yeet `type const` by khyperia · Pull Request #162517 · rust-lang/rust

khyperia · 2026-09-09T08:40:40Z

tracking issue: #132980

zulip thread context (design decussion of future of gca): #project-const-generics > talkies at last @ 💬

this PR does two things:

implement #[rustc_always_gca] (bikeshed name thread: #project-const-generics > #[always_gca] bikeshed )
remove type const syntax

it also migrates the test suite to the syntax introduced in #162179 i.e. the new way to write type const is now const ITEM: T = core::direct_const_arg!(V); (ouch my hands, that took a while)

r? @BoxyUwU

rustbot · 2026-09-09T08:40:44Z

This PR changes rustc_public

cc @oli-obk, @celinval, @ouz-a, @makai410

Some changes occurred in match checking

cc @Nadrieril

The parser was modified, potentially altering the grammar of (stable) Rust
which would be a breaking change.

cc @fmease

HIR ty lowering was modified

cc @fmease

Some changes occurred in compiler/rustc_attr_ir

cc @jdonszelmann, @JonathanBrouwer

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

rustfmt is developed in its own repository. If possible, consider making this change to rust-lang/rustfmt instead.

cc @rust-lang/rustfmt

clippy is developed in its own repository. If possible, consider making this change to rust-lang/rust-clippy instead.

cc @rust-lang/clippy

Some changes occurred in compiler/rustc_passes/src/check_attr.rs

cc @jdonszelmann, @JonathanBrouwer

Some changes occurred to the CTFE machinery

cc @RalfJung, @oli-obk, @lcnr

Some changes occurred in compiler/rustc_attr_parsing

cc @jdonszelmann, @JonathanBrouwer

This PR changes a file inside tests/crashes. If a crash was fixed, please move into the corresponding ui subdir and add 'Fixes #' to the PR description to autoclose the issue upon merge.

rustbot · 2026-09-09T08:40:46Z

BoxyUwU is currently at their maximum review capacity.
They may take a while to respond.

rustbot · 2026-09-11T14:01:29Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

BoxyUwU

r=me once CI is green

@bors rollup=never p=1

View changes since this review

rust-log-analyzer · 2026-09-12T04:04:58Z

The job test-i686-msvc failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

rust-bors · 2026-09-12T04:10:06Z

💔 Test for e36ddcd failed: CI. Failed job:

auto - test-i686-msvc (web logs, enhanced plaintext logs)

JonathanBrouwer · 2026-09-12T06:29:40Z

@bors retry

rust-bors · 2026-09-12T10:24:40Z

☀️ Test successful - CI
Approved by: BoxyUwU
Duration: 3h 6m 5s
Pushing 9c99d05 to main...

github-actions · 2026-09-12T10:27:36Z

What is this?

This is an experimental post-merge analysis report that shows differences in test outcomes between the merged PR and its parent PR.

Comparing 74b3f08 (parent) -> 9c99d05 (this PR)

Test differences

Show 111 test diffs

Stage 1

[ui (polonius)] tests/ui/const-generics/mgca/free-const-recursive.rs: pass -> [missing] (J1)
[ui (polonius)] tests/ui/const-generics/mgca/free-const-recursive.rs#gca: [missing] -> pass (J1)
[ui (polonius)] tests/ui/const-generics/mgca/free-const-recursive.rs#min_gca: [missing] -> pass (J1)
[ui (polonius)] tests/ui/const-generics/mgca/suggest-direct-const.rs: [missing] -> pass (J1)
[ui (polonius)] tests/ui/const-generics/mgca/suggest-pub-type_const.rs: pass -> [missing] (J1)
[ui] tests/ui/const-generics/mgca/free-const-recursive.rs: pass -> [missing] (J2)
[ui] tests/ui/const-generics/mgca/free-const-recursive.rs#gca: [missing] -> pass (J2)
[ui] tests/ui/const-generics/mgca/free-const-recursive.rs#min_gca: [missing] -> pass (J2)
[ui] tests/ui/const-generics/mgca/suggest-direct-const.rs: [missing] -> pass (J2)
[ui] tests/ui/const-generics/mgca/suggest-pub-type_const.rs: pass -> [missing] (J2)

Stage 2

[ui] tests/ui/const-generics/mgca/free-const-recursive.rs: pass -> [missing] (J0)
[ui] tests/ui/const-generics/mgca/free-const-recursive.rs#gca: [missing] -> pass (J0)
[ui] tests/ui/const-generics/mgca/free-const-recursive.rs#min_gca: [missing] -> pass (J0)
[ui] tests/ui/const-generics/mgca/suggest-direct-const.rs: [missing] -> pass (J0)
[ui] tests/ui/const-generics/mgca/suggest-pub-type_const.rs: pass -> [missing] (J0)

Additionally, 96 doctest diffs were found. These are ignored, as they are noisy.

Job group index

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard 9c99d05505bccb67912d68e05fe7fc7c58afcb41 --output-dir test-dashboard

And then open test-dashboard/index.html in your browser to see an overview of all executed tests.

Job duration changes

dist-armv7-linux: 1h 8m -> 1h 39m (+45.9%)
test-i686-gnu-1: 2h 14m -> 1h 16m (-42.9%)
test-x86_64-gnu-stdlib-semver-check: 17m 15s -> 9m 57s (-42.3%)
test-x86_64-msvc-ext2: 1h 13m -> 1h 40m (+37.2%)
test-x86_64-gnu-tools: 1h 10m -> 48m 38s (-31.2%)
dist-x86_64-illumos: 1h 47m -> 1h 14m (-30.7%)
test-x86_64-gnu-stable: 2h 39m -> 1h 50m (-30.4%)
test-i686-gnu-nopt-2: 1h 47m -> 2h 20m (+30.3%)
dist-x86_64-netbsd: 1h 14m -> 1h 36m (+29.7%)
optional-test-x86_64-gnu-autodiff: 55m 8s -> 39m 23s (-28.6%)

How to interpret the job duration changes?

Job durations can vary a lot, based on the actual runner instance
that executed the job, system noise, invalidated caches, etc. The table above is provided
mostly for t-infra members, for simpler debugging of potential CI slow-downs.

rust-timer · 2026-09-12T11:09:56Z

Finished benchmarking commit (9c99d05): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

This perf run didn't have relevant results for this metric.

Max RSS (memory usage)

Results (primary -1.1%, secondary -2.2%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.1%	[2.1%, 2.1%]	1
Improvements ✅ (primary)	-1.1%	[-2.1%, -0.4%]	9
Improvements ✅ (secondary)	-2.9%	[-4.5%, -1.1%]	6
All ❌✅ (primary)	-1.1%	[-2.1%, -0.4%]	9

Cycles

Results (primary 0.5%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	1.0%	[0.4%, 3.1%]	8
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.6%	[-0.9%, -0.4%]	4
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.5%	[-0.9%, 3.1%]	12

Binary size

This perf run didn't have relevant results for this metric.

Bootstrap: 493.042s -> 497.802s (0.97%)
Artifact size: 406.92 MiB -> 406.93 MiB (0.00%)

@BoxyUwU

…yUwU reintroduce check RibKind::ConstParamTy did in direct consts The ConstParamTy nameres rib checks were never implemented for `gca!`-rhs direct consts. So, when `type const` got removed in rust-lang#162517 and we now only have `gca!`-rhs direct consts, the lack of checks became very apparent This PR adds the check again for `gca!`-rhs direct consts. When implementing this and updating `tests/ui/const-generics/mgca/type_const-generic-param-in-type.rs`, I ran into rust-lang#160553 which caused a glaringly obvious issue - the following succeeds compilation: ```rust #![feature(min_generic_const_args, generic_const_items, generic_const_parameter_types)] const BAR<const N: usize>: [(); N] = core::direct_const_arg!([]); ``` This is already tracked in `tests/crashes/160553.rs` so I have not added a test for it. This is the reason I changed the test from `[(); N]` to `StructWithConstParam<const N: usize>`, the RHS has to, like, y'know, actually typecheck :P r? @BoxyUwU

@BoxyUwU

…yUwU reintroduce check RibKind::ConstParamTy did in direct consts The ConstParamTy nameres rib checks were never implemented for `gca!`-rhs direct consts. So, when `type const` got removed in rust-lang#162517 and we now only have `gca!`-rhs direct consts, the lack of checks became very apparent This PR adds the check again for `gca!`-rhs direct consts. When implementing this and updating `tests/ui/const-generics/mgca/type_const-generic-param-in-type.rs`, I ran into rust-lang#160553 which caused a glaringly obvious issue - the following succeeds compilation: ```rust #![feature(min_generic_const_args, generic_const_items, generic_const_parameter_types)] const BAR<const N: usize>: [(); N] = core::direct_const_arg!([]); ``` This is already tracked in `tests/crashes/160553.rs` so I have not added a test for it. This is the reason I changed the test from `[(); N]` to `StructWithConstParam<const N: usize>`, the RHS has to, like, y'know, actually typecheck :P r? @BoxyUwU

