impl DispatchFromDyn for Cell and UnsafeCell #97373

dimpolo · 2022-05-24T22:18:00Z

After some fruitful discussion on Internals here's my first PR to rust-lang/rust 🎉

Please let me know if there's something I missed.

This adds DispatchFromDyn impls for Cell, UnsafeCell and SyncUnsafeCell.
An existing test is also expanded to test the Cell impl (which requires the UnsafeCell impl)

The different RefCell types can not implement DispatchFromDyn since they have more than one (non ZST) field.

Edit:

What:

These changes allow one to make types like MyRc(code below), to be object safe method receivers after implementing DispatchFromDyn and Deref for them.

This allows for code like this:

struct MyRc<T: ?Sized>(Cell<NonNull<RcBox<T>>>);

/* impls for DispatchFromDyn, CoerceUnsized and Deref for MyRc*/

trait Trait {
    fn foo(self: MyRc<Self>);
}

let impls_trait = ...;
let rc = MyRc::new(impls_trait) as MyRc<dyn Trait>;
rc.foo();

Note: Cell and UnsafeCell won't directly become valid method receivers since they don't implement Deref. Making use of these changes requires a wrapper type and nightly features.

Why:

A custom pointer type with interior mutability allows one to store extra information in the pointer itself.
These changes allow for such a type to be a method receiver.

Examples:

My use case is a cycle aware custom Rc implementation that when dropping a cycle marks some references dangling.

On the forum andersk mentioned that they track if a Gc reference is rooted with an extra bit in the reference itself.

rust-highfive · 2022-05-24T22:18:03Z

Hey! It looks like you've submitted a new PR for the library teams!

If this PR contains changes to any rust-lang/rust public library APIs then please comment with r? rust-lang/libs-api @rustbot label +T-libs-api -T-libs to request review from a libs-api team reviewer. If you're unsure where your change falls no worries, just leave it as is and the reviewer will take a look and make a decision to forward on if necessary.

Examples of T-libs-api changes:

Stabilizing library features
Introducing insta-stable changes such as new implementations of existing stable traits on existing stable types
Introducing new or changing existing unstable library APIs (excluding permanently unstable features / features without a tracking issue)
Changing public documentation in ways that create new stability guarantees
Changing observable runtime behavior of library APIs

rust-highfive · 2022-05-24T22:18:04Z

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @thomcc (or someone else) soon.

Please see the contribution instructions for more information.

thomcc · 2022-05-24T22:23:54Z

r? rust-lang/libs-api @rustbot label +T-libs-api -T-libs

thomcc · 2022-05-24T23:18:35Z

After some fruitful discussion on Internals

Is this the right link? There are no comments on it.

dimpolo · 2022-05-24T23:28:32Z

Sorry, I should learn that my humour doesn't translate well into text..

Nobody commented, so I thought I'll give this one a try myself :)

dimpolo · 2022-06-18T18:55:17Z

Would it be fair to ping?

The changes should be uncontroversial hopefully.

Implementing DispatchFromDyn enables a type to be used as a self type, if that type also implements Deref. Since Cell and UnsafeCell don't implement Deref actually making use of these changes requires a custom wrapper type and nighty features (as is shown in the test).

m-ou-se · 2022-06-20T11:53:54Z

@rfcbot merge

rfcbot · 2022-06-20T12:26:28Z

Team member @m-ou-se has proposed to merge this. The next step is review by the rest of the tagged team members:

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

BurntSushi · 2022-06-29T23:28:48Z

Implementing DispatchFromDyn enables a type to be used as a self type

Does this mean we should rope the @rust-lang/lang team in on this? I know this is technically adding trait impls and that's libs-api, but this bit makes it sound like the trait impls are actually just a mechanism for a language hook. Increasing the set of types that can be Self types seems like a lang change?

tmandry · 2022-12-06T19:49:51Z

src/test/ui/feature-gates/feature-gate-dispatch-from-dyn-cell.rs

+trait Trait{
+    fn cell(self: Cell<&Self>); //~ ERROR invalid `self` parameter type: Cell<&Self>
+}
+


Suggested change

trait Trait2 {

fn cell(self: Cell<Self>); //~ ERROR invalid `self` parameter type: Cell<Self>

}

Would this make sense to add?

If you'd like I'll add.

I don't see what it would be testing though.
I chose Cell<&Self> in the test because it could, at least in theory, provide access to &Self.
Cell<Self> is not able to provide &Self.

rfcbot · 2022-12-16T19:48:07Z

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.

dimpolo · 2023-01-24T15:19:51Z

Rebased to:

move tests from test/ to tests/
update a .stderr file

dimpolo · 2023-01-25T16:00:33Z

This will be merged soon.
Dec 16, 2022

Is something holding up the merge?

dtolnay · 2023-01-25T20:38:08Z

@bors r+

bors · 2023-01-25T20:38:11Z

📌 Commit af58854 has been approved by dtolnay

It is now in the queue for this repository.

