Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Consider principal trait ref's auto-trait super-traits in dyn upcasting #119338

Merged
merged 1 commit into from
Feb 15, 2024

Conversation

compiler-errors
Copy link
Member

@compiler-errors compiler-errors commented Dec 27, 2023

Given traits like:

trait Subtrait: Supertrait   Send {}
trait Supertrait {}

We should be able to upcast dyn Subtrait to dyn Supertrait Send. This is not currently possible, because when upcasting, we look at the list of auto traits in the object type (dyn Subtrait, which has no auto traits in its bounds) and compare them to the target's auto traits (dyn Supertrait Send, which has Send in its bound).

Since the target has auto traits that are not present in the source, the upcasting fails. This is overly restrictive, since dyn Subtrait will always implement Send via its built-in object impl. I propose to loosen this restriction here.

r? types


Aside: Fix this in astconv instead?

edit: This causes too many failures. See #119825 (comment)

We may also fix this by by automatically elaborating all auto-trait supertraits during AstConv::conv_object_ty_poly_trait_ref. That is, we can make it so that dyn Subtrait is elaborated into the same type of dyn Subtrait Send.

I'm open to considering this solution instead, but it would break coherence in the following example:

trait Foo: Send {}

trait Bar {}
impl Bar for dyn Foo {}
impl Bar for dyn Foo   Send {}
//~^ This would begin to be an overlapping impl.

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. WG-trait-system-refactor The Rustc Trait System Refactor Initiative labels Dec 27, 2023
@rustbot
Copy link
Collaborator

rustbot commented Dec 27, 2023

Some changes occurred to the core trait solver

cc @rust-lang/initiative-trait-system-refactor

@@ -644,13 647,6 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
let tcx = self.tcx();
let Goal { predicate: (a_ty, _b_ty), .. } = goal;

// All of a's auto traits need to be in b's auto traits.
Copy link
Member Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

This check is redundant.

let principal_def_id_b = b_data.principal_def_id();
if principal_def_id_a == principal_def_id_b {
// no cyclic
let principal_def_id_a = a_data.principal_def_id();
Copy link
Member Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Please review this code with whitespace disabled.

.filter(|def_id| self.tcx().trait_is_auto(*def_id))
}))
.collect();
let auto_traits_compatible = b_data
Copy link
Member Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

This auto_traits_compatible check is only necessary for the principal_def_id_a == principal_def_id_b case. The match_upcast_principal function checks auto traits itself.

@compiler-errors compiler-errors added the needs-fcp This change is insta-stable, so needs a completed FCP to proceed. label Dec 27, 2023
@compiler-errors
Copy link
Member Author

@bors try @rust-timer queue

@rust-timer

This comment has been minimized.

@rustbot rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Dec 27, 2023
@bors
Copy link
Contributor

bors commented Dec 27, 2023

⌛ Trying commit 6cfde57 with merge 82115ba...

bors added a commit to rust-lang-ci/rust that referenced this pull request Dec 27, 2023
…=<try>

Consider principal trait ref's auto-trait super-traits in dyn upcasting

Given traits like:

```rust
trait Subtrait: Supertrait   Send {}
trait Supertrait {}
```

We should be able to upcast `dyn Subtrait` to `dyn Supertrait   Send`. This is not currently possible, because when upcasting, we look at the list of auto traits in the object type (`dyn Subtrait`, which has no auto traits in its bounds) and compare them to the target's auto traits (`dyn Supertrait   Send`, which has `Send` in its bound).

Since the target has auto traits that are not present in the source, the upcasting fails. This is overly restrictive, since `dyn Subtrait` will always implement `Send` via its built-in object impl. I propose to loosen this restriction here.

r? types

---

### Aside: Fix this in astconv instead?

We may also fix this by by automatically elaborating all auto-trait supertraits during `AstConv::conv_object_ty_poly_trait_ref`. That is, we can make it so that `dyn Subtrait` is elaborated into the same type of `dyn Subtrait   Send`. I'm open to considering this solution, but it would break coherence:

```rust
trait Foo: Send {}

trait Bar {}
impl Bar for dyn Foo {}
impl Bar for dyn Foo   Send {}
//~^ This would begin to be an overlapping impl.
```
@compiler-errors compiler-errors added T-types Relevant to the types team, which will review and decide on the PR/issue. and removed T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Dec 27, 2023
@bors
Copy link
Contributor

bors commented Dec 27, 2023

☀️ Try build successful - checks-actions
Build commit: 82115ba (82115bac2b802bf307220d2d14b5d970ac833e4f)

@rust-timer

This comment has been minimized.

@rust-timer
Copy link
Collaborator

Finished benchmarking commit (82115ba): comparison URL.

