refactor(mgca): Change `DefKind::Const` and `DefKind::AssocConst` to have a `is_type_const` flag by JayanAXHF · Pull Request #153050 · rust-lang/rust

JayanAXHF · 2026-02-24T14:42:53Z

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Addresses #152940

Changed DefKind::Const and DefKind::AssocConst to have a is_type_const flag.
changed is_type_const query to check for this flag
removed is_rhs_type_const query

r? @BoxyUwU

rustbot · 2026-02-24T14:42:57Z

Some changes occurred to the CTFE machinery

cc @RalfJung, @oli-obk, @lcnr

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

changes to the core type system

cc @lcnr

Some changes occurred in match checking

cc @Nadrieril

HIR ty lowering was modified

cc @fmease

This PR changes rustc_public

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

rustbot · 2026-02-24T18:11:53Z

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

JayanAXHF · 2026-02-24T23:00:48Z

@BoxyUwU I think this is mostly complete now

BoxyUwU

Thanks for looking into this :3 it looks correct, just a few minor comments

View changes since this review

BoxyUwU · 2026-02-25T10:50:09Z

compiler/rustc_middle/src/ty/assoc.rs

    pub fn as_def_kind(&self) -> DefKind {
        match self {
-            Self::Const { .. } => DefKind::AssocConst,
+            Self::Const { .. } => DefKind::AssocConst { is_type_const: false },


unconditionally using false for is_type_const seems wrong. AssocKind::Const might need to be extended to also track is_type_const

Hmm yeah, that seems fair

compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

compiler/rustc_middle/src/ty/context.rs

fmease · 2026-02-25T13:36:20Z

Since this change was largely motivated by a perf regression:

@bors try @rust-timer queue

refactor(mgca): Change `DefKind::Const` and `DefKind::AssocConst` to have a `is_type_const` flag

BoxyUwU · 2026-02-25T13:53:08Z

Oh an additional thing we can do is remove the IsTypeConst flag from hir::TraitItemKind, that information should now be available via the DefKind's flag. That might also help with perf a bit (unsure)

rust-bors · 2026-02-25T15:52:19Z

☀️ Try build successful (CI)
Build commit: c01784d (c01784d8d0858fd818d2ea1182e0864c10601aec, parent: 3f9853562c73af38a5e6af8b0da1b2734a327e19)

JayanAXHF · 2026-02-25T18:44:58Z

Oh an additional thing we can do is remove the IsTypeConst flag from hir::TraitItemKind, that information should now be available via the DefKind's flag. That might also help with perf a bit (unsure)

I'd suggest having that in a different PR after this one lands (stacked PRs ftw). This is already a pretty widespread refactor, and IMO having that in a separate PR would be easier to work with

rust-timer · 2026-02-25T19:25:57Z

Finished benchmarking commit (c01784d): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.7%	[0.0%, 1.3%]	2
Improvements ✅ (primary)	-0.5%	[-0.8%, -0.2%]	17
Improvements ✅ (secondary)	-0.7%	[-1.7%, -0.2%]	10
All ❌✅ (primary)	-0.5%	[-0.8%, -0.2%]	17

Max RSS (memory usage)

Results (primary -1.4%, secondary 0.5%)

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)	-1.4%	[-2.2%, -0.6%]	2
Improvements ✅ (secondary)	-1.1%	[-1.1%, -1.1%]	1
All ❌✅ (primary)	-1.4%	[-2.2%, -0.6%]	2

Cycles

Results (primary -2.5%, secondary 7.7%)

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)	7.7%	[7.7%, 7.7%]	1
Improvements ✅ (primary)	-2.5%	[-2.5%, -2.5%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.5%	[-2.5%, -2.5%]	1

Binary size

Results (primary -0.5%, secondary -0.7%)

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

	mean	range	count
Regressions ❌ (primary)	0.2%	[0.1%, 0.2%]	4
Regressions ❌ (secondary)	0.1%	[0.1%, 0.1%]	1
Improvements ✅ (primary)	-0.6%	[-1.2%, -0.0%]	60
Improvements ✅ (secondary)	-0.7%	[-1.6%, -0.0%]	23
All ❌✅ (primary)	-0.5%	[-1.2%, 0.2%]	64

Bootstrap: 480.701s -> 486.306s (1.17%)
Artifact size: 397.77 MiB -> 397.77 MiB (0.00%)

compiler/rustc_middle/src/ty/context.rs

JonathanBrouwer · 2026-02-28T16:43:26Z

@bors p=6
Scheduling this before the next rollup

JayanAXHF · 2026-02-28T16:49:21Z

@BoxyUwU shouldn't we squash the commits (there's a lot of "ci appeasing" commits here)

BoxyUwU · 2026-02-28T17:27:32Z

oh uhh yeah that's probably a good idea hmm

BoxyUwU · 2026-02-28T17:27:37Z

@bors r-

BoxyUwU · 2026-02-28T17:27:42Z

@bors squash

rust-bors · 2026-02-28T17:27:45Z

🚧 Squashing... this can take a few minutes.

…have a `is_type_const` flag * refactor: add `is_type_const` flag to `DefKind::Const` and `AssocConst` * refactor(cleanup) remove the `rhs_is_type_const` query * style: fix formatting * refactor: refactor stuff in librustdoc for new Const and AssocConst * refactor: refactor clippy for the changes * chore: formatting * fix: fix test * fix: fix suggestions * Update context.rs Co-authored-by: Boxy <rust@boxyuwu.dev> * changed AssocKind::Const to store data about being a type const

rust-bors · 2026-02-28T17:28:02Z

🔨 10 commits were squashed into efc150e.