…iaskrgr Rollup of 9 pull requests Successful merges: - rust-lang#97373 (impl DispatchFromDyn for Cell and UnsafeCell) - rust-lang#106625 (Remove backwards compat for LLVM 12 coverage format) - rust-lang#106779 (Avoid __cxa_thread_atexit_impl on Emscripten) - rust-lang#106811 (Append .dwp to the binary filename instead of replacing the existing extension.) - rust-lang#106836 (Remove optimistic spinning from `mpsc::SyncSender`) - rust-lang#106946 (implement Hash for proc_macro::LineColumn) - rust-lang#107074 (remove unnecessary check for opaque types) - rust-lang#107287 (Improve fn pointer notes) - rust-lang#107304 (Use `can_eq` to compare types for default assoc type error) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup

This requires #![feature(arbitrary_self_types)] and nightly 2023-01-27 or later for rust-lang/rust#97373. Signed-off-by: Anders Kaseorg <[email protected]>

Pkgsrc changes: * Adjust patches and cargo checksums to new versions. * Sadly, the patch to reduce the cargo verbosity no longer applies, so I've asked upstream about the proper way to get the old result. (so the build log becomes Quite Bloated for now). Upstream changes: Version 1.69.0 (2023-04-20) ========================== Language -------- - [Deriving built-in traits on packed structs works with `Copy` fields.] (rust-lang/rust#104429) - [Stabilize the `cmpxchg16b` target feature on x86 and x86_64.] (rust-lang/rust#106774) - [Improve analysis of trait bounds for associated types.] (rust-lang/rust#103695) - [Allow associated types to be used as union fields.] (rust-lang/rust#106938) - [Allow `Self: Autotrait` bounds on dyn-safe trait methods.] (rust-lang/rust#107082) - [Treat `str` as containing `[u8]` for auto trait purposes.] (rust-lang/rust#107941) Compiler -------- - [Upgrade `*-pc-windows-gnu` on CI to mingw-w64 v10 and GCC 12.2.] (rust-lang/rust#100178) - [Rework min_choice algorithm of member constraints.] (rust-lang/rust#105300) - [Support `true` and `false` as boolean flags in compiler arguments.] (rust-lang/rust#107043) - [Default `repr(C)` enums to `c_int` size.] (rust-lang/rust#107592) Libraries --------- - [Implement the unstable `DispatchFromDyn` for cell types, allowing downstream experimentation with custom method receivers.] (rust-lang/rust#97373) - [Document that `fmt::Arguments::as_str()` may return `Some(_)` in more cases after optimization, subject to change.] (rust-lang/rust#106823) - [Implement `AsFd` and `AsRawFd` for `Rc`.] (rust-lang/rust#107317) Stabilized APIs --------------- - [`CStr::from_bytes_until_nul`] (https://doc.rust-lang.org/stable/core/ffi/struct.CStr.html#method.from_bytes_until_nul) - [`core::ffi::FromBytesUntilNulError`] (https://doc.rust-lang.org/stable/core/ffi/struct.FromBytesUntilNulError.html) These APIs are now stable in const contexts: - [`SocketAddr::new`] (https://doc.rust-lang.org/stable/std/net/enum.SocketAddr.html#method.new) - [`SocketAddr::ip`] (https://doc.rust-lang.org/stable/std/net/enum.SocketAddr.html#method.ip) - [`SocketAddr::port`] (https://doc.rust-lang.org/stable/std/net/enum.SocketAddr.html#method.port) - [`SocketAddr::is_ipv4`] (https://doc.rust-lang.org/stable/std/net/enum.SocketAddr.html#method.is_ipv4) - [`SocketAddr::is_ipv6`] (https://doc.rust-lang.org/stable/std/net/enum.SocketAddr.html#method.is_ipv6) - [`SocketAddrV4::new`] (https://doc.rust-lang.org/stable/std/net/struct.SocketAddrV4.html#method.new) - [`SocketAddrV4::ip`] (https://doc.rust-lang.org/stable/std/net/struct.SocketAddrV4.html#method.ip) - [`SocketAddrV4::port`] (https://doc.rust-lang.org/stable/std/net/struct.SocketAddrV4.html#method.port) - [`SocketAddrV6::new`] (https://doc.rust-lang.org/stable/std/net/struct.SocketAddrV6.html#method.new) - [`SocketAddrV6::ip`] (https://doc.rust-lang.org/stable/std/net/struct.SocketAddrV6.html#method.ip) - [`SocketAddrV6::port`] (https://doc.rust-lang.org/stable/std/net/struct.SocketAddrV6.html#method.port) - [`SocketAddrV6::flowinfo`] (https://doc.rust-lang.org/stable/std/net/struct.SocketAddrV6.html#method.flowinfo) - [`SocketAddrV6::scope_id`] (https://doc.rust-lang.org/stable/std/net/struct.SocketAddrV6.html#method.scope_id) Cargo ----- - [Cargo now suggests `cargo fix` or `cargo clippy --fix` when compilation warnings are auto-fixable.] (rust-lang/cargo#11558) - [Cargo now suggests `cargo add` if you try to install a library crate.] (rust-lang/cargo#11410) - [Cargo now sets the `CARGO_BIN_NAME` environment variable also for binary examples.] (rust-lang/cargo#11705) Rustdoc ----- - [Vertically compact trait bound formatting.] (rust-lang/rust#102842) - [Only include stable lints in `rustdoc::all` group.] (rust-lang/rust#106316) - [Compute maximum Levenshtein distance based on the query.] (rust-lang/rust#107141) - [Remove inconsistently-present sidebar tooltips.] (rust-lang/rust#107490) - [Search by macro when query ends with `!`.] (rust-lang/rust#108143) Compatibility Notes ------------------- - [The `rust-analysis` component from `rustup` now only contains a warning placeholder.] (rust-lang/rust#101841) This was primarily intended for RLS, and the corresponding `-Zsave-analysis` flag has been removed from the compiler as well. - [Unaligned references to packed fields are now a hard error.] (rust-lang/rust#102513) This has been a warning since 1.53, and denied by default with a future-compatibility warning since 1.62. - [Update the minimum external LLVM to 14.] (rust-lang/rust#107573) - [Cargo now emits errors on invalid characters in a registry token.] (rust-lang/cargo#11600) - [When `default-features` is set to false of a workspace dependency, and an inherited dependency of a member has `default-features = true`, Cargo will enable default features of that dependency.] (rust-lang/cargo#11409) - [Cargo denies `CARGO_HOME` in the `[env]` configuration table. Cargo itself doesn't pick up this value, but recursive calls to cargo would, which was not intended.] (rust-lang/cargo#11644) - [Debuginfo for build dependencies is now off if not explicitly set. This is expected to improve the overall build time.] (rust-lang/cargo#11252) 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. - [Move `format_args!()` into AST (and expand it during AST lowering)] (rust-lang/rust#106745)