Overall result: no relevant changes - no action needed

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

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

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

mean range count
Regressions ❌
(primary)
- - 0
Regressions ❌
(secondary)
- - 0
Improvements ✅
(primary)
-0.6% [-0.6%, -0.6%] 1
Improvements ✅
(secondary)
-1.9% [-1.9%, -1.9%] 1
All ❌✅ (primary) -0.6% [-0.6%, -0.6%] 1

Cycles

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

mean range count
Regressions ❌
(primary)
- - 0
Regressions ❌
(secondary)
2.9% [2.9%, 2.9%] 1
Improvements ✅
(primary)
-0.5% [-0.5%, -0.5%] 1
Improvements ✅
(secondary)
- - 0
All ❌✅ (primary) -0.5% [-0.5%, -0.5%] 1

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 671.325s -> 671.846s (0.08%)
Artifact size: 312.40 MiB -> 312.39 MiB (-0.00%)

@rustbot rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Dec 27, 2023
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Could you add a similar test to Miri? (src/tools/miri/tests/pass)

@Jules-Bertholet
Copy link
Contributor

We may also fix this by by automatically elaborating all auto-trait supertraits during AstConv::conv_object_ty_poly_trait_ref. That is, we can make it so that dyn Subtrait is elaborated into the same type of dyn Subtrait Send.

This seems like a no-brainer, assuming that crater is happy? It would be consistent with the other normalizations that dyn does (dyn Foo Send = dyn Send Foo = dyn Foo Send Send = trait Bar = Foo Send; dyn Bar).

@lcnr
Copy link
Contributor

lcnr commented Jan 8, 2024

r? @lcnr

@rustbot rustbot assigned lcnr and unassigned jackh726 Jan 8, 2024
Copy link
Contributor

@lcnr lcnr left a comment

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

lgtm after adding a run-pass test (and miri), which is what @RalfJung is asking for.

I am personally slightly in favor of elaborating super traits eagerly and (maybe) linting if they are explicitly mentioned even though they are implied. Would you mind implementing that and running crater?

I guess that's a t-lang question?

@compiler-errors
Copy link
Member Author

OK, I guess I'd also rather just elaborate the super-auto-traits eagerly. That's not hard to impl.

@bors
Copy link
Contributor

bors commented Jan 23, 2024

☔ The latest upstream changes (presumably #120251) made this pull request unmergeable. Please resolve the merge conflicts.

@rfcbot rfcbot added final-comment-period In the final comment period and will be merged soon unless new substantive objections are raised. and removed proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. labels Feb 5, 2024
@rfcbot
Copy link

rfcbot commented Feb 5, 2024

🔔 This is now entering its final comment period, as per the review above. 🔔

@bors
Copy link
Contributor

bors commented Feb 10, 2024

☔ The latest upstream changes (presumably #120862) made this pull request unmergeable. Please resolve the merge conflicts.

@rfcbot rfcbot added finished-final-comment-period The final comment period is finished for this PR / Issue. and removed final-comment-period In the final comment period and will be merged soon unless new substantive objections are raised. labels Feb 15, 2024
@rfcbot
Copy link

rfcbot commented Feb 15, 2024

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

This will be merged soon.

@rfcbot rfcbot added the to-announce Announce this issue on triage meeting label Feb 15, 2024
@compiler-errors
Copy link
Member Author

rebased

@bors r=lcnr

@bors
Copy link
Contributor

bors commented Feb 15, 2024

📌 Commit ec8e898 has been approved by lcnr

It is now in the queue for this repository.

@bors bors 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 Feb 15, 2024
@bors
Copy link
Contributor

bors commented Feb 15, 2024

⌛ Testing commit ec8e898 with merge b656f51...

@apiraino apiraino removed the to-announce Announce this issue on triage meeting label Feb 15, 2024
@bors
Copy link
Contributor

bors commented Feb 15, 2024

☀️ Test successful - checks-actions
Approved by: lcnr
Pushing b656f51 to master...

@bors bors added the merged-by-bors This PR was explicitly merged by bors. label Feb 15, 2024
@bors bors merged commit b656f51 into rust-lang:master Feb 15, 2024
12 checks passed
@rustbot rustbot added this to the 1.78.0 milestone Feb 15, 2024
@rust-timer
Copy link
Collaborator

Finished benchmarking commit (b656f51): comparison URL.

Overall result: ❌ regressions - no action needed

@rustbot label: -perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

mean range count
Regressions ❌
(primary)
- - 0
Regressions ❌
(secondary)
7.7% [7.7%, 7.7%] 1
Improvements ✅
(primary)
- - 0
Improvements ✅
(secondary)
- - 0
All ❌✅ (primary) - - 0

Max RSS (memory usage)

This benchmark run did not return any relevant results for this metric.

