implement `Move` trait prototype by nia-e · Pull Request #156018 · rust-lang/rust

nia-e · 2026-04-30T21:32:00Z

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Add a barebones implementation for Move (#149607), pending some diagnostics changes & tests.

TODO

next solver currently errors when not enabling feature(move_trait)
change printing of trait objects to not show Move
change printing of opaque types to not show Move

r? lcnr

nia-e · 2026-04-30T21:33:46Z

@bors try @rust-timer queue

implement `Move` trait prototype

nia-e · 2026-04-30T21:34:49Z

(tests are broken, mostly due to diagnostics changing)

lcnr · 2026-05-01T07:27:04Z

the zerovec changes rely on a need candidate preference change 🤔 :3

what i've done in https://github.com/rust-lang/rust/pull/146201/changes#diff-34d5893dd95fe09f9a0fd3341efacd1c21853bb34ba29d9d79bb9af26bb8a0a0

lcnr · 2026-05-01T07:36:07Z

+        let key = self.infcx.param_env.and(type_op::prove_predicate::ProvePredicate { predicate });
+        let op = CustomTypeOp::new(
+            |ocx| {
+                let res = type_op::QueryTypeOp::perform_locally_with_next_solver(ocx, key, span);


if you look at what perform_locally_with_next_solver, it should just be the thing you do in the error path anyways 🤔 🤷

actually, we could make scrape_region_constraints generic over the expected errors, and have a FallibleCustomTypeOp which uses it while expecting potential errors. Instead instead of always emitting a delayed bug if there are errors, scrape_region_constraints would just report the failures as proper type errors 🤔 that seems nicer to me

View changes since the review

right, ok - wasn't sure if that level of overhaul was on the table. it was kind of difficult to recreate the predicate in scrape_region_constraints (thus me doing it this way) but if i can mess with it that makes my life easier :D

lcnr · 2026-05-01T07:44:10Z

+        let relaxed_bounds = collect_relaxed_bounds(hir_bounds, context);
+        self.reject_duplicate_relaxed_bounds(relaxed_bounds);
+
+        let Some(move_did) = tcx.lang_items().move_trait() else {


I'd just always require_lang_item :3 requiring core to provide the trait definition for Move seems innocent enough

View changes since the review

that's what I tried initially, but it means we need to add Move in a quadrillion tests that don't depend on core 🫠

we should have some mini_core somewhere that most such tests should use 😅

are there still proper #[no_core] tests that don't use an existing mini_core?

lcnr · 2026-05-01T07:51:09Z

        }

+        // Don't use `add_implicit_bounds` directly to skip adding `Sized`.
+        self.add_implicit_move_bound(


hmm, I'd prefer add_implicit_bound here, because otherwise we have to do that when adding Forget later on

View changes since the review

lcnr · 2026-05-01T07:52:16Z

    }

+    pub fn is_implicit_trait(self, def_id: DefId) -> bool {
+        self.is_default_trait(def_id) || matches!(self.as_lang_item(def_id), Some(LangItem::Move))


why are we not treating Sized as an implicit trait?

View changes since the review

Sized is weird enough (sometimes the bound is Sized, sometimes MetaSized etc) that i thought it made more sense to treat it separately. like, arguably MetaSized should also be an implicit trait but that would change behaviour at most callsites i think.

though i realise this is kinda confusing naming given that I also wrote add_implicit_trait_bounds that does add sized...

lcnr · 2026-05-01T07:53:10Z

            }

-            // Backward compatibility for default auto traits.
+            // Backward compatibility for default auto traits & `Move`.


this is somewhat meh, Move is a default auto trait 😅 ✨ , just not add default_auto_trait

View changes since the review

In general, this PR doesn't seem to use the "infrastructure" provided by internal feature more_maybe_bounds unlike earlier experiments.

I lack the context, so I don't know why that's done this way. However, if the "proper" Move and Forget default auto traits won't use all the preexisting MMB lowering routines, then I'd rather remove that internal feature entirely since it's evidently being supplanted (and also won't be needed anymore anyway as its purpose was to experiment with new default bounds).

Maintaining two incredibly similar but still somehow distinct features (default vs. "implicit") is somewhat meh I dare say. We probably want to notify Vadim then who is the owner of MMB IIRC.

yeah, I agree. Ripping out that feature in favor of actually having individual traits seems good to me. Reusing these features doesn't simplify adding new traits. Having one non-sized trait is nice to properly handle things though

nia-e · 2026-05-04T08:39:12Z

curious what the perf hit is without doing any special handling. should actually work this time :D

@bors try @rust-timer queue

lcnr · 2026-07-24T11:39:39Z

@bors try @rust-timer queue

implement `Move` trait prototype

rust-bors · 2026-07-24T12:25:21Z

💔 Test for b373540 failed: CI. Failed job:

try - dist-x86_64-linux-quick (web logs, enhanced plaintext logs)

it should give some info tho...

lcnr · 2026-08-21T10:23:33Z

@bors try @rust-timer queue

implement `Move` trait prototype

rust-log-analyzer · 2026-08-21T10:40:47Z

The job x86_64-gnu-gcc-core-tests failed! Check out the build log: (web) (plain enhanced) (plain)

