`Move` trait prototype by zannabianca1997 · Pull Request #161457 · rust-lang/rust

zannabianca1997 · 2026-08-21T12:23:02Z

Finishing the work started by @nia-e in #156018 :

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
fix mangling of Move bounds
how to handle empty trait object that now are dyn Move
also make sure rustdoc handles move correctly
valuable to look into why diesel regresses

r? lcnr

rustbot · 2026-08-21T12:23:08Z

Thanks for the pull request, and welcome! The Rust Project has assigned @lcnr (or someone else) to review your changes, you should hear from them (or someone else) within the next two weeks.

Please see the contribution instructions for more information.

zannabianca1997 · 2026-08-21T19:11:02Z

A quick ./x.py test tests/ui locally to have a baseline

test result: FAILED. 9 passed; 206 failed; 21862 ignored; 0 measured; 0 filtered out; finished in 1.14s

zannabianca1997 · 2026-08-21T21:14:12Z

test result: FAILED. 21801 passed; 32 failed; 244 ignored; 0 measured; 0 filtered out; finished in 168.70s

wow that were a lot of them. looks like the next batch is a bunch of fn that now has fn() + Move

zannabianca1997 · 2026-08-22T13:40:24Z

looking at the errors, there is also a bunch of (dyn + 'static) printing.

Those are all checks going around the trait_alias feature, that created before empty trait object and now creates what are effectively dyn Move, that are being misprinted.

That sure raises a question - can we handle them now? ummm - putting this aside in favour of lower hanging fruits

zannabianca1997 · 2026-08-22T18:13:58Z

@lcnr this last one (520bc2f)

it's better to break the ABI and accept all aymbol mangling containing Move or we have to decide a way to mangle ?Move? I know rust has no stable abi but to put it in all symbols seems a bit too much

it should give some info tho...

Oh wow that got done with A LOT of tests

This is one of the two options, the other being break ABI. I suspect we can do it, Rust not having a stable one (?)

mostly to avoid adding to every single dynamic symbol the `+ Move`

the output uses the debug print and parses it with regex fixed the regex to fetch the first trait, instead of Move

I am _almost_ sure this is what nia wanted to write. I am modifying the behaviour, but I don't see how should it be different, as Move enters now the implicit trait group

missing

rust-log-analyzer · 2026-08-24T21:22:52Z

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' (19184) panicked at library/coretests/tests/mem/type_info.rs:364:9:
assertion `left == right` failed: unexpected ids.
actual: [TypeId(0x46d97972f53f3a183bf0c568812c5dc0), TypeId(0x80dd23405392ff88e3ce17c1f09cd246)]
expected: [TypeId(0x5c957fa7bcd979a4f9ac3180d4a0894f)]
  left: {TypeId(0x46d97972f53f3a183bf0c568812c5dc0), TypeId(0x80dd23405392ff88e3ce17c1f09cd246)}
 right: {TypeId(0x5c957fa7bcd979a4f9ac3180d4a0894f)}
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.

lcnr · 2026-08-28T13:31:54Z


        // We don't support empty trait objects.
-        if regular_traits.is_empty() && auto_traits.is_empty() {
+        if regular_traits.iter().all(|t| tcx.is_implicit_trait(t.0.skip_binder().def_id(), false))


hmm, feel like this can just be regular_traits.chain(auto_traits).all(is_implicit_trait)

also existing, but can you replace the bool of is_implicit_trait wth an enum, e.g.

enum WhateverThisfunctionwants { Yes, No, } *[View changes since the review](https://triagebot.infra.rust-lang.org/gh-changes-since/rust-lang/rust/161457/9a4ad59ae3073b013cd62f53f8349ddc61a012e8..5a6f61532811493d3a1fd88aecf71ce42594ec2e)*

lcnr · 2026-08-28T13:34:40Z

                write!(self, " + ")?;
            }
+            first = false;
            write!(self, "PointeeSized")?;


do we want somethign like... we do repeat this pattern a lot

let mut first = false; let mut print_bound = |bound| { if !first { write!(self, " + ")?; first = false; } self.write_str(bound) }; *[View changes since the review](https://triagebot.infra.rust-lang.org/gh-changes-since/rust-lang/rust/161457/9a4ad59ae3073b013cd62f53f8349ddc61a012e8..5a6f61532811493d3a1fd88aecf71ce42594ec2e)*

lcnr · 2026-08-28T13:37:21Z

+            .collect()
+    } else {
+        clauses.into_iter().collect()
+    };


that one is unfortunately somewhat problematic. gather_explicit_clauses_of is used by a query whose result we write to crate metadata, so this would erase the Move bound from upstream crates which don't have the feature enabled.

Why is this needed

View changes since the review

rust-bors · 2026-08-28T14:57:41Z

☔ The latest upstream changes (presumably #161906) made this pull request unmergeable. Please resolve the merge conflicts by rebasing.

rustbot assigned lcnr Aug 21, 2026

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lcnr mentioned this pull request Aug 21, 2026

implement Move trait prototype #156018

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lcnr changed the title ~~Move trait prototype~~ Move trait prototype Aug 21, 2026

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nia-e and others added 10 commits August 23, 2026 20:56

fallible type ops

dfad1ae

move trait

73f62f5

Fix: removed Move from being printed at all

26a6d54

it should give some info tho...

Fix: assume Move when the move_trait feature is not added

ab6a1d3

Fix: preferred printing of ?Move instead of Move

ea4b10b

Oh wow that got done with A LOT of tests

Feat: removed Move from mangled symbols

48d496a

This is one of the two options, the other being break ABI. I suspect we can do it, Rust not having a stable one (?)

Feat: mangling of ?Move bounds

b188556

mostly to avoid adding to every single dynamic symbol the `+ Move`

Fix: legacy mangler (Fn printer)

a1f7227

Fix: normalized test

03562be

the output uses the debug print and parses it with regex fixed the regex to fetch the first trait, instead of Move

Fix: correctly refusing trait objects that have only Move as a bound

30609e6

zannabianca1997 force-pushed the move-trait branch from 33dfdac to 30609e6 Compare August 23, 2026 19:01

zannabianca1997 added 2 commits August 23, 2026 21:06

Fix: line number drift

f8550b4

Fix: added now present Move clause

7c03c65

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Fix: missing Move pattern

50f804a

I am _almost_ sure this is what nia wanted to write. I am modifying the behaviour, but I don't see how should it be different, as Move enters now the implicit trait group

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Fix: removed the move clause from explicit clauses when the feature is

5a6f615

missing

lcnr reviewed Aug 28, 2026

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TODO

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zannabianca1997 commented Aug 21, 2026 •

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