`ty::Alias` refactor by WaffleLapkin · Pull Request #154758 · rust-lang/rust

WaffleLapkin · 2026-04-03T14:51:11Z

This PR changes the following alias-related types from this:

pub enum AliasTyKind {
    Projection,
    Inherent,
    Opaque,
    Free,
}

pub struct AliasTy<I: Interner> {
    pub args: I::GenericArgs,
    pub def_id: I::DefId,
}

pub enum TyKind<I: Interner> {
    ...
    Alias(AliasTyKind, AliasTy<I>),
}

Into this:

pub enum AliasTyKind<I: Interner> {
    Projection { def_id: I::DefId },
    Inherent { def_id: I::DefId },
    Opaque { def_id: I::DefId },
    Free { def_id: I::DefId },
}

pub struct AliasTy<I: Interner> {
    pub args: I::GenericArgs,
    pub kind: AliasTyKind<I>,
}

pub enum TyKind<I: Interner> {
    ...
    Alias(AliasTy<I>),
}

... and then does a thousand other changes to accommodate for this change everywhere.

This brings us closer to being able to have AliasTyKinds which don't require a DefId (and thus can be more easily created, etc). Although notably we depend on both AliasTyKind -> DefId and DefId -> AliasTyKind conversions in a bunch of places still.

r? lcnr

A lot of these changes were done either by search & replace (via ast-grep) or on auto pilot, so I'm not quite sure I didn't mess up somewhere, but at least tests pass...

rustbot · 2026-04-03T14:51:19Z

Some changes occurred in exhaustiveness checking

cc @Nadrieril

Some changes occurred in need_type_info.rs

cc @lcnr

changes to the core type system

cc @lcnr

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

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

This PR changes rustc_public

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

HIR ty lowering was modified

cc @fmease

lcnr

winning!

Let's add a refactor tracking issue for future cleanups:

replace all the <name> @ ty::AliasTy { matches with just using args: <name>_args instead

I think similarly, the assert on AliasTy is less valuable now that we go through AliasTyKind, so maybe remove the assert, third field, and make matches nicer again

let's also look at def_id: did and do a rename to make that unnecessary in a future PR.

Ideally we don't have new_from_def_id or a alias_ty_kind_from_def_id but instead call e.g. new_projection directly, also future work

I also expect that most uses of AliasTyKind::def_id should be made unnecessary via a larger rewrite of the code

is_impl_trait should be renamed to is_opaque

there are uses of tcx.mk_ty_from_kind which should be a more specific constructor method

please rebase -> perf -> r=me if the impact is as expected from the size change test

View changes since this review

compiler/rustc_type_ir/src/outlives.rs

lcnr · 2026-04-06T08:06:31Z

compiler/rustc_type_ir/src/ty_kind.rs

+        /// During codegen, `interner.type_of(def_id)` can be used to get the type of the
+        /// underlying type if the type is an opaque.


that comment feels wrong here

should be on Opaque

also vibes: I prefer keeping comments on the variant if there's just a single field, otherwise the formatting is kinda /

I like it more on the variant, but changed anyway.

I think I fixed the docs, can you double check?

compiler/rustc_trait_selection/src/error_reporting/infer/mod.rs

compiler/rustc_type_ir/src/predicate.rs

compiler/rustc_type_ir/src/relate.rs

rustbot · 2026-04-06T13:06:50Z

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.

WaffleLapkin · 2026-04-06T13:08:38Z

@bors try @rust-timer queue

`ty::Alias` refactor

rust-bors · 2026-04-06T15:15:59Z

☀️ Try build successful (CI)
Build commit: 5340284 (5340284638d1148f25eaeb7e354eb90237024842, parent: 5a0d572cd1bbe1e3f75d64b32d86dbd277ce4b89)

rust-timer · 2026-04-06T15:56:07Z

Finished benchmarking commit (5340284): 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)	0.3%	[0.1%, 0.5%]	15
Improvements ✅ (primary)	-0.1%	[-0.1%, -0.1%]	1
Improvements ✅ (secondary)	-0.3%	[-0.3%, -0.2%]	4
All ❌✅ (primary)	-0.1%	[-0.1%, -0.1%]	1

Max RSS (memory usage)

Results (primary 1.6%, secondary 0.3%)

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

	mean	range	count
Regressions ❌ (primary)	1.6%	[0.5%, 4.4%]	5
Regressions ❌ (secondary)	1.2%	[1.0%, 2.0%]	5
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-4.3%	[-4.3%, -4.3%]	1
All ❌✅ (primary)	1.6%	[0.5%, 4.4%]	5

Cycles

Results (secondary -0.9%)

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)	2.4%	[1.8%, 3.0%]	4
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-7.6%	[-10.5%, -4.7%]	2
All ❌✅ (primary)	-	-	0

Binary size

Results (primary 0.0%, secondary 0.0%)

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

	mean	range	count
Regressions ❌ (primary)	0.0%	[0.0%, 0.0%]	4
Regressions ❌ (secondary)	0.0%	[0.0%, 0.0%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.0%	[0.0%, 0.0%]	4