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

---- mem::type_info::test_dynamic_traits stdout ----
---- mem::type_info::test_dynamic_traits stderr ----

thread 'main' (19749) panicked at library/coretests/tests/mem/type_info.rs:369:9:
assertion `left == right` failed: unexpected ids.
actual: [TypeId(0xeff143cada5c252eeb97a379bd3afff1), TypeId(0xb0ecf8e2d74c22b56d21dade0483b5c3)]
expected: [TypeId(0x58664381986b010a958eaa22c03eab81)]
  left: {TypeId(0xeff143cada5c252eeb97a379bd3afff1), TypeId(0xb0ecf8e2d74c22b56d21dade0483b5c3)}
 right: {TypeId(0x58664381986b010a958eaa22c03eab81)}
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
---- mem::type_info::test_dynamic_traits stdout end ----

failures:
    mem::type_info::test_dynamic_traits

Important

For more information how to resolve CI failures of this job, visit this link.

rust-bors · 2026-08-21T11:23:24Z

☀️ Try build successful (CI)
Build commit: a238f16 (a238f167ac6e36167ceb7d6094bd56262913350c)
Base parent: 16a623a (16a623ad672a92409b5c04beb303583c6cf72a7e)

rust-timer · 2026-08-21T12:41:43Z

Finished benchmarking commit (a238f16): comparison URL.

Overall result: ❌✅ regressions and improvements - please read:

Benchmarking means the PR may be perf-sensitive. It's automatically marked not fit for rolling up. Overriding is possible but disadvised: it risks changing compiler perf.

Next, please: If you can, justify the regressions found in this try perf run in writing along with @rustbot label: +perf-regression-triaged. If not, fix the regressions and do another perf run. Neutral or positive results will clear the label automatically.

@bors rollup=never rustc-perf
@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)	1.5%	[0.2%, 12.0%]	151
Regressions ❌ (secondary)	1.1%	[0.0%, 4.5%]	195
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.3%	[-0.4%, -0.2%]	3
All ❌✅ (primary)	1.5%	[0.2%, 12.0%]	151

Max RSS (memory usage)

Results (primary 1.7%, secondary 3.3%)

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

	mean	range	count
Regressions ❌ (primary)	1.9%	[0.4%, 5.9%]	23
Regressions ❌ (secondary)	3.3%	[0.6%, 7.1%]	8
Improvements ✅ (primary)	-3.4%	[-3.4%, -3.4%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.7%	[-3.4%, 5.9%]	24

Cycles

Results (primary 3.4%, secondary 2.5%)

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

	mean	range	count
Regressions ❌ (primary)	3.4%	[2.1%, 9.0%]	28
Regressions ❌ (secondary)	2.5%	[1.4%, 4.4%]	30
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	3.4%	[2.1%, 9.0%]	28

Binary size

Results (primary 0.2%, secondary 0.2%)

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

	mean	range	count
Regressions ❌ (primary)	0.2%	[0.0%, 1.1%]	124
Regressions ❌ (secondary)	0.2%	[0.0%, 2.1%]	157
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.2%	[0.0%, 1.1%]	124

Bootstrap: 457.604s -> 457.673s (0.02%)
Artifact size: 398.89 MiB -> 398.95 MiB (0.02%)

lcnr · 2026-08-21T14:24:58Z

closing in favor of #161457

rustbot assigned lcnr Apr 30, 2026

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rust-bors Bot pushed a commit that referenced this pull request Apr 30, 2026

Auto merge of #156018 - nia-e:move-trait, r=<try>

ad7b56e

implement `Move` trait prototype

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lcnr reviewed May 1, 2026

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Comment thread compiler/rustc_borrowck/src/type_check/mod.rs Outdated

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Comment thread compiler/rustc_hir_analysis/src/check/wfcheck.rs Outdated

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Comment thread compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs Outdated

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nia-e force-pushed the move-trait branch from 43e14bd to 97218d3 Compare May 4, 2026 08:21

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rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jul 24, 2026

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rust-bors Bot pushed a commit that referenced this pull request Jul 24, 2026

Auto merge of #156018 - nia-e:move-trait, r=<try>

b373540

implement `Move` trait prototype

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lcnr mentioned this pull request Jul 31, 2026

Immobile types and guaranteed destructors rust-lang/goals#635

Open

zannabianca1997 mentioned this pull request Aug 5, 2026

handled ubiqutous Move bounds printing nia-e/rust#1

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nia-e added 2 commits August 21, 2026 11:37

fallible type ops

cf35ba7

move trait

b26f1a9

lcnr force-pushed the move-trait branch from 88b54c9 to b26f1a9 Compare August 21, 2026 10:07

rustbot added the A-attributes Area: Attributes (`#[…]`, `#![…]`) label Aug 21, 2026

zannabianca1997 added 2 commits August 21, 2026 12:10

Fix: removed Move from being printed at all

f8a03a4

it should give some info tho...

Fix: assume Move when the move_trait feature is not added

e7f8fab

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rust-bors Bot pushed a commit that referenced this pull request Aug 21, 2026

Auto merge of #156018 - nia-e:move-trait, r=<try>

a238f16

implement `Move` trait prototype

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zannabianca1997 mentioned this pull request Aug 21, 2026

Move trait prototype #161457

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Aug 21, 2026

lcnr closed this Aug 21, 2026

rustbot removed the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Aug 21, 2026

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nia-e commented Apr 30, 2026 • edited by lcnr Loading Uh oh! There was an error while loading. Please reload this page.

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TODO

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