Stabilize `repr128` #138285

beetrees · 2025-03-09T20:09:47Z

Stabilisation report

The repr128 feature (tracking issue) allows the use of #[repr(u128)] and #[repr(i128)] on enums in the same way that other primitive representations such as #[repr(u64)] can be used. For example:

#[repr(u128)]
enum Foo {
    One = 1,
    Two,
    Big = u128::MAX,
}

#[repr(i128)]
enum Bar {
    HasThing(u16) = 42,
    HasSomethingElse(i64) = u64::MAX as i128 + 1,
    HasNothing,
}

This is the final part of adding 128-bit integers to Rust (RFC 1504); all other parts of 128-bit integer support were stabilised in #49101 back in 2018.

From a design perspective, #[repr(u128)]/#[repr(i128)] function like #[repr(u64)]/#[repr(i64)] but for 128-bit integers instead of 64-bit integers. The only differences are:

FFI safety: as u128/i128 are not currently considered FFI safe, neither are #[repr(u128)]/#[repr(i128)] enums (I discovered this wasn't the case while drafting this stabilisation report, so I have submitted Add #[repr(u128)]/#[repr(i128)] enums to improper_ctypes_definitions #138282 to fix this).
Debug info: while none of the major debuggers currently support 128-bit integers, as of LLVM 20 rustc will emit valid debuginfo for both DWARF and PDB (PDB makes use of the same natvis that is also used for all enums with fields, whereas DWARF has native support).

Tests for #[repr(u128)]/#[repr(i128)] enums include:

ui/enum-discriminant/repr128.rs: checks that 128-bit enum discriminants have the correct values.
debuginfo/msvc-pretty-enums.rs: checks the PDB debuginfo is correct.
run-make/repr128-dwarf: checks the DWARF debuginfo is correct.

Stabilising this feature does not require any changes to the Rust Reference as the documentation on primitive representations already includes u128 and i128.

Closes #56071
Closes rust-lang/reference#1368

r? lang

@rustbot label +I-lang-nominated +T-lang

rustbot · 2025-03-09T20:09:55Z

Some changes occurred in tests/rustdoc-json

cc @aDotInTheVoid

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

This PR modifies run-make tests.

cc @jieyouxu

…3, r=compiler-errors triagebot.toml: Don't label `test/rustdoc-json` as A-rustdoc-search (… Followup to rust-lang#137958. I managed to miss a place, as shown by the questionable labeling of rust-lang#138285.

traviscross · 2025-03-10T07:47:41Z

@rfcbot fcp merge

Clearly, I think, we want this if we're sure it's ready (if nothing else from the perspective of consistency and minimizing caveats in our language specification). Let's start FCP, ping people, and file a concern to order this with respect to #137306.

rfcbot · 2025-03-10T07:47:43Z

Team member @traviscross has proposed to merge this. The next step is review by the rest of the tagged team members:

Concerns:

~~decide-on-137306~~ resolved by Stabilize repr128 #138285 (comment)

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

cc @rust-lang/lang-advisors: FCP proposed for lang, please feel free to register concerns.
See this document for info about what commands tagged team members can give me.

traviscross · 2025-03-10T07:48:24Z

cc @rust-lang/opsem @rust-lang/wg-llvm @wesleywiser @workingjubilee @chorman0773 @RalfJung @bjorn3 @ehuss

bjorn3 · 2025-05-28T09:01:00Z

In any case, based on reading the tracking issue, I do believe all blockers are resolved.

@bors r=traviscross,bjorn3

bors · 2025-05-28T09:01:03Z

📌 Commit 30f13ca has been approved by traviscross,bjorn3

It is now in the queue for this repository.

