GCC Rust Weekly Status Report 32

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

Milestone Progress

This report covers work completed since the 1st of November as I took the last week of the 8th off to use some vacation time. During that week, I cracked the problem of handling/managing rust’s lang-item system within gccrs; this unblocked my branch on operator overloading to demonstrate it; thanks to all the bug fixes last month, this seems to be working smoothly. Before operator overloading can be merged, the PR needs to be split up into smaller commits and rebased on top of the recent changes from the community; the DefId change comes to mind as we use this to differentiate between traits.

The community has made a significant dent into all of the lower hanging fruit of good-first-pr’s; there are many more issues like this one the way soon, so keep your eye out if you wish to find your feet to get involved.

So far, I feel like the pace of this milestone is going well, and I am still on track to be about one week over the target date. This leaves us to close out the year by testing the compiler in anger on Blake3 to see how well we get on. Aside from that, I am working on an upcoming blog post reviewing GCC Rust as a project and visiting the major accomplishments along the way in 2021, so keep your eye out for this one.

Thank you to everyone who continues to support and work on the compiler.

Monthly Community Call

We had our 8th community call on 5th November 2021 you can find the meeting notes over here: https://github.com/Rust-GCC/Reporting/blob/main/2021-11-05-community-call.md

Completed Activities

Tag ‘rust_fatal_error’ as ‘noreturn’ PR777 PR780
Add location info in AST::TypeBoundWhereClauseItem and HIR::TypeBoundWhereClauseItem PR778
Add new rust_internal_error for specific ICE’s PR779
Merge Type Checking code for enums PR781
Refactor TyTy::ADTType into one which can contain multiple variants PR781
Get rid of lambda in AST::TypePath PR783
Track inline module scopes for path module imports PR785
Save make check-rust artifacts for GHA PR787
Add new -frust-crate option to specify crate name PR788
Get rid of lambda TyTy::TupleType iterate fields PR791
Change DefId from uint64_t with bitmask into a struct PR792
Fix unhandled TypeBounds PR794
Documentation for clang-format usage PR795 PR802 PR803
Handle forward declared items within blocks PR796
Fix some missing cases of constant folding PR798

Contributors this month

Overall Task Status

Category	Last Week	This Week	Delta
TODO	99	93	-6
In Progress	12	14	+2
Completed	234	244	+10

GitHub Issues

Test Cases

Category	Last Week	This Week	Delta
Passing	4844	4931	+87
XFAIL	21	21	–

make check-rust

Bugs

Category	Last Week	This Week	Delta
TODO	22	23	+1
In Progress	3	4	+1
Completed	84	86	+2

GitHub Bugs

Milestones Progress

Milestone	Last Week	This Week	Delta	Start Date	Completion Date	Target
Data Structures 1 – Core	100%	100%	–	30th Nov 2020	27th Jan 2021	29th Jan 2021
Control Flow 1 – Core	100%	100%	–	28th Jan 2021	10th Feb 2021	26th Feb 2021
Data Structures 2 – Generics	100%	100%	–	11th Feb 2021	14th May 2021	28th May 2021
Data Structures 3 – Traits	100%	100%	–	20th May 2021	17th Sept 2021	27th Aug 2021
Control Flow 2 – Pattern Matching	55%	70%	+15%	20th Sept 2021	–	29th Nov 2021
Macros and cfg expansion	0%	0%	–	1st Dec 2021	–	28th Mar 2022
Imports and Visibility	0%	0%	–	29th Mar 2022	–	27th May 2022
Const Generics	0%	0%	–	30th May 2022	–	25th Jul 2022
Intrinsics	0%	0%	–	6th Sept 2021	–	30th Sept 2022

GitHub Milestones

Risks

Risk	Impact (1-3)	Likelihood (0-10)	Risk (I * L)	Mitigation
Rust Language Changes	3	7	21	Keep up to date with the Rust language on a regular basis
Going over target dates	3	5	15	Maintain status reports and issue tracking to stakeholders

Planned Activities

Merge lang-items work
Merge operator overloading work
Finish work on adding enum support

Detailed changelog

Refactor TyTy::ADTType

In order to support enums, we could have implemented a new TyTy module for this, to then subsequently update the typechecking code. But in a lot of ways enum’s are just another type of algebraic data type which also has the side effect of canonicalizing the flow of how we work with these types instead of inventing new paths in the compiler. The change here was that the ADT Type was originally designed for unit-structs, structs and tuple structs. But really an enum is an ADT with multiple variants and struts, tuple structs are ADT’s with a single variant and finally, a unit-struct is one with no variants. This change was rather large to decouple and refactor ADT’s into variants but has helped tackle some technical debt along the way. Thanks to @flip1995 for pointing us in this direction.

Add new rust_internal_error

This new API is designed to distinguish between internal compiler errors and actual program errors. Assertions are good but somtimes you want to be able to provide extra contextual information.

Handle forward declared items within blocks

Rust allows for Items such as functions to be declared at the bottom of a BlockExpr which can be referenced at any point within that conxtext such as: https://godbolt.org/z/PGqnz1nve

pub fn main() {
    let a;
    a = foo { a: 123, b: 456f32 };

    let mut a = 123;
    a = bar(a);

    let mut b = 456f32;
    b = bar(b);

    let aa = X;

    let bb:[i32; X];

    fn bar<T>(x: T) -> T {
        x
    }

    struct foo {
        a: i32,
        b: f32,
    };

    const X:usize = 2;
}

Fix unhandled TypeBounds

This test case qithin the rust testsuite https://github.com/rust-lang/rust/blob/d5a0c7cb036032288a4a5443b54ba061ec12ee26/src/test/ui/higher-rank-trait-bounds/hrtb-fn-like-trait-object.rs raised bugs with unhandled type bounds for TypeAlises:

type FnObject<'b> = dyn for<'a> FnLike<&'a isize, &'a isize> + 'b;

The bug here was that we had two ways in HIR to represent bounds here, and we had an opertunity to desugar our AST from two types:

AST::TraitObjectType
AST::TraitObjectTypeOneBound

Into a single HIR::TraitObjectType