Fix nix build for c2rust.

This commit adds a number of improvements to the nix build for c2rust
the main highlights are:

- A c2rust package is provided, allowing nix users to install and run
  c2rust itself, instead of just getting a development environment
  from nix.
- Update LLVM / clang to version 18.
- Test cases pass in the c2rust dev environment now.

Some fixes include...

- Removing oxalica and just using fenix. Mixing rust overlays in nix
  was causing issues.
- Use the nix tinycbor package to build c2rust. The c2rust cmake files
  add an external dependency on tinycbor, which causes sandboxed nix
  builds to fail because they cannot fetch the package. This involves
  patching the CMakeLists.txt file, and using pkg-config to find the
  system tinycbor library. Note: in the dev shell cmake will still
  fetch the external tinycbor.
- Use the C2RUST_TINYCBOR_PATH environment variable, if it exists, to
  find tinycbor in c2rust-ast-exporter's build.rs
- Use bindgenHook to make sure Rust's bindgen can find header files.
- Update the test_translator.py script to include nix flags in compiler_commands.json
  Messing with bindgenHook, disable checks so package builds.
- test_translator.py will use nix dependencies when the environment
  variable C2RUST_USE_NIX=1
  + Passing the --use-nix flag to test_translator.py will also
      explicitly force the script to use nix dependencies.

Author: Chobbes

c2rust-ast-exporter/build.rs

@@ -149,8 +149,18 @@ fn build_native(llvm_info: &LLVMInfo) {
         }
     };
 
-    // Statically link against 'clangAstExporter' which requires 'tinycbor'
+    // Use a custom tinybor directory via an environment variable
+    if let Ok(tinycbor_dir) = env::var("TINYCBOR_DIR") {
+        let include_dir = Path::new(&tinycbor_dir).join("include");
+        let lib_dir = Path::new(&tinycbor_dir).join("lib");
+
+        println!("cargo:rustc-link-search=native={}", lib_dir.display());
+        println!("cargo:rerun-if-changed={}", include_dir.display());
+    }
+
     println!("cargo:rustc-link-lib=static=tinycbor");
+
+    // Statically link against 'clangAstExporter' which requires 'tinycbor'
     println!("cargo:rustc-link-lib=static=clangAstExporter");
 
     println!("cargo:rustc-link-search=native={}", llvm_lib_dir);

flake.lock

@@ -2,54 +2,69 @@
   description = "Flake for c2rust";
 
   inputs = {
-    nixpkgs.url = "github:NixOS/nixpkgs/nixos-23.11";
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
     utils.url = "github:numtide/flake-utils";
     fenix = {
       url = "github:nix-community/fenix";
-    };
-    oxalica = {
-      url = "github:oxalica/rust-overlay";
+      inputs.nixpkgs.follows = "nixpkgs";
     };
   };
 
-  outputs = inputs@{ self, nixpkgs, utils, fenix, oxalica}:
+  outputs = inputs@{ self, nixpkgs, utils, fenix}:
     utils.lib.eachDefaultSystem (system:
-    let
-        fenixStable = fenix.packages.${system}.fromToolchainFile {
-          file = ./rust-toolchain.toml;
-          sha256 = "sha256-r/8YBFuFa4hpwgE3FnME7nQA2Uc1uqj0eCE1NWmI1u0";
-        };
+      let
+        fenixToolchain =
+          let
+            toml = with builtins; (fromTOML (readFile ./rust-toolchain.toml)).toolchain;
+          in
+            (fenix.packages.${system}.fromToolchainName {
+              name = toml.channel;
+              sha256 = "sha256-r/8YBFuFa4hpwgE3FnME7nQA2Uc1uqj0eCE1NWmI1u0";
+            })."completeToolchain";
+
         pkgs = import nixpkgs {
           inherit system;
-          overlays = [
-            (import oxalica)
-          ];
+          overlays = [ ];
           config = {
             allowUnfree = true;
           };
         };
-        in {
-          defaultPackage = self.devShell.${system};
-          devShell = pkgs.mkShell.override { } {
 