@BoxyUwU

…yUwU reintroduce check RibKind::ConstParamTy did in direct consts The ConstParamTy nameres rib checks were never implemented for `gca!`-rhs direct consts. So, when `type const` got removed in rust-lang#162517 and we now only have `gca!`-rhs direct consts, the lack of checks became very apparent This PR adds the check again for `gca!`-rhs direct consts. When implementing this and updating `tests/ui/const-generics/mgca/type_const-generic-param-in-type.rs`, I ran into rust-lang#160553 which caused a glaringly obvious issue - the following succeeds compilation: ```rust #![feature(min_generic_const_args, generic_const_items, generic_const_parameter_types)] const BAR<const N: usize>: [(); N] = core::direct_const_arg!([]); ``` This is already tracked in `tests/crashes/160553.rs` so I have not added a test for it. This is the reason I changed the test from `[(); N]` to `StructWithConstParam<const N: usize>`, the RHS has to, like, y'know, actually typecheck :P r? @BoxyUwU

@BoxyUwU

Rollup merge of #162842 - khyperia:ConstParamTy-check, r=BoxyUwU reintroduce check RibKind::ConstParamTy did in direct consts The ConstParamTy nameres rib checks were never implemented for `gca!`-rhs direct consts. So, when `type const` got removed in #162517 and we now only have `gca!`-rhs direct consts, the lack of checks became very apparent This PR adds the check again for `gca!`-rhs direct consts. When implementing this and updating `tests/ui/const-generics/mgca/type_const-generic-param-in-type.rs`, I ran into #160553 which caused a glaringly obvious issue - the following succeeds compilation: ```rust #![feature(min_generic_const_args, generic_const_items, generic_const_parameter_types)] const BAR<const N: usize>: [(); N] = core::direct_const_arg!([]); ``` This is already tracked in `tests/crashes/160553.rs` so I have not added a test for it. This is the reason I changed the test from `[(); N]` to `StructWithConstParam<const N: usize>`, the RHS has to, like, y'know, actually typecheck :P r? @BoxyUwU

rustbot assigned BoxyUwU Sep 9, 2026

fmease mentioned this pull request Sep 9, 2026

Remove type const items fmease/rasur#39

Merged

JonathanBrouwer reviewed Sep 9, 2026

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Comment thread compiler/rustc_attr_parsing/src/attributes/semantics.rs Outdated

JonathanBrouwer reviewed Sep 9, 2026

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Comment thread compiler/rustc_ast_passes/src/feature_gate.rs

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khyperia force-pushed the yeet-type-const branch from e6a7e81 to e0f1715 Compare September 9, 2026 10:21

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khyperia force-pushed the yeet-type-const branch from e0f1715 to bdab9e9 Compare September 9, 2026 13:37

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khyperia force-pushed the yeet-type-const branch from bdab9e9 to b6041c5 Compare September 11, 2026 12:55

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khyperia force-pushed the yeet-type-const branch from b6041c5 to a6afda2 Compare September 11, 2026 14:01

BoxyUwU approved these changes Sep 11, 2026

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khyperia mentioned this pull request Sep 11, 2026

[Work Item]: ConstParamTy checks for type of direct const items is unchecked/unimplemented rust-lang/project-const-generics#120

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khyperia added 4 commits September 11, 2026 17:08

implement #[rustc_always_gca]

5c5de6e

migrate tests

0c35264

yeet type const

e93270b

yeet braces from DefKind::Const

06e076e

rust-bors Bot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Sep 12, 2026

rust-bors Bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Sep 12, 2026

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rust-bors Bot added merged-by-bors This PR was explicitly merged by bors. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Sep 12, 2026

rust-bors Bot merged commit 9c99d05 into rust-lang:main Sep 12, 2026
15 checks passed

rustbot added this to the 1.100.0 milestone Sep 12, 2026

khyperia deleted the yeet-type-const branch September 12, 2026 10:28

dtolnay mentioned this pull request Sep 13, 2026

Parse type const syntax dtolnay/syn#1984

Closed

This was referenced Sep 14, 2026

[ICE]: can't type-check body of DefId mgca + supertrait_item_shadowing (none-gce repro) #159169

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ICE: unelided lifetime in signature #142773

Closed

khyperia mentioned this pull request Sep 16, 2026

reintroduce check RibKind::ConstParamTy did in direct consts #162842

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Test differences

Stage 1

Stage 2

Job duration changes

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Overall result: no relevant changes - no action needed

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