Provide Rust wrapper for memory resouces

[eclipse-impl]

This allows Rust applications that interface with C++ to obtain memory resources to pass back to C++, such that the C++ code will allocate from them, allowing for controlling the memory allocation between the languages.

[github-actions]

The created documentation from the pull request is available at: docu-html

[pawelrutkaq]

@arkjedrz have a look please

[Copilot]

Pull request overview

This PR introduces a new score/language/rust/memres Rust crate and accompanying C++ FFI layer to let Rust code create/own score::cpp::pmr::memory_resource instances and pass them back into C++ so allocations can be controlled across the language boundary (including a “hermetic” no-heap-fallback mode).

Changes:

• Add a C++ handle hierarchy (MemResHandle + concrete implementations) and extern "C" API for creating/destroying PMR resources and retrieving the underlying memory_resource*.
• Add a safe Rust wrapper API (MemoryResource, ResourceKind, PoolOptions) plus unit tests and an example demonstrating hermetic monotonic behavior.
• Integrate the crate into Bazel + Cargo workspace, and bump the Rust toolchains Bazel dep version.

Reviewed changes

Copilot reviewed 18 out of 20 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
score/language/rust/memres/test/memres_test.cpp	Adds C++ gtest coverage for handle creation, monotonic hermetic abort, and non-hermetic fallback.
score/language/rust/memres/test/memres_rust_test.rs	Adds Rust unit tests exercising the Rust API and end-to-end FFI path.
score/language/rust/memres/src/lib.rs	Implements the Rust API wrapper, FFI bindings, and lifetime-bound pointer wrapper.
score/language/rust/memres/README.md	Documents design, safety/lifetime invariants, hermetic behavior, and Bazel targets.
score/language/rust/memres/example/main.rs	Example binary demonstrating hermetic monotonic behavior and abort-on-overflow.
score/language/rust/memres/example/example_helpers.h	Declares C ABI helpers used by the example and Rust tests.
score/language/rust/memres/example/example_helpers.cpp	Implements the C ABI helpers for allocating/filling a PMR-backed C++ vector.
score/language/rust/memres/example/BUILD	Adds Bazel targets for the example and helper library.
score/language/rust/memres/cpp/memory_resource_handle.h	Declares the handle class hierarchy owning PMR resources and upstream guard.
score/language/rust/memres/cpp/memory_resource_handle.cpp	Implements handle constructors and resource accessors.
score/language/rust/memres/cpp/guarded_upstream.h	Declares the upstream memory_resource enforcing hermetic/heap-fallback policy.
score/language/rust/memres/cpp/guarded_upstream.cpp	Implements guarded upstream allocate/deallocate and logging/abort behavior.
score/language/rust/memres/cpp/ffi.h	Declares the plain-C API consumed by Rust and C++ tests.
score/language/rust/memres/cpp/ffi.cpp	Implements the C API and bridges to the handle classes.
score/language/rust/memres/Cargo.toml	Adds the new Rust crate manifest.
score/language/rust/memres/BUILD	Adds Bazel cc/rust targets for the library and unit tests.
MODULE.bazel.lock	Updates lockfile due to Rust toolchain dep bump (and related module resolution changes).
MODULE.bazel	Bumps score_toolchains_rust dev dependency version.
Cargo.toml	Adds memres to workspace members/default-members and workspace dependency map.
Cargo.lock	Records the new workspace crate and updates some transitive crate versions.

Suppressed comments (1)

score/language/rust/memres/cpp/guarded_upstream.cpp:35

• The warning log message concatenates tokens without spaces (e.g. "requested10bytes"), reducing its usefulness for diagnostics.

    score::mw::log::LogWarn("memres") << "Memory resource exhausted: requested" << bytes << "bytes with alignment"
                                      << alignment << ". Falling back to system heap.";

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[eclipse-impl]

In principle, this would be a false positive for MemoryResource<Local>, which is Local's purpose of usage on this PR, because MemoryResource carries a mutable pointer and is thus not Send + Sync. But it's true that someone could have another type with threading information, and reuse these definitions, say:

struct Borrower<'a, S> {
    _resource: core::marker::PhantomData<&'a S>,
}

In this case, Borrower<'_, Local> would be Send + Sync and therefore the original semantic would not be achieved, as pointed out by the AI. Therefore, I followed its suggestion and updated the code to explicitly state that Local shall never be Send + Sync.

[eclipse-impl]

This is not the case. The interface allows for Rust programs to interface with C++ code that use the memory resources. As the Rust interface does not export set_default_resource, there's no way for a Rust application to overload the default behavior.

[eclipse-impl]

This is not the case. The interface allows for Rust programs to interface with C++ code that use the memory resources. As the Rust interface does not export set_default_resource, there's no way for a Rust application to overload the default behavior.

[eclipse-impl]

This is not the case, the elements separator is added by the backend.

[4og]

The "Rust Coverage (Demo)" workflow fails in this PR, and it looks like an issue in the coverage toolchain and not the code.

thread 'rustc' (17424) panicked at ferrocene/tools/symbol-report/src/main.rs:44:41:
called `Option::unwrap()` on a `None` value

We disabled the workflow in baselibs for now. There is ongoing work to improve the coverage tooling, and I hope once it's done, we can reenable the coverage for rust. eclipse-score/tooling#394