     ...
   }:
     flake-utils.lib.eachDefaultSystem (system: let
@@ -74,94 +62,20 @@
           done
         '';
       };
-      c_rust = pkgs.rust-bin.fromRustupToolchainFile "${rustc_cranelift_backend}/rust-toolchain";
-      rcb = pkgs.stdenv.mkDerivation {
-        pname = "rustc_cranelift_backend";
-        version = "1.0";
-        buildInputs = [c_rust];
-        nativeBuildInputs = with pkgs; [gawk fd];
-        srcs = ["${rustc_cranelift_backend_src}" "${c_rust}"];
-        sourceRoot = ".";
-        postUnpack = ''
-          rust_dir="$(fd . --max-depth 1 | awk '!/source/ && !/env-vars/')"
-
-          # remove unneeded stuff
-          rm -r "$rust_dir"/{bin,nix-support,share};
-          rm -r "$rust_dir"/lib/rustlib/{etc,src,rustc-src};
-
-          cp -r "$rust_dir"/. source/extra_dependencies
-          rm -r "$rust_dir"
-          cd source
-        '';
-        postPatch = ''
-          # patch bins
-          for file in $(fd . --type file);do
-              file="$(file --mime "$file" | awk 'BEGIN{FS=":"}/application\/x-pie-executable/{print $1}')";
-              if [ "$file" ]; then
-                  echo "file: '$file' matches";
-                  correct_interpreter_path="$(ldd "$file" | tail -n1 | awk 'BEGIN{FS="=> "} {print $2}' | awk 'BEGIN{FS=" "}{print $1}')"
-                  echo "correct interpreter path is: '$correct_interpreter_path'"
-                  patchelf --set-interpreter "$correct_interpreter_path" "$file"
-
-                  if [ "$(patchelf --print-interpreter "$file")" = "$correct_interpreter_path" ];then
-                    echo "Set interpreter";
-                  else
-                    echo "Failed to set interprter, the interpreter still is $(patchelf --print-interpreter )";
-                    exit 1
-                  fi
-              fi
-          done
-
-          # patch libs
-          all_files=$(mktemp);
-          for file in $(fd .);do
-              canonical_path="$(readlink -f "$file")"
-              file="$(file --mime "$canonical_path" | awk 'BEGIN{FS=":"}/application\/x-sharedlib/{print $1}')";
-              if [ "$file" ]; then
-                  echo "$file" >> $all_files;
-              fi
-          done
-          while read -r file; do
-              echo "___________________";
-              echo "Checking file: '$file'";
-              is_missing="$(ldd "$file" | awk 'BEGIN{FS="=>"}{if (/not found/){print $1}}')"
-              if [ "$is_missing" ];then
-                  echo "Warning: The following things are missing:";
-                  for line in $is_missing; do
-                      echo "  $line";
-                  done
-                  echo
-                  for line in $is_missing; do
-                      echo "Searching for a substitute for '$line'"
-                      substitute="$(grep "$line" "$all_files" | awk 'BEGIN{FS=" "}{print $1}' | tail -n1)";
-                      if [ "$substitute" ]; then
-                          echo "Found '$substitute', which can substitute '$line'"
-                          echo "Patching.."
-                          patchelf --replace-needed "$line" "$(readlink -f "$substitute")" "$file";
-                      else
-                          echo "Error: Failed to find a substitute"
-                      fi
-                  done
-              else
-                  echo "This file is not missing anything"
-              fi
-          done < $all_files
-          rm $all_files
-        '';
-        installPhase = ''
-          install -d $out/
-          cp -r ./. $out/
-        '';
-      };
       pkgs = import nixpkgs {
         inherit system;
         overlays = [(import rust-overlay)];
       };
 
-      nightly = false;
+      nightly = true;
       rust =
         if nightly
-        then pkgs.rust-bin.selectLatestNightlyWith (toolchain: toolchain.default)
+        then
+          (pkgs.rust-bin.selectLatestNightlyWith (toolchain:
+              toolchain.default))
+          .override {
+            extensions = ["rustc-codegen-cranelift-preview"];
+          }
         else pkgs.rust-bin.stable.latest.default;
 
       craneLib = (crane.mkLib pkgs).overrideToolchain rust;
@@ -169,7 +83,6 @@
       nativeBuildInputs = with pkgs; [
         pkg-config
         mold'
-        rcb
       ];
       buildInputs = with pkgs; [
         openssl