Pkgsrc changes: * Adjust patches and cargo checksums to new versions. Upstream changes: Version 1.69.0 (2023-04-20) ========================== Language -------- - [Deriving built-in traits on packed structs works with `Copy` fields.] (rust-lang/rust#104429) - [Stabilize the `cmpxchg16b` target feature on x86 and x86_64.] (rust-lang/rust#106774) - [Improve analysis of trait bounds for associated types.] (rust-lang/rust#103695) - [Allow associated types to be used as union fields.] (rust-lang/rust#106938) - [Allow `Self: Autotrait` bounds on dyn-safe trait methods.] (rust-lang/rust#107082) - [Treat `str` as containing `[u8]` for auto trait purposes.] (rust-lang/rust#107941) Compiler -------- - [Upgrade `*-pc-windows-gnu` on CI to mingw-w64 v10 and GCC 12.2.] (rust-lang/rust#100178) - [Rework min_choice algorithm of member constraints.] (rust-lang/rust#105300) - [Support `true` and `false` as boolean flags in compiler arguments.] (rust-lang/rust#107043) - [Default `repr(C)` enums to `c_int` size.] (rust-lang/rust#107592) Libraries --------- - [Implement the unstable `DispatchFromDyn` for cell types, allowing downstream experimentation with custom method receivers.] (rust-lang/rust#97373) - [Document that `fmt::Arguments::as_str()` may return `Some(_)` in more cases after optimization, subject to change.] (rust-lang/rust#106823) - [Implement `AsFd` and `AsRawFd` for `Rc`.] (rust-lang/rust#107317) Stabilized APIs --------------- - [`CStr::from_bytes_until_nul`] (https://doc.rust-lang.org/stable/core/ffi/struct.CStr.html#method.from_bytes_until_nul) - [`core::ffi::FromBytesUntilNulError`] (https://doc.rust-lang.org/stable/core/ffi/struct.FromBytesUntilNulError.html) These APIs are now stable in const contexts: - [`SocketAddr::new`] (https://doc.rust-lang.org/stable/std/net/enum.SocketAddr.html#method.new) - [`SocketAddr::ip`] (https://doc.rust-lang.org/stable/std/net/enum.SocketAddr.html#method.ip) - [`SocketAddr::port`] (https://doc.rust-lang.org/stable/std/net/enum.SocketAddr.html#method.port) - [`SocketAddr::is_ipv4`] (https://doc.rust-lang.org/stable/std/net/enum.SocketAddr.html#method.is_ipv4) - [`SocketAddr::is_ipv6`] (https://doc.rust-lang.org/stable/std/net/enum.SocketAddr.html#method.is_ipv6) - [`SocketAddrV4::new`] (https://doc.rust-lang.org/stable/std/net/struct.SocketAddrV4.html#method.new) - [`SocketAddrV4::ip`] (https://doc.rust-lang.org/stable/std/net/struct.SocketAddrV4.html#method.ip) - [`SocketAddrV4::port`] (https://doc.rust-lang.org/stable/std/net/struct.SocketAddrV4.html#method.port) - [`SocketAddrV6::new`] (https://doc.rust-lang.org/stable/std/net/struct.SocketAddrV6.html#method.new) - [`SocketAddrV6::ip`] (https://doc.rust-lang.org/stable/std/net/struct.SocketAddrV6.html#method.ip) - [`SocketAddrV6::port`] (https://doc.rust-lang.org/stable/std/net/struct.SocketAddrV6.html#method.port) - [`SocketAddrV6::flowinfo`] (https://doc.rust-lang.org/stable/std/net/struct.SocketAddrV6.html#method.flowinfo) - [`SocketAddrV6::scope_id`] (https://doc.rust-lang.org/stable/std/net/struct.SocketAddrV6.html#method.scope_id) Cargo ----- - [Cargo now suggests `cargo fix` or `cargo clippy --fix` when compilation warnings are auto-fixable.] (rust-lang/cargo#11558) - [Cargo now suggests `cargo add` if you try to install a library crate.] (rust-lang/cargo#11410) - [Cargo now sets the `CARGO_BIN_NAME` environment variable also for binary examples.] (rust-lang/cargo#11705) Rustdoc ----- - [Vertically compact trait bound formatting.] (rust-lang/rust#102842) - [Only include stable lints in `rustdoc::all` group.] (rust-lang/rust#106316) - [Compute maximum Levenshtein distance based on the query.] (rust-lang/rust#107141) - [Remove inconsistently-present sidebar tooltips.] (rust-lang/rust#107490) - [Search by macro when query ends with `!`.] (rust-lang/rust#108143) Compatibility Notes ------------------- - [The `rust-analysis` component from `rustup` now only contains a warning placeholder.] (rust-lang/rust#101841) This was primarily intended for RLS, and the corresponding `-Zsave-analysis` flag has been removed from the compiler as well. - [Unaligned references to packed fields are now a hard error.] (rust-lang/rust#102513) This has been a warning since 1.53, and denied by default with a future-compatibility warning since 1.62. - [Update the minimum external LLVM to 14.] (rust-lang/rust#107573) - [Cargo now emits errors on invalid characters in a registry token.] (rust-lang/cargo#11600) - [When `default-features` is set to false of a workspace dependency, and an inherited dependency of a member has `default-features = true`, Cargo will enable default features of that dependency.] (rust-lang/cargo#11409) - [Cargo denies `CARGO_HOME` in the `[env]` configuration table. Cargo itself doesn't pick up this value, but recursive calls to cargo would, which was not intended.] (rust-lang/cargo#11644) - [Debuginfo for build dependencies is now off if not explicitly set. This is expected to improve the overall build time.] (rust-lang/cargo#11252) 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. - [Move `format_args!()` into AST (and expand it during AST lowering)] (rust-lang/rust#106745)