-            LIBCLANG_PATH = "${pkgs.llvmPackages_14.libclang.lib}/lib";
-            CMAKE_LLVM_DIR = "${pkgs.llvmPackages_14.libllvm.dev}/lib/cmake/llvm";
-            CMAKE_CLANG_DIR = "${pkgs.llvmPackages_14.libclang.dev}/lib/cmake/clang";
-            shellHook = ''
-              export CARGO_TARGET_DIR="$(git rev-parse --show-toplevel)/target_dirs/nix_rustc";
-            '';
-            RUST_SRC_PATH = pkgs.rustPlatform.rustLibSrc;
-            buildInputs =
+        myLLVM = pkgs.llvmPackages_18;
+        myStdenv = pkgs.clang18Stdenv;
+
+        rustPlatform = pkgs.makeRustPlatform {
+          cargo = fenixToolchain;
+          rustc = fenixToolchain;
+        };
+        env = with pkgs; {
+          LIBCLANG_PATH = "${myLLVM.libclang.lib}/lib";
+          CMAKE_LLVM_DIR = "${myLLVM.libllvm.dev}/lib/cmake/llvm";
+          CMAKE_CLANG_DIR = "${myLLVM.libclang.dev}/lib/cmake/clang";
+          LLVM_CONFIG_PATH = "${myLLVM.libllvm.dev}/bin/llvm-config";
+          CLANG_PATH = "${myLLVM.clang}/bin/clang";
+          TINYCBOR_DIR = "${pkgs.tinycbor}";
+          NIX_ENFORCE_NO_NATIVE = 0; # Enable SSE instructions.
+          # Enable nix in the c2rust test suite
+          # This flag is used to tell the test scripts to look for
+          # libraries under nix paths.
+          C2RUST_USE_NIX = 1;
+          RUST_SRC_PATH = "${fenixToolchain}/lib/rustlib/src/rust/library";
+        };
+      in rec {
+        packages = {
+          default = rustPlatform.buildRustPackage (with pkgs; env // {
+            pname = "c2rust";
+            version = "0.20.0";
+            src = ./.;
+            doCheck = false; # Can use checkFlags to disable specific tests
+
+            patches = [ ./nix-tinycbor-cmake.patch ];
+
+            nativeBuildInputs =
               with pkgs; [
-                clangStdenv.cc
-                llvmPackages_14.libclang
                 pkg-config
-                fenix.packages.${system}.rust-analyzer
-                llvmPackages_14.clang
                 cmake
-                llvmPackages_14.llvm
-                llvmPackages_14.libllvm
-                openssl
                 (python3.withPackages
                   (python-pkgs:
                     with python-pkgs;
@@ -68,9 +83,43 @@
                     ]
                   )
                 )
+                myStdenv.cc
+                myLLVM.libclang
+                myLLVM.clang
+                myLLVM.llvm
+                myLLVM.libllvm
+              ];
+
+            buildInputs =
+              with pkgs; [
+                rustPlatform.bindgenHook
+                myStdenv.cc
+                myLLVM.libclang
+                myLLVM.clang
+                myLLVM.llvm
+                myLLVM.libllvm
+                tinycbor
+                openssl
                 zlib
-                (rust-bin.fromRustupToolchainFile ./rust-toolchain.toml)
+                fenixToolchain
               ];
-          };
-    });
+
+            cargoLock = {
+              lockFile = ./Cargo.lock;
+            };
+          });
+        };
+        defaultPackage = packages.default;
+
+        devShells = {
+          # Include a fixed version of clang in the development environment for testing.
+          default = pkgs.mkShell (with pkgs; env // {
+            strictDeps = true;
+            inputsFrom = [ packages.default ];
+            buildInputs = [ ];
+          });
+        };
+
+        devShell = devShells.default;
+      });
 }