…ross,bjorn3 Stabilize `repr128` ## Stabilisation report The `repr128` feature ([tracking issue](rust-lang#56071)) allows the use of `#[repr(u128)]` and `#[repr(i128)]` on enums in the same way that other primitive representations such as `#[repr(u64)]` can be used. For example: ```rust #[repr(u128)] enum Foo { One = 1, Two, Big = u128::MAX, } #[repr(i128)] enum Bar { HasThing(u16) = 42, HasSomethingElse(i64) = u64::MAX as i128 + 1, HasNothing, } ``` This is the final part of adding 128-bit integers to Rust ([RFC 1504](https://rust-lang.github.io/rfcs/1504-int128.html)); all other parts of 128-bit integer support were stabilised in rust-lang#49101 back in 2018. From a design perspective, `#[repr(u128)]`/`#[repr(i128)]` function like `#[repr(u64)]`/`#[repr(i64)]` but for 128-bit integers instead of 64-bit integers. The only differences are: - FFI safety: as `u128`/`i128` are not currently considered FFI safe, neither are `#[repr(u128)]`/`#[repr(i128)]` enums (I discovered this wasn't the case while drafting this stabilisation report, so I have submitted rust-lang#138282 to fix this). - Debug info: while none of the major debuggers currently support 128-bit integers, as of LLVM 20 `rustc` will emit valid debuginfo for both DWARF and PDB (PDB makes use of the same natvis that is also used for all enums with fields, whereas DWARF has native support). Tests for `#[repr(u128)]`/`#[repr(i128)]` enums include: - [ui/enum-discriminant/repr128.rs](https://github.com/rust-lang/rust/blob/385970f0c1fd0c09bac426b02f38300c0b1ba9a2/tests/ui/enum-discriminant/repr128.rs): checks that 128-bit enum discriminants have the correct values. - [debuginfo/msvc-pretty-enums.rs](https://github.com/rust-lang/rust/blob/385970f0c1fd0c09bac426b02f38300c0b1ba9a2/tests/debuginfo/msvc-pretty-enums.rs): checks the PDB debuginfo is correct. - [run-make/repr128-dwarf](https://github.com/rust-lang/rust/blob/385970f0c1fd0c09bac426b02f38300c0b1ba9a2/tests/run-make/repr128-dwarf/rmake.rs): checks the DWARF debuginfo is correct. Stabilising this feature does not require any changes to the Rust Reference as [the documentation on primitive representations](https://doc.rust-lang.org/nightly/reference/type-layout.html#r-layout.repr.primitive.intro) already includes `u128` and `i128`. Closes rust-lang#56071 Closes rust-lang/reference#1368 r? lang `@rustbot` label +I-lang-nominated +T-lang

jieyouxu · 2025-05-28T13:50:03Z

I think you missed a feature gate in

rust/tests/ui/lint/lint-ctypes-enum.rs

Line 5 in 77101fe

#![feature(repr128)]

Rollup failure: #141688 (comment)

@bors r-

beetrees · 2025-05-28T14:16:39Z

Fixed with a rebase.

@rustbot ready

bjorn3 · 2025-05-28T14:31:31Z

@bors r=traviscross,bjorn3

bors · 2025-05-28T14:31:33Z

📌 Commit 467eeab has been approved by traviscross,bjorn3

It is now in the queue for this repository.

…ross,bjorn3 Stabilize `repr128` ## Stabilisation report The `repr128` feature ([tracking issue](rust-lang#56071)) allows the use of `#[repr(u128)]` and `#[repr(i128)]` on enums in the same way that other primitive representations such as `#[repr(u64)]` can be used. For example: ```rust #[repr(u128)] enum Foo { One = 1, Two, Big = u128::MAX, } #[repr(i128)] enum Bar { HasThing(u16) = 42, HasSomethingElse(i64) = u64::MAX as i128 + 1, HasNothing, } ``` This is the final part of adding 128-bit integers to Rust ([RFC 1504](https://rust-lang.github.io/rfcs/1504-int128.html)); all other parts of 128-bit integer support were stabilised in rust-lang#49101 back in 2018. From a design perspective, `#[repr(u128)]`/`#[repr(i128)]` function like `#[repr(u64)]`/`#[repr(i64)]` but for 128-bit integers instead of 64-bit integers. The only differences are: - FFI safety: as `u128`/`i128` are not currently considered FFI safe, neither are `#[repr(u128)]`/`#[repr(i128)]` enums (I discovered this wasn't the case while drafting this stabilisation report, so I have submitted rust-lang#138282 to fix this). - Debug info: while none of the major debuggers currently support 128-bit integers, as of LLVM 20 `rustc` will emit valid debuginfo for both DWARF and PDB (PDB makes use of the same natvis that is also used for all enums with fields, whereas DWARF has native support). Tests for `#[repr(u128)]`/`#[repr(i128)]` enums include: - [ui/enum-discriminant/repr128.rs](https://github.com/rust-lang/rust/blob/385970f0c1fd0c09bac426b02f38300c0b1ba9a2/tests/ui/enum-discriminant/repr128.rs): checks that 128-bit enum discriminants have the correct values. - [debuginfo/msvc-pretty-enums.rs](https://github.com/rust-lang/rust/blob/385970f0c1fd0c09bac426b02f38300c0b1ba9a2/tests/debuginfo/msvc-pretty-enums.rs): checks the PDB debuginfo is correct. - [run-make/repr128-dwarf](https://github.com/rust-lang/rust/blob/385970f0c1fd0c09bac426b02f38300c0b1ba9a2/tests/run-make/repr128-dwarf/rmake.rs): checks the DWARF debuginfo is correct. Stabilising this feature does not require any changes to the Rust Reference as [the documentation on primitive representations](https://doc.rust-lang.org/nightly/reference/type-layout.html#r-layout.repr.primitive.intro) already includes `u128` and `i128`. Closes rust-lang#56071 Closes rust-lang/reference#1368 r? lang `@rustbot` label +I-lang-nominated +T-lang

