rust support in libutil via rust-monocrate

Co-authored-by: Jade Lovelace <jadel@mercury.com>

Change-Id: I026f271b07c9e27012f9ee1c16a2a1f4ba7f6ba3

Cargo.lock

@@ -39,6 +39,10 @@ dependencies = [
  "rowan",
 ]
 
+[[package]]
+name = "lixutil-rs"
+version = "0.0.0"
+
 [[package]]
 name = "once_cell"
 version = "1.19.0"

Cargo.toml

@@ -1,6 +1,6 @@
 [workspace]
 resolver = "2"
-members = ["lix/lix-doc"]
+members = ["lix/lix-doc", "lix/libutil"]
 
 [workspace.package]
 edition = "2021"

lix/libutil/Cargo.toml

@@ -0,0 +1,13 @@
+# Note: this is not really intended to actually do anything with Cargo, it
+# exists to make Cargo manage dependencies in a workspace across lix-doc and
+# liblixrust
+#
+# It is highly likely it will not actually pass build, especially as the build
+# system gets more anti-Cargo.
+
+[package]
+name = "lixutil-rs"
+edition.workspace = true
+
+[lib]
+path = "lib.rs"

lix/libutil/cbindgen.toml

@@ -0,0 +1,2 @@
+language = "C++"
+namespace = "nix"

lix/libutil/lib.rs

@@ -0,0 +1,14 @@
+#[repr(C)]
+pub struct TestMultiplyArgs {
+    pub a: u64,
+    pub b: u64,
+}
+
+#[no_mangle]
+pub extern "C" fn test_multiply(args: TestMultiplyArgs) -> u64 {
+    args.a * args.b
+}
+
+pub mod exports {
+    pub use super::test_multiply;
+}

lix/libutil/meson.build

@@ -344,6 +344,10 @@ dependencies = [
   nlohmann_json,
   openssl,
   libatomic,
+
+  # NOTE: this is secretly rust-monocrate in a trenchcoat.
+  # See that directory's README for more details.
+  liblixutil_rs,
 ]
 
 libutil_temp = library(
@@ -422,6 +426,8 @@ liblixutil = declare_dependency(
     libarchive,
     nlohmann_json,
     libatomic,
+    # This is secretly rust-monocrate + the generated header.
+    liblixutil_rs,
   ],
   link_with : libutil
 )

lix/meson.build

@@ -25,8 +25,54 @@ install_headers(config_h, subdir : 'lix')
 # Subcomponents: these link into artifacts themselves, and have interdependencies.
 subdir('lix-doc')
 
+# We manage libutil's Rust components here, because subdir(rust-monocrate)
+# needs libutil's Rust components, and subdir(libutil) needs rust-monocrate.
+# FIXME?: Should libutil-rs just be in a separate directory from libutil, then?
+libutil_rs_sources = files(
+  'libutil/lib.rs',
+)
+libutil_rs = static_library(
+  'lixutil_rs',
+  sources : libutil_rs_sources,
+  rust_args : [
+    # Will be empty if we're linking statically.
+    rust_dynamic_args,
+    # Will no-op if we're linking statically.
+    '-C', f'link-arg=-Wl,@soname_arg@,liblixutil_rs.@dylib_suffix@',
+  ],
+)
+libutil_rs_gen_h = custom_target(
+  'libutil-rs.gen.hh',
+  input : [
+    files('libutil/cbindgen.toml'),
+    libutil_rs_sources,
+  ],
+  output : ['libutil-rs.gen.hh'],
+  command : [
+    cbindgen,
+    '--config',
+    '@INPUT0@',
+    '--output',
+    '@OUTPUT0@',
+    '--',
+    '@INPUT1@',
+  ],
+)
+# For rust-monocrate.
+liblixutil_rs_internal = declare_dependency(
+  link_with : libutil_rs,
+)
+
 subdir('rust-monocrate')
 
+# NOW we can create the dependency object anything that actually wants to use liblixutil_rs,
+# because liblixutil_rs is secretly rust-monocrate in a trenchcoat.
+# `library('lixutil')` and `executable('liblixutil-tests')` depend on this.
+liblixutil_rs = declare_dependency(
+  link_with : rust_monocrate,
+  sources : [libutil_rs_gen_h],
+)
+
 # liblix_doc is actually rust-monocrate in a trenchcoat.
 liblix_doc = declare_dependency(
   link_with : rust_monocrate,

lix/rust-monocrate/Cargo.toml

@@ -6,3 +6,4 @@ edition.workspace = true
 [lib]
 crate-type = ["staticlib"]
 lix-doc = { path = "../lix-doc" }
+lixutil_rs = { path = "../libutil_rs" }

lix/rust-monocrate/meson.build

@@ -10,6 +10,7 @@ rust_monocrate = static_library(
   sources : rust_monocrate_sources,
   dependencies : [
     liblix_doc_internal,
+    liblixutil_rs_internal,
     rnix,
     rowan,
   ],

lix/rust-monocrate/src/lib.rs

@@ -10,3 +10,4 @@
 //!
 //! It re-exports all the symbols that should be exported to C++.
 pub use lix_doc::*;
+pub use lixutil_rs::*;

tests/unit/libutil/rust.cc

@@ -0,0 +1,15 @@
+#include "lix/libutil-rs.gen.hh"
+#include <gtest/gtest.h>
+
+namespace nix {
+    TEST(rustSupport, testMultiplyArgs) {
+        TestMultiplyArgs const args{
+            .a = 20,
+            .b = 5,
+        };
+
+        uint64_t const product = test_multiply(args);
+
+        ASSERT_EQ(product, 20 * 5);
+    }
+}

tests/unit/meson.build

@@ -69,6 +69,7 @@ libutil_tests_sources = files(
   'libutil/paths-setting.cc',
   'libutil/pool.cc',
   'libutil/references.cc',
+  'libutil/rust.cc',
   'libutil/serialise.cc',
   'libutil/suggestions.cc',
   'libutil/tarfile.cc',