Bootstrap: 488.486s -> 488.964s (0.10%)
Artifact size: 395.12 MiB -> 395.18 MiB (0.01%)

lcnr

r=me after removing the new_from_args file

View changes since this review

lcnr · 2026-04-07T08:07:56Z

@bors rollup=never

Add `#[track_caller]` to some functions which can panic b/c of the caller's wrong index (this helped me debug some mistakes I did while refactoring `ty::Alias`)

WaffleLapkin · 2026-04-07T12:18:15Z

@bors r=lcnr

rust-bors · 2026-04-07T12:18:19Z

📌 Commit 6ab50d5 has been approved by lcnr

It is now in the queue for this repository.

rust-bors · 2026-04-07T16:32:00Z

☀️ Test successful - CI
Approved by: lcnr
Duration: 3h 34m 55s
Pushing c3bd628 to main...

github-actions · 2026-04-07T16:35:15Z

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 49b6ac0 (parent) -> c3bd628 (this PR)

Test differences

Show 98 test diffs

98 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 c3bd6289f65fa7210c50bdeeb0ed4541caa33d2d --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: 1h 34m -> 1h 54m (+21.5%)
dist-x86_64-apple: 2h 10m -> 1h 47m (-17.2%)
aarch64-apple: 3h -> 3h 28m (+15.9%)
dist-aarch64-msvc: 1h 34m -> 1h 46m (+12.7%)
dist-aarch64-apple: 1h 52m -> 2h 4m (+10.7%)
pr-check-2: 41m 15s -> 44m 42s (+8.4%)
x86_64-msvc-ext1: 2h 5m -> 2h 15m (+8.2%)
dist-x86_64-netbsd: 1h 27m -> 1h 20m (-7.9%)
x86_64-msvc-ext2: 1h 57m -> 1h 48m (-7.9%)
dist-aarch64-llvm-mingw: 1h 32m -> 1h 39m (+7.7%)

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 · 2026-04-07T17:12:36Z

Finished benchmarking commit (c3bd628): 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)	0.3%	[0.1%, 0.5%]	14
Improvements ✅ (primary)	-0.2%	[-0.2%, -0.1%]	2
Improvements ✅ (secondary)	-0.2%	[-0.3%, -0.2%]	5
All ❌✅ (primary)	-0.2%	[-0.2%, -0.1%]	2

Max RSS (memory usage)

Results (primary 1.0%, secondary 1.3%)

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

	mean	range	count
Regressions ❌ (primary)	1.0%	[0.9%, 1.1%]	2
Regressions ❌ (secondary)	2.4%	[0.9%, 4.2%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.1%	[-2.1%, -2.1%]	1
All ❌✅ (primary)	1.0%	[0.9%, 1.1%]	2

Cycles

Results (secondary 1.4%)

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)	6.4%	[6.4%, 6.4%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.6%	[-3.6%, -3.6%]	1
All ❌✅ (primary)	-	-	0

Binary size

Results (primary 0.1%, secondary 0.1%)

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

	mean	range	count
Regressions ❌ (primary)	0.1%	[0.0%, 0.1%]	63
Regressions ❌ (secondary)	0.1%	[0.0%, 0.1%]	24
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.1%	[0.0%, 0.1%]	63

Bootstrap: 487.434s -> 487.084s (-0.07%)
Artifact size: 395.10 MiB -> 395.18 MiB (0.02%)

rustbot assigned lcnr Apr 3, 2026

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WaffleLapkin force-pushed the aliassss branch from 56f6f98 to db98829 Compare April 3, 2026 16:51

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lcnr reviewed Apr 6, 2026

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ty::Alias refactor: change APIs

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WaffleLapkin force-pushed the aliassss branch from db98829 to af29e57 Compare April 6, 2026 13:06

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rust-bors bot pushed a commit that referenced this pull request Apr 6, 2026

Auto merge of #154758 - WaffleLapkin:aliassss, r=<try>

5340284

`ty::Alias` refactor

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Apr 6, 2026

WaffleLapkin force-pushed the aliassss branch from af29e57 to 0b33626 Compare April 6, 2026 13:10

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rustbot added perf-regression Performance regression. and removed S-waiting-on-perf Status: Waiting on a perf run to be completed. labels Apr 6, 2026

lcnr reviewed Apr 7, 2026

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WaffleLapkin added 3 commits April 7, 2026 10:08

ty::Alias refactor: fixup all the compiler code

0f76708

ty::Alias refactor: fix rustdoc

5d5cdef

ty::Alias refactor: fix clippy

2ea74a9

WaffleLapkin added 3 commits April 7, 2026 10:08

track caller

8c490f3

Add `#[track_caller]` to some functions which can panic b/c of the caller's wrong index (this helped me debug some mistakes I did while refactoring `ty::Alias`)

ty::Alias refactor: bless tests

ec8c489

ty::Alias review comments

6ab50d5

WaffleLapkin force-pushed the aliassss branch from 0b33626 to 6ab50d5 Compare April 7, 2026 08:09

WaffleLapkin mentioned this pull request Apr 7, 2026

tracking issue for ty::Alias refactor #154941

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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 Apr 7, 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 Apr 7, 2026

rust-bors bot merged commit c3bd628 into rust-lang:main Apr 7, 2026
12 checks passed

rustbot added this to the 1.96.0 milestone Apr 7, 2026

		/// During codegen, `interner.type_of(def_id)` can be used to get the type of the
		/// underlying type if the type is an opaque.

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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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