Cycles

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

mean range count
Regressions ❌
(primary)
- - 0
Regressions ❌
(secondary)
5.1% [5.1%, 5.1%] 1
Improvements ✅
(primary)
- - 0
Improvements ✅
(secondary)
- - 0
All ❌✅ (primary) - - 0

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 636.031s -> 639.504s (0.55%)
Artifact size: 306.32 MiB -> 306.30 MiB (-0.01%)

wip-sync pushed a commit to NetBSD/pkgsrc-wip that referenced this pull request May 4, 2024
Pkgsrc changes:
 * Adapt checksums and patches, some have beene intregrated upstream.

Upstream chnages:

Version 1.78.0 (2024-05-02)
===========================

Language
--------
- [Stabilize `#[cfg(target_abi = ...)]`]
  (rust-lang/rust#119590)
- [Stabilize the `#[diagnostic]` namespace and
  `#[diagnostic::on_unimplemented]` attribute]
  (rust-lang/rust#119888)
- [Make async-fn-in-trait implementable with concrete signatures]
  (rust-lang/rust#120103)
- [Make matching on NaN a hard error, and remove the rest of
  `illegal_floating_point_literal_pattern`]
  (rust-lang/rust#116284)
- [static mut: allow mutable reference to arbitrary types, not just
  slices and arrays]
  (rust-lang/rust#117614)
- [Extend `invalid_reference_casting` to include references casting
  to bigger memory layout]
  (rust-lang/rust#118983)
- [Add `non_contiguous_range_endpoints` lint for singleton gaps
  after exclusive ranges]
  (rust-lang/rust#118879)
- [Add `wasm_c_abi` lint for use of older wasm-bindgen versions]
  (rust-lang/rust#117918)
  This lint currently only works when using Cargo.
- [Update `indirect_structural_match` and `pointer_structural_match`
  lints to match RFC]
  (rust-lang/rust#120423)
- [Make non-`PartialEq`-typed consts as patterns a hard error]
  (rust-lang/rust#120805)
- [Split `refining_impl_trait` lint into `_reachable`, `_internal` variants]
  (rust-lang/rust#121720)
- [Remove unnecessary type inference when using associated types
  inside of higher ranked `where`-bounds]
  (rust-lang/rust#119849)
- [Weaken eager detection of cyclic types during type inference]
  (rust-lang/rust#119989)
- [`trait Trait: Auto {}`: allow upcasting from `dyn Trait` to `dyn Auto`]
  (rust-lang/rust#119338)

Compiler
--------

- [Made `INVALID_DOC_ATTRIBUTES` lint deny by default]
  (rust-lang/rust#111505)
- [Increase accuracy of redundant `use` checking]
  (rust-lang/rust#117772)
- [Suggest moving definition if non-found macro_rules! is defined later]
  (rust-lang/rust#121130)
- [Lower transmutes from int to pointer type as gep on null]
  (rust-lang/rust#121282)

Target changes:

- [Windows tier 1 targets now require at least Windows 10]
  (rust-lang/rust#115141)
 - [Enable CMPXCHG16B, SSE3, SAHF/LAHF and 128-bit Atomics in tier 1 Windows]
  (rust-lang/rust#120820)
- [Add `wasm32-wasip1` tier 2 (without host tools) target]
  (rust-lang/rust#120468)
- [Add `wasm32-wasip2` tier 3 target]
  (rust-lang/rust#119616)
- [Rename `wasm32-wasi-preview1-threads` to `wasm32-wasip1-threads`]
  (rust-lang/rust#122170)
- [Add `arm64ec-pc-windows-msvc` tier 3 target]
  (rust-lang/rust#119199)
- [Add `armv8r-none-eabihf` tier 3 target for the Cortex-R52]
  (rust-lang/rust#110482)
- [Add `loongarch64-unknown-linux-musl` tier 3 target]
  (rust-lang/rust#121832)

Refer to Rust's [platform support page][platform-support-doc]
for more information on Rust's tiered platform support.

Libraries
---------

- [Bump Unicode to version 15.1.0, regenerate tables]
  (rust-lang/rust#120777)
- [Make align_offset, align_to well-behaved in all cases]
  (rust-lang/rust#121201)
- [PartialEq, PartialOrd: document expectations for transitive chains]
  (rust-lang/rust#115386)
- [Optimize away poison guards when std is built with panic=abort]
  (rust-lang/rust#100603)
- [Replace pthread `RwLock` with custom implementation]
  (rust-lang/rust#110211)
- [Implement unwind safety for Condvar on all platforms]
  (rust-lang/rust#121768)
- [Add ASCII fast-path for `char::is_grapheme_extended`]
  (rust-lang/rust#121138)