BoxyUwU · 2026-02-28T17:28:28Z

@bors r+

rust-bors · 2026-02-28T17:28:30Z

📌 Commit efc150e has been approved by BoxyUwU

It is now in the queue for this repository.

rust-bors · 2026-02-28T21:57:45Z

☀️ Test successful - CI
Approved by: BoxyUwU
Duration: 3h 30m 33s
Pushing 38c0de8 to main...

github-actions · 2026-02-28T22:00:32Z

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 ba15679 (parent) -> 38c0de8 (this PR)

Test differences

Show 86 test diffs

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

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard 38c0de8dcb14d42290042521be9958d37f3fa390 --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-apple-various: 2h 4m -> 1h 40m (-19.4%)
aarch64-apple: 2h 51m -> 3h 23m (+18.5%)
dist-aarch64-apple: 1h 59m -> 1h 44m (-12.5%)
dist-x86_64-apple: 2h 9m -> 1h 54m (-11.7%)
x86_64-gnu-miri: 1h 20m -> 1h 28m (+10.0%)
armhf-gnu: 1h 31m -> 1h 22m (-9.9%)
dist-aarch64-llvm-mingw: 1h 30m -> 1h 38m (+9.6%)
x86_64-msvc-ext2: 1h 47m -> 1h 57m (+9.1%)
dist-armv7-linux: 1h 35m -> 1h 27m (-8.4%)
aarch64-msvc-2: 1h 44m -> 1h 52m (+7.9%)

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 · 2026-02-28T22:38:47Z

Finished benchmarking commit (38c0de8): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

Our benchmarks found a performance regression caused by this PR.
This might be an actual regression, but it can also be just noise.

Next Steps:

If the regression was expected or you think it can be justified,
please write a comment with sufficient written justification, and add
@rustbot label: +perf-regression-triaged to it, to mark the regression as triaged.
If you think that you know of a way to resolve the regression, try to create
a new PR with a fix for the regression.
If you do not understand the regression or you think that it is just noise,
you can ask the @rust-lang/wg-compiler-performance working group for help (members of this group
were already notified of this PR).

@rustbot label: +perf-regression
cc @rust-lang/wg-compiler-performance

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.0%	[0.0%, 0.0%]	1
Improvements ✅ (primary)	-0.5%	[-0.8%, -0.2%]	17
Improvements ✅ (secondary)	-0.7%	[-1.7%, -0.0%]	10
All ❌✅ (primary)	-0.5%	[-0.8%, -0.2%]	17

Max RSS (memory usage)

Results (primary -2.3%, secondary 1.7%)

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)	1.7%	[0.9%, 3.2%]	7
Improvements ✅ (primary)	-2.3%	[-2.3%, -2.3%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.3%	[-2.3%, -2.3%]	1

Cycles

Results (secondary -3.8%)

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)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.8%	[-3.8%, -3.8%]	1
All ❌✅ (primary)	-	-	0

Binary size

Results (primary -0.5%, secondary -0.5%)

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

	mean	range	count
Regressions ❌ (primary)	0.2%	[0.1%, 0.2%]	4
Regressions ❌ (secondary)	0.1%	[0.1%, 0.1%]	1
Improvements ✅ (primary)	-0.5%	[-1.2%, -0.0%]	67
Improvements ✅ (secondary)	-0.5%	[-1.6%, -0.0%]	32
All ❌✅ (primary)	-0.5%	[-1.2%, 0.2%]	71

Bootstrap: 479.975s -> 481.431s (0.30%)
Artifact size: 395.63 MiB -> 397.60 MiB (0.50%)

panstromek · 2026-03-02T16:07:15Z

perf triage:

Tiny regression in include-blob stress test, overall positive.

@rustbot label: +perf-regression-triaged

@BoxyUwU

…nst, r=BoxyUwU refactor(mgca): Change `DefKind::Const` and `DefKind::AssocConst` to have a `is_type_const` flag Addresses rust-lang#152940 - Changed `DefKind::Const` and `DefKind::AssocConst` to have a `is_type_const` flag. - changed `is_type_const` query to check for this flag - removed `is_rhs_type_const` query r? @BoxyUwU

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rust-bors bot pushed a commit that referenced this pull request Feb 25, 2026

Auto merge of #153050 - JayanAXHF:refactor/change-is-type-const, r=<try>

c01784d

refactor(mgca): Change `DefKind::Const` and `DefKind::AssocConst` to have a `is_type_const` flag

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BoxyUwU mentioned this pull request Feb 28, 2026

Tracking Issue for Generic Constant Arguments MVP #132980

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rust-bors bot merged commit 38c0de8 into rust-lang:main Feb 28, 2026
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Lint unused associated types #148654

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JayanAXHF mentioned this pull request Mar 5, 2026

mGCA: Track whether a const is a type const as part of DefKind #152940

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BoxyUwU mentioned this pull request Mar 16, 2026

Don't look for non-type-level assoc consts when checking trait object types #153738

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Overall result: ❌✅ regressions and improvements - please read the text below

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Test differences

Job duration changes

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Overall result: ❌✅ regressions and improvements - please read the text below

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