rust: implement Reloc macro

Author: pawelrutkaq

MODULE.bazel

@@ -98,7 +98,7 @@ bazel_dep(name = "googletest", version = "1.17.0.bcr.2")
 bazel_dep(name = "google_benchmark", version = "1.9.4")
 bazel_dep(name = "rules_rust", version = "0.61.0")
 bazel_dep(name = "buildifier_prebuilt", version = "8.2.0.2")
-bazel_dep(name = "score_crates", version = "0.0.5", repo_name = "crate_index")
+bazel_dep(name = "score_crates", version = "0.0.6", repo_name = "crate_index")
 
 bazel_dep(name = "boost.program_options", version = "1.87.0")
 bazel_dep(name = "download_utils", version = "1.0.1")

score/mw/com/example/com-api-example/com-api-gen/com_api_gen.rs

@@ -15,13 +15,13 @@ use com_api::{
     Consumer, Interface, OfferedProducer, Producer, Publisher, Reloc, Runtime, Subscriber,
 };
 
-#[derive(Debug)]
+#[derive(Debug, Reloc)]
+#[repr(C)]
 pub struct Tire {}
-unsafe impl Reloc for Tire {}
 
-#[derive(Debug)]
+#[derive(Debug, Reloc)]
+#[repr(C)]
 pub struct Exhaust {}
-unsafe impl Reloc for Exhaust {}
 
 pub struct VehicleInterface {}
 

score/mw/com/impl/rust/com-api/com-api-concept-macros/BUILD

@@ -0,0 +1,31 @@
+# *******************************************************************************
+# Copyright (c) 2025 Contributors to the Eclipse Foundation
+#
+# See the NOTICE file(s) distributed with this work for additional
+# information regarding copyright ownership.
+#
+# This program and the accompanying materials are made available under the
+# terms of the Apache License Version 2.0 which is available at
+# https://www.apache.org/licenses/LICENSE-2.0
+#
+# SPDX-License-Identifier: Apache-2.0
+# *******************************************************************************
+load("@rules_rust//rust:defs.bzl", "rust_proc_macro", "rust_doc_test")
+
+rust_proc_macro(
+    name = "com-api-concept-macros",
+    srcs = ["lib.rs"],
+    crate_name = "com_api_concept_macros",
+    visibility = [
+        "//visibility:public",
+    ],
+    deps = [
+        "@crate_index//:syn",
+        "@crate_index//:quote",
+    ],
+)
+
+rust_doc_test(
+    name = "com-api-concept-macros-tests",
+    crate = ":com-api-concept-macros",
+)