Rollup of 7 pull requests Successful merges: - #125087 (Optimize `Seek::stream_len` impl for `File`) - #133823 (Use `cfg_attr_trace` in AST with a placeholder attribute for accurate suggestion) - #138285 (Stabilize `repr128`) - #139994 (add `CStr::display`) - #141477 (Path::with_extension: show that it adds an extension where one did no…) - #141533 (clean up old rintf leftovers) - #141693 (Subtree update of `rust-analyzer`) r? `@ghost` `@rustbot` modify labels: rollup

…ross,bjorn3 Stabilize `repr128` ## Stabilisation report The `repr128` feature ([tracking issue](rust-lang#56071)) allows the use of `#[repr(u128)]` and `#[repr(i128)]` on enums in the same way that other primitive representations such as `#[repr(u64)]` can be used. For example: ```rust #[repr(u128)] enum Foo { One = 1, Two, Big = u128::MAX, } #[repr(i128)] enum Bar { HasThing(u16) = 42, HasSomethingElse(i64) = u64::MAX as i128 + 1, HasNothing, } ``` This is the final part of adding 128-bit integers to Rust ([RFC 1504](https://rust-lang.github.io/rfcs/1504-int128.html)); all other parts of 128-bit integer support were stabilised in rust-lang#49101 back in 2018. From a design perspective, `#[repr(u128)]`/`#[repr(i128)]` function like `#[repr(u64)]`/`#[repr(i64)]` but for 128-bit integers instead of 64-bit integers. The only differences are: - FFI safety: as `u128`/`i128` are not currently considered FFI safe, neither are `#[repr(u128)]`/`#[repr(i128)]` enums (I discovered this wasn't the case while drafting this stabilisation report, so I have submitted rust-lang#138282 to fix this). - Debug info: while none of the major debuggers currently support 128-bit integers, as of LLVM 20 `rustc` will emit valid debuginfo for both DWARF and PDB (PDB makes use of the same natvis that is also used for all enums with fields, whereas DWARF has native support). Tests for `#[repr(u128)]`/`#[repr(i128)]` enums include: - [ui/enum-discriminant/repr128.rs](https://github.com/rust-lang/rust/blob/385970f0c1fd0c09bac426b02f38300c0b1ba9a2/tests/ui/enum-discriminant/repr128.rs): checks that 128-bit enum discriminants have the correct values. - [debuginfo/msvc-pretty-enums.rs](https://github.com/rust-lang/rust/blob/385970f0c1fd0c09bac426b02f38300c0b1ba9a2/tests/debuginfo/msvc-pretty-enums.rs): checks the PDB debuginfo is correct. - [run-make/repr128-dwarf](https://github.com/rust-lang/rust/blob/385970f0c1fd0c09bac426b02f38300c0b1ba9a2/tests/run-make/repr128-dwarf/rmake.rs): checks the DWARF debuginfo is correct. Stabilising this feature does not require any changes to the Rust Reference as [the documentation on primitive representations](https://doc.rust-lang.org/nightly/reference/type-layout.html#r-layout.repr.primitive.intro) already includes `u128` and `i128`. Closes rust-lang#56071 Closes rust-lang/reference#1368 r? lang ``@rustbot`` label +I-lang-nominated +T-lang

Rollup of 8 pull requests Successful merges: - #125087 (Optimize `Seek::stream_len` impl for `File`) - #138285 (Stabilize `repr128`) - #139994 (add `CStr::display`) - #141477 (Path::with_extension: show that it adds an extension where one did no…) - #141533 (clean up old rintf leftovers) - #141690 (Add `rustc_diagnostic_item` to `sys::Mutex` methods) - #141693 (Subtree update of `rust-analyzer`) - #141702 (Add eholk to compiler reviewer rotation) r? `@ghost` `@rustbot` modify labels: rollup

