Fix Nixos Rust toolchain issues

Unfortunately Rust is a bit of a headache in Nixos. Previously this
project used the default nixpkgs rustc/cargo packages, but they're a few
versions out of date. This commit switches to using the installation via
Rustup with a pinned toolchain (https://nixos.wiki/wiki/Rust).

rust-toolchain.toml

@@ -0,0 +1,3 @@
+[toolchain]
+channel="1.75.0"
+components = ["rustfmt", "clippy", "rust-analyzer"]

shell.nix

@@ -1,20 +1,44 @@
 { pkgs ? import <nixpkgs> {} }:
 with pkgs;
-mkShell {
-  nativeBuildInputs = [
-    bintools-unwrapped
-    just
-    fastmod
-    glibc
-    cpulimit
-    rustc
-    cargo
-    gcc
-    rustfmt
-    clippy
-    linuxPackages_latest.perf
-    hyperfine
-  ];
+mkShell rec {
+    buildInputs = with pkgs; [
+      clang
+      # Replace llvmPackages with llvmPackages_X, where X is the latest LLVM version (at the time of writing, 16)
+      llvmPackages.bintools
+      # bintools-unwrapped
+      rustup
+      just
+      fastmod
+      glibc
+      cpulimit
+      gcc
+      clippy
+      linuxPackages_latest.perf
+      hyperfine
+    ];
 
-  RUST_SRC_PATH = "${pkgs.rust.packages.stable.rustPlatform.rustLibSrc}";
+    RUSTC_VERSION = pkgs.lib.readFile ./rust-toolchain.toml;
+    # https://github.com/rust-lang/rust-bindgen#environment-variables
+    LIBCLANG_PATH = pkgs.lib.makeLibraryPath [ pkgs.llvmPackages_latest.libclang.lib ];
+    shellHook = ''
+      export PATH=$PATH:''${CARGO_HOME:-~/.cargo}/bin
+      export PATH=$PATH:''${RUSTUP_HOME:-~/.rustup}/toolchains/$RUSTC_VERSION-x86_64-unknown-linux-gnu/bin/
+      '';
+    # Add precompiled library to rustc search path
+    RUSTFLAGS = (builtins.map (a: ''-L ${a}/lib'') [
+      # add libraries here (e.g. pkgs.libvmi)
+    ]);
+    # Add glibc, clang, glib and other headers to bindgen search path
+    BINDGEN_EXTRA_CLANG_ARGS =
+        # Includes with normal include path
+        (builtins.map (a: ''-I"${a}/include"'') [
+          # add dev libraries here (e.g. pkgs.libvmi.dev)
+          pkgs.glibc.dev
+        ])
+        # Includes with special directory paths
+        ++ [
+          ''-I"${pkgs.llvmPackages_latest.libclang.lib}/lib/clang/${pkgs.llvmPackages_latest.libclang.version}/include"''
+          ''-I"${pkgs.glib.dev}/include/glib-2.0"''
+          ''-I${pkgs.glib.out}/lib/glib-2.0/include/''
+        ];
 }