score/mw/com/impl/rust/com-api/com-api-concept-macros/lib.rs

@@ -0,0 +1,247 @@
+use proc_macro::TokenStream;
+use quote::quote;
+use syn::{parse_macro_input, parse_quote, Data, DeriveInput, Fields, Generics, Meta, Type};
+
+///
+/// Derive macro for the `Reloc` trait. This macro automatically implements the `Reloc` trait
+/// for structs, ensuring that all field types also implement `Reloc`. This also requires that the
+/// struct is marked with `#[repr(C)]`.
+///
+#[proc_macro_derive(Reloc)]
+pub fn derive_reloc(input: TokenStream) -> TokenStream {
+    let input_args = parse_macro_input!(input as DeriveInput);
+    let ident_name = &input_args.ident;
+
+    // Ensure #[repr(C)] on the struct itself
+    if !has_repr_c(&input_args.attrs) {
+        return syn::Error::new_spanned(
+            &ident_name,
+            "The #[derive(Reloc)] macro requires #[repr(C)] on the type",
+        )
+        .to_compile_error()
+        .into();
+    }
+
+    let mut generics = create_bounds_with_reloc(input_args.generics.clone());
+
+    // Collect field types. Since we cannot check if given field type has implemented given trait we will use compiler
+    // to check that generating trait bounds on fields like below:
+    //
+    // struct Example {
+    //     field1: SomeType,
+    //     field2: AnotherType,
+    // }
+    // unsafe impl Reloc for Example where SomeType: Reloc, AnotherType: Reloc {}
+    //
+    let field_types = match collect_field_types(&input_args.data){
+        Ok(types) => types,
+        Err(()) => return syn::Error::new_spanned(
+            &ident_name,
+            "The #[derive(Reloc)] macro is supported only for enums(C like), structs and tuple structs",
+        )
+        .to_compile_error()
+        .into(),
+    };
+
+    {
+        let where_clause_ref = generics.make_where_clause();
+        for ty in field_types {
+            where_clause_ref.predicates.push(parse_quote!(#ty: Reloc));
+        }
+    }
+
+    // Create pieces for final implementation
+    let (impl_generics, type_generics, where_clause) = generics.split_for_impl();
+
+    let expanded = quote! {
+        unsafe impl #impl_generics Reloc for #ident_name #type_generics #where_clause {}
+    };
+
+    expanded.into()
+}
+
+/// Add `T: Reloc` bounds to all generic parameters
+fn create_bounds_with_reloc(mut generics: Generics) -> Generics {
+    for param in generics.type_params_mut() {
+        param.bounds.push(parse_quote!(Reloc));
+    }
+    generics
+}
+
+/// Check for #[repr(C)] existence
+fn has_repr_c(attrs: &[syn::Attribute]) -> bool {
+    for attr in attrs {
+        if attr.path().is_ident("repr") {
+            if let Meta::List(list) = &attr.meta {
+                let tokens = list.tokens.to_string();
+                if tokens.split(',').any(|t| t.trim() == "C") {
+                    return true;
+                }
+            }
+        }
+    }
+    false
+}
+
+/// Collect field types, skipping generic parameters and primitives
+fn collect_field_types<'a>(data: &'a Data) -> Result<Vec<&'a Type>, ()> {
+    let mut out = Vec::new();
+
+    match data {
+        Data::Struct(data_struct) => {
+            out = match &data_struct.fields {
+                Fields::Named(fields) => fields.named.iter().map(|f| &f.ty).collect(),
+                Fields::Unnamed(fields) => fields.unnamed.iter().map(|f| &f.ty).collect(),
+                Fields::Unit => Vec::new(),
+            };
+        }
+        Data::Enum(data_enum) => {
+            if !data_enum
+                .variants
+                .iter()
+                .all(|variant| matches!(variant.fields, Fields::Unit))
+            {
+                return Err(());
