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Consider principal trait ref's auto-trait super-traits in dyn upcasting #119338
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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; | |||
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// All of a's auto traits need to be in b's auto traits. |
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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(); |
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Please review this code with whitespace disabled.
.filter(|def_id| self.tcx().trait_is_auto(*def_id)) | ||
})) | ||
.collect(); | ||
let auto_traits_compatible = b_data |
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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.
@bors try @rust-timer queue |
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…=<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. ```
☀️ Try build successful - checks-actions |
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Finished benchmarking commit (82115ba): comparison URL. Overall result: no relevant changes - no action neededBenchmarking 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 Instruction countThis benchmark run did not return any relevant results for this metric. Max RSS (memory usage)ResultsThis 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.
CyclesResultsThis 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.
Binary sizeThis benchmark run did not return any relevant results for this metric. Bootstrap: 671.325s -> 671.846s (0.08%) |
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Could you add a similar test to Miri? (src/tools/miri/tests/pass
)
This seems like a no-brainer, assuming that crater is happy? It would be consistent with the other normalizations that |
r? @lcnr |
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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?
OK, I guess I'd also rather just elaborate the super-auto-traits eagerly. That's not hard to impl. |
☔ The latest upstream changes (presumably #120251) made this pull request unmergeable. Please resolve the merge conflicts. |
🔔 This is now entering its final comment period, as per the review above. 🔔 |
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☔ The latest upstream changes (presumably #120862) made this pull request unmergeable. Please resolve the merge conflicts. |
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. |
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rebased @bors r=lcnr |
☀️ Test successful - checks-actions |
Finished benchmarking commit (b656f51): comparison URL. Overall result: ❌ regressions - no action needed@rustbot label: -perf-regression Instruction countThis is a highly reliable metric that was used to determine the overall result at the top of this comment.
Max RSS (memory usage)This benchmark run did not return any relevant results for this metric. CyclesResultsThis 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.
Binary sizeThis benchmark run did not return any relevant results for this metric. Bootstrap: 636.031s -> 639.504s (0.55%) |
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-%26Stdin) - [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%3CTryReserveError%3E-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#120594) 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)
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`
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`
Given traits like:
We should be able to upcast
dyn Subtrait
todyn 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 hasSend
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 implementSend
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 thatdyn Subtrait
is elaborated into the same type ofdyn Subtrait + Send
.I'm open to considering this solution instead, but it would break coherence in the following example: