January 2025 Monthly report

Overview

Thanks again to Open Source Security, inc and Embecosm for their ongoing support for this project.

Project update

We are continuing our work towards GCC 15.1, and trying to develop as many features as possible before this release. The only non-technical news this month is our Talk submission to RustWeek in the Netherlands, which you can find here - Pierre-Emmanuel and Arthur are looking forward to meeting all of you there!

We are happy to report that this month saw an impressive 48 pull-requests merged, with contributions from 10 individual developers including two new contributors, Lishin and Dylan Gardner.

Similarly to last month, we have been focusing on a few select milestones which affect a large amount of code within the Rust standard library and the Rust-for-Linux project.

We have completed the work on for-loops, and have started working on adding support for the famous “Question Mark operator”. These two milestones required an important rework of both our AST and HIR path classes, which affect almost all classes in the compiler. This rework also allowed us to continue working on Rust’s built-in derive macros, in particular Clone, Copy, Default, PartialEq and Eq.

While for-loops are simple constructs in most programming languages, they pose a real challenge in Rust and require a lot of features to be implemented properly - iterators, lang-item, type inference… After weeks of work, they are finally complete and available in gccrs. They are used in multiple areas of both the Rust standard library and Rust-for-Linux, which means our compiler’s reach has greatly increased by supporting this seemingly simple feature. If you are interested, have a look at our documentation for their implementation which goes into more detail: rust-desugar-for-loops.h

Our implementation of the Question Mark operator is almost complete, with only a couple of type inference issues remaining to close out the milestone. They are currently being worked on and will soon be merged into the compiler.

Our work on built-in derive macros also affects a large area of Rust-for-Linux and core code, as these macros are used for an important number of primitive Rust types. We added support for two new important derive macros this month, Default and PartialEq. Default enables the user to generate a ::default() function, which will create a basic instance of a type with all of its fields using a default value. This is for example used in Rust-for-Linux’s ModuleInfo struct, which is used whenever you define a new Rust module for the kernel:

#[derive(Debug, Default)] // <-- HERE!
struct ModuleInfo {
    type_: String,
    license: String,
    name: String,
    author: Option<String>,
    description: Option<String>,
    alias: Option<Vec<String>>,
    firmware: Option<Vec<String>>,
}

impl ModuleInfo {
    fn parse(it: &mut token_stream::IntoIter) -> Self {
        let mut info = ModuleInfo::default(); // <-- generated function is used HERE!

(from https://github.com/Rust-for-Linux/linux/blob/rust-next/rust/macros/module.rs#L92)

Fully supporting the ModuleInfo type means compiling its implementation, which requires us to offer a proper ::default() function for the type - which in itself requires supporting #[derive(Default)] for all of the types and subtypes contained within the ModuleInfo structure: String, Option<T>, Vec<T>…

Another example of built-in derive macro in Rust-for-Linux is PartialEq, which can be found in the implementation of the kernel memory allocation infrastructure interface. The implementiaton of the PartialEq trait through that macro enables the comparison of these allocation flags, which is required for gccrs to properly compile the Rust elements of the kernel.

Community call

We will have our next monthly community call on the 17th of February at 10am UTC. You can subscribe to our calendar to see when the next one will be held. The call is open to everyone, even if you would just like to sit-in and listen. You can also subscribe to our mailing-list or join our Zulip chat to be notified of upcoming events.

• Jitsi link
• Calendar ID: 7060a0923ffebd3cb52b1afef35a28ff7b64f05962c9af84c23b1847f1f5f894@group.calendar.google.com
• Google calendar link
• iCal link

Call for contribution

• https://github.com/Rust-GCC/gccrs/issues/2500

• https://github.com/Rust-GCC/gccrs/issues/2376

Completed Activities

• nr2.0: Remove accidental copies of resolver PR3408
• Fix an issue with ForeverStack::dfs_rib PR3406
• Resolve lang-item PathInExpressions in nr2.0 late resolver PR3404
• lang-items: Add structural_{peq, teq} PR3401
• Do not warn about unused fields if they start with ‘_’ PR3400
• Add derive(Debug) stub PR3398
• Update upload-artifact to v4 PR3387
• ast: builder: Add Return expression builder PR3386
• ast: Add new Expr::Kinds PR3385
• lang-items: Add From::from PR3384
• gccrs: add new -frust-overflow-checks to control overflow checks PR3383
• gccrs: catch missing guard for optional result PR3380
• backend: Allow anything as a match scrutinee PR3379
• Prepare lang-item {AST, HIR}::PathInExpressions PR3378
• Check for type paths nr2.0 can’t handle yet PR3377
• gccrs: add support for ref literal patterns PR3376
• lang-items: Add Result and Try lang items PR3375
• Add receiver lang item PR3374
• Nr2 closure captures PR3373
• Add basic handling for auto-traits PR3370
• derive(Copy): Improve bounds when deriving Copy PR3369
• Improve derive(Clone) for generic types PR3367
• Refactor lang item paths PR3366
• gccrs: Add missing name resolution to static items in blocks PR3365
• nr2.0: Early resolve pending eager macro invocations PR3364
• Remove dead code related to external functions PR3363
• Revert “refactor all attribute functions in rust-collect-lang-items.cc” PR3361
• gccrs: match arms are a LUB PR3360
• nr2.0: Resolve Self inside impl blocks PR3359
• gccrs: fix ICE with hir dump on closure PR3358
• gccrs: cleanup our enum type layout to be closer to rustc PR3357
• gccrs: fix ICE in borrows to invalid expressions PR3356
• gccrs: add support for lang_item eq and PartialEq trait PR3347
• Finish derive(Clone) for enums PR3343
• refactor all attribute functions in rust-collect-lang-items.cc PR3338
• nr2.0: Improve default and top-level resolvers PR3332
• Visit the trait paths of trait implementations PR3331
• Allow float type to be casted as integer type PR3319
• gccrs: improve mutability checks PR3311
• Fix nr2 unit struct PR3299
• Fix bug in type resolution of paths PR3277
• Fix rust breakage with nr2 PR3266
• Add ForeverStackStore PR3251
• Infer crate name after file opening PR3146
• Add option_env support PR3094
• testsuite: Fix missing handling of little endian. PR2805
• Add try intrinsics PR2614

Contributors this month

• Lishin (new contributor!)
• Dylan Gardner (new contributor!)
• liushuyu
• Liam Naddell
• Nobel Singh
• Owen Avery
• Marc Poulhiès
• Thomas Schwinge
• Philip Herron
• Pierre-Emmanuel Patry
• Arthur Cohen

Overall Task Status

Bugs

Test Cases

Milestones Progress

Planned Activities

• Implement remaining built-in derive macros
• Improve our process for updating our github repository with upstream GCC

Risks

We have now entered Stage 3 of GCC development, and all of the patches we needed to get upstreamed have been upstreamed. The risk that were outlined here are no longer present, and we are focusing on getting as many features implemented and upstreamed as possible.