yeet type const

[khyperia]

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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]

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]

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

[rustbot]

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

[BoxyUwU]

@bors r+ rollup=never

[rust-bors]

📌 Commit f5eb9e4 has been approved by BoxyUwU

It is now in the queue for this repository.

[BoxyUwU]

@bors p=1

[rust-log-analyzer]

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]

💔 Test for e36ddcd failed: CI. Failed job:

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

[JonathanBrouwer]

@bors retry

[rust-bors]

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

[github-actions]

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

• J0: test-aarch64-apple-1, test-aarch64-apple-macos-26-1, test-aarch64-gnu, test-aarch64-gnu-llvm-21-1, test-aarch64-msvc-1, test-arm-android, test-armhf-gnu, test-i686-gnu-1, test-i686-gnu-nopt-1, test-i686-msvc, test-various, test-x86_64-gnu, test-x86_64-gnu-debug, test-x86_64-gnu-gcc, test-x86_64-gnu-llvm-21, test-x86_64-gnu-llvm-21-2, test-x86_64-gnu-llvm-22-2, test-x86_64-gnu-nopt, test-x86_64-gnu-parallel-frontend, test-x86_64-gnu-stable, test-x86_64-mingw-1, test-x86_64-msvc-1
• J1: test-x86_64-gnu-next-trait-solver-polonius
• J2: test-x86_64-gnu-llvm-21-3, test-x86_64-gnu-llvm-22-3, test-x86_64-gnu-next-trait-solver-polonius

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

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

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%)