…ross,bjorn3 Stabilize `repr128` ## Stabilisation report The `repr128` feature ([tracking issue](rust-lang#56071)) allows the use of `#[repr(u128)]` and `#[repr(i128)]` on enums in the same way that other primitive representations such as `#[repr(u64)]` can be used. For example: ```rust #[repr(u128)] enum Foo { One = 1, Two, Big = u128::MAX, } #[repr(i128)] enum Bar { HasThing(u16) = 42, HasSomethingElse(i64) = u64::MAX as i128 + 1, HasNothing, } ``` This is the final part of adding 128-bit integers to Rust ([RFC 1504](https://rust-lang.github.io/rfcs/1504-int128.html)); all other parts of 128-bit integer support were stabilised in rust-lang#49101 back in 2018. From a design perspective, `#[repr(u128)]`/`#[repr(i128)]` function like `#[repr(u64)]`/`#[repr(i64)]` but for 128-bit integers instead of 64-bit integers. The only differences are: - FFI safety: as `u128`/`i128` are not currently considered FFI safe, neither are `#[repr(u128)]`/`#[repr(i128)]` enums (I discovered this wasn't the case while drafting this stabilisation report, so I have submitted rust-lang#138282 to fix this). - Debug info: while none of the major debuggers currently support 128-bit integers, as of LLVM 20 `rustc` will emit valid debuginfo for both DWARF and PDB (PDB makes use of the same natvis that is also used for all enums with fields, whereas DWARF has native support). Tests for `#[repr(u128)]`/`#[repr(i128)]` enums include: - [ui/enum-discriminant/repr128.rs](https://github.com/rust-lang/rust/blob/385970f0c1fd0c09bac426b02f38300c0b1ba9a2/tests/ui/enum-discriminant/repr128.rs): checks that 128-bit enum discriminants have the correct values. - [debuginfo/msvc-pretty-enums.rs](https://github.com/rust-lang/rust/blob/385970f0c1fd0c09bac426b02f38300c0b1ba9a2/tests/debuginfo/msvc-pretty-enums.rs): checks the PDB debuginfo is correct. - [run-make/repr128-dwarf](https://github.com/rust-lang/rust/blob/385970f0c1fd0c09bac426b02f38300c0b1ba9a2/tests/run-make/repr128-dwarf/rmake.rs): checks the DWARF debuginfo is correct. Stabilising this feature does not require any changes to the Rust Reference as [the documentation on primitive representations](https://doc.rust-lang.org/nightly/reference/type-layout.html#r-layout.repr.primitive.intro) already includes `u128` and `i128`. Closes rust-lang#56071 Closes rust-lang/reference#1368 r? lang ```@rustbot``` label +I-lang-nominated +T-lang

Rollup of 4 pull requests Successful merges: - #138285 (Stabilize `repr128`) - #139994 (add `CStr::display`) - #141571 (coretests: extend and simplify float tests) - #141656 (CI: Add cargo tests to aarch64-apple-darwin) Failed merges: - #141430 (remove `visit_clobber` and move `DummyAstNode` to `rustc_expand`) - #141636 (avoid some usages of `&mut P<T>` in AST visitors) r? `@ghost` `@rustbot` modify labels: rollup

rustbot assigned traviscross Mar 9, 2025

rustbot added T-rustdoc-frontend Relevant to the rustdoc-frontend team, which will review and decide on the web UI/UX output. I-lang-nominated Nominated for discussion during a lang team meeting. labels Mar 9, 2025

beetrees mentioned this pull request Mar 9, 2025

Mark feature(repr128) as a complete feature #137592

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Tracking issue for feature(repr128); enums with 128-bit discriminants #56071

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aDotInTheVoid removed A-rustdoc-search Area: Rustdoc's search feature T-rustdoc-frontend Relevant to the rustdoc-frontend team, which will review and decide on the web UI/UX output. labels Mar 9, 2025

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rfcbot added proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. disposition-merge This issue / PR is in PFCP or FCP with a disposition to merge it. labels Mar 10, 2025

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Rollup of 11 pull requests #141688

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Stabilise repr128

467eeab

beetrees force-pushed the repr128-stable branch from 30f13ca to 467eeab Compare May 28, 2025 14:15

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Rollup of 7 pull requests #141707

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Rollup of 8 pull requests #141710

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Rollup of 4 pull requests #141717

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Stabilize `repr128` #138285

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