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impl DispatchFromDyn for Cell and UnsafeCell

a2d1cb2

dimpolo force-pushed the cell_dispatch_from_dyn branch from 3793feb to 1a7d8b1 Compare January 24, 2023 12:28

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add feature gate tests for DispatchFromDyn

af58854

dimpolo force-pushed the cell_dispatch_from_dyn branch from 1a7d8b1 to af58854 Compare January 24, 2023 13:23

dtolnay assigned dtolnay and unassigned m-ou-se Jan 25, 2023

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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 Jan 25, 2023

matthiaskrgr mentioned this pull request Jan 26, 2023

Rollup of 9 pull requests #107318

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bors merged commit e0d71f5 into rust-lang:master Jan 26, 2023

rustbot added this to the 1.69.0 milestone Jan 26, 2023

andersk mentioned this pull request Jan 27, 2023

Allow trait objects with methods on self: Gc<Self> on nightly Manishearth/rust-gc#162

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impl DispatchFromDyn for Cell and UnsafeCell #97373

impl DispatchFromDyn for Cell and UnsafeCell #97373

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+trait Trait2 {
+    fn cell(self: Cell<Self>); //~ ERROR invalid `self` parameter type: Cell<Self>
+}

impl DispatchFromDyn for Cell and UnsafeCell #97373

impl DispatchFromDyn for Cell and UnsafeCell #97373

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