Stabilized APIs
---------------

- [`impl Read for &Stdin`]
  (https://doc.rust-lang.org/stable/std/io/struct.Stdin.html#impl-Read-for-&Stdin)
- [Accept non `'static` lifetimes for several `std::error::Error`
  related implementations] (rust-lang/rust#113833)
- [Make `impl<Fd: AsFd>` impl take `?Sized`]
  (rust-lang/rust#114655)
- [`impl From<TryReserveError> for io::Error`]
  (https://doc.rust-lang.org/stable/std/io/struct.Error.html#impl-From-for-Error)

These APIs are now stable in const contexts:

- [`Barrier::new()`]
  (https://doc.rust-lang.org/stable/std/sync/struct.Barrier.html#method.new)

Cargo
-----

- [Stabilize lockfile v4](rust-lang/cargo#12852)
- [Respect `rust-version` when generating lockfile]
  (rust-lang/cargo#12861)
- [Control `--charset` via auto-detecting config value]
  (rust-lang/cargo#13337)
- [Support `target.<triple>.rustdocflags` officially]
  (rust-lang/cargo#13197)
- [Stabilize global cache data tracking]
  (rust-lang/cargo#13492)

Misc
----

- [rustdoc: add `--test-builder-wrapper` arg to support wrappers
  such as RUSTC_WRAPPER when building doctests]
  (rust-lang/rust#114651)

Compatibility Notes
-------------------

- [Many unsafe precondition checks now run for user code with debug
  assertions enabled] (rust-lang/rust#120863)
  This change helps users catch undefined behavior in their code,
  though the details of how much is checked are generally not
  stable.
- [riscv only supports split_debuginfo=off for now]
  (rust-lang/rust#120518)
- [Consistently check bounds on hidden types of `impl Trait`]
  (rust-lang/rust#121679)
- [Change equality of higher ranked types to not rely on subtyping]
  (rust-lang/rust#118247)
- [When called, additionally check bounds on normalized function return type]
  (rust-lang/rust#118882)
- [Expand coverage for `arithmetic_overflow` lint]
  (rust-lang/rust#119432)

Internal Changes
----------------

These changes do not affect any public interfaces of Rust, but they represent
significant improvements to the performance or internals of rustc and related
tools.

- [Update to LLVM 18](rust-lang/rust#120055)
- [Build `rustc` with 1CGU on `x86_64-pc-windows-msvc`]
  (rust-lang/rust#112267)
- [Build `rustc` with 1CGU on `x86_64-apple-darwin`]
  (rust-lang/rust#112268)
- [Introduce `run-make` V2 infrastructure, a `run_make_support`
  library and port over 2 tests as example]
  (rust-lang/rust#113026)
- [Windows: Implement condvar, mutex and rwlock using futex]
  (rust-lang/rust#121956)
workingjubilee added a commit to workingjubilee/rustc that referenced this pull request Jun 12, 2024
fix RELEASES: we do not support upcasting to auto traits

rust-lang#119338 does not actually support casts from `dyn Trait` to `dyn Auto`, only from `dyn Trait` to `dyn Trait   Auto`. The following test does not compile

```rust
trait Trait: Send {}
impl<T: Send> Trait for T {}

fn foo() {
    let x: &i32 = &1;
    let y = x as &dyn Trait as &dyn Send;
}
```
it actually also doesn't compile with `feature(trait_upcasting)`, opened rust-lang#126313 for that

r? `@Mark-Simulacrum` `@cuviper`
rust-timer added a commit to rust-lang-ci/rust that referenced this pull request Jun 12, 2024
Rollup merge of rust-lang#126314 - lcnr:fix-relnotes, r=pietroalbini

fix RELEASES: we do not support upcasting to auto traits

rust-lang#119338 does not actually support casts from `dyn Trait` to `dyn Auto`, only from `dyn Trait` to `dyn Trait   Auto`. The following test does not compile

```rust
trait Trait: Send {}
impl<T: Send> Trait for T {}

fn foo() {
    let x: &i32 = &1;
    let y = x as &dyn Trait as &dyn Send;
}
```
it actually also doesn't compile with `feature(trait_upcasting)`, opened rust-lang#126313 for that

r? `@Mark-Simulacrum` `@cuviper`
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
Labels
disposition-merge This issue / PR is in PFCP or FCP with a disposition to merge it. finished-final-comment-period The final comment period is finished for this PR / Issue. merged-by-bors This PR was explicitly merged by bors. needs-fcp This change is insta-stable, so needs a completed FCP to proceed. S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. T-types Relevant to the types team, which will review and decide on the PR/issue. WG-trait-system-refactor The Rustc Trait System Refactor Initiative
Projects
None yet
Development

Successfully merging this pull request may close these issues.

None yet

10 participants