+            }
+        }
+        Data::Union(_) => return Err(()),
+    };
+
+    Ok(out)
+}
+
+// Use doctest to test failed compilations and successful ones
+
+/// ```
+/// pub unsafe trait Reloc {}
+/// use com_api_concept_macros::Reloc;
+///
+/// #[derive(Reloc)]
+/// #[repr(C)]
+/// pub struct RelocType<T> { t : T}
+///
+/// #[derive(Reloc)]
+/// #[repr(C)]
+/// pub struct RelocTypeTwoGen<T, D> { t : T, d: D}
+/// ```
+#[cfg(doctest)]
+fn reloc_works_on_generic_types() {}
+
+/// ```
+/// pub unsafe trait Reloc {}
+/// use com_api_concept_macros::Reloc;
+///
+/// #[derive(Reloc)]
+/// #[repr(C)]
+/// enum EnumPlanType {
+///     A,
+///     B,
+///     C
+/// }
+/// ```
+#[cfg(doctest)]
+fn reloc_works_on_c_like_enums() {}
+
+/// ```
+/// pub unsafe trait Reloc {}
+/// use com_api_concept_macros::Reloc;
+///
+/// #[derive(Reloc)]
+/// #[repr(C)]
+/// struct StructTag{}
+/// ```
+#[cfg(doctest)]
+fn reloc_works_on_unit() {}
+
+/// ```
+/// pub unsafe trait Reloc {}
+/// unsafe impl Reloc for u32{}
+/// unsafe impl Reloc for u64{}
+///
+/// use com_api_concept_macros::Reloc;
+///
+/// #[derive(Reloc)]
+/// #[repr(C)]
+/// pub struct RelocType<T> { t : T}
+///
+/// #[derive(Reloc)]
+/// #[repr(C)]
+/// pub struct StructType {
+///     a: u32,
+///     b: u64,
+///     f: RelocType<u64>
+/// }
+/// ```
+#[cfg(doctest)]
+fn reloc_works_on_structs() {}
+
+/// ```
+/// pub unsafe trait Reloc {}
+/// unsafe impl Reloc for u32{}
+/// unsafe impl Reloc for u64{}
+///
+/// use com_api_concept_macros::Reloc;
+///
+/// #[derive(Reloc)]
+/// #[repr(C)]
+/// pub struct RelocType<T> { t : T}
+///
+/// #[derive(Reloc)]
+/// #[repr(C)]
+/// pub struct TupleStructType( u32, u64, RelocType<u64> );
+/// ```
+#[cfg(doctest)]
+fn reloc_works_on_tuples() {}
+
+// Failure cases
+
+/// ```compile_fail
+/// pub unsafe trait Reloc {}
+/// use com_api_concept_macros::Reloc;
+///
+/// #[derive(Reloc)]
+/// #[repr(C)]
+/// enum EnumPlanType {
+///     A(u32),
+///     B,
+///     C
+/// }
+/// ```
+#[cfg(doctest)]
+fn reloc_fail_on_non_c_like_enums() {}
+
+/// ```compile_fail
+/// pub unsafe trait Reloc {}
+/// unsafe impl Reloc for u32{}
+///
+/// use com_api_concept_macros::Reloc;
+///
+/// #[derive(Reloc)]
+/// #[repr(C)]
+/// pub struct RelocType<T> { t : T}
+///
+/// #[derive(Reloc)]
+/// #[repr(C)]
+/// pub struct StructType {
+///     a: u32,
+///     b: u64,
+///     f: RelocType<u64>
+/// }
+/// ```
+#[cfg(doctest)]
+fn reloc_fails_if_member_is_not_reloc_on_struct() {}
+
+/// ```compile_fail
+/// pub unsafe trait Reloc {}
+/// use com_api_concept_macros::Reloc;
+///
+/// #[derive(Reloc)]
+/// #[repr(C)]
+/// pub struct RelocType<T> { t : T}
+///
+/// #[derive(Reloc)]
+/// #[repr(C)]
+/// pub struct ContainsNonRelocType(RelocType<u64>);
+/// ```
+#[cfg(doctest)]
+fn reloc_fails_on_generic_types_that_do_not_impl_reloc() {}

score/mw/com/impl/rust/com-api/com-api-concept/BUILD

@@ -23,6 +23,9 @@ rust_library(
         "//visibility:public",  # platform_only
     ],
     deps = [],
+    proc_macro_deps = [
+        "//score/mw/com/impl/rust/com-api/com-api-concept-macros",
+    ],
 )
 
 rust_test(

score/mw/com/impl/rust/com-api/com-api-concept/reloc.rs

@@ -27,6 +27,8 @@
 /// is unsafe for now. The expectation is that very few users ever need to implement this manually.
 pub unsafe trait Reloc {}
 
+pub use com_api_concept_macros::Reloc;
+
 unsafe impl Reloc for () {}
 unsafe impl Reloc for u8 {}
 unsafe impl Reloc for u16 {}

score/mw/com/impl/rust/com-api/com-api/com_api.rs

@@ -22,3 +22,4 @@ pub use com_api_concept::{
     Publisher, Reloc, Result, Runtime, SampleContainer, SampleMaybeUninit, SampleMut,
     ServiceDiscovery, Subscriber, Subscription,
 };
+