arbitrary_self_types: Split the Autoderef chain #146095

dingxiangfei2009 · 2025-09-01T16:02:27Z

Receiver chain has been an extension of Deref chain, but the consequence has been questioned as this would admit method signatures that are deemed dubious.

It is also debatable that Receiver trait which determines applicable Self type should have anything to do with dereference operation in general.

This patch separate the two traits and isolate their use in the language. This means that in method probing, we will chase down a Deref chain for an applicable type for the variable self, from which we additionally chase down a Receiver chain for an applicable Self type from a list of methods that accepts one of these possible types of self.

To facilitate discussion, we can use the Zulip thread #t-lang > Consequences of making Deref a subtrait of Receiver.

Pending items

First, gather feedback on the proposed change and assess the impact on the overall feature.
Stomp out UI test changes due to lost diagnostics, by enabling search through Receiver side-chains, so that we can suggest enabling arbitrary_self_types gate again.

rustbot · 2025-09-01T16:02:32Z

r? @jackh726

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rustbot · 2025-09-01T16:02:35Z

This PR changes a file inside tests/crashes. If a crash was fixed, please move into the corresponding ui subdir and add 'Fixes #' to the PR description to autoclose the issue upon merge.

dingxiangfei2009 · 2025-09-02T07:49:51Z

@rustbot label +F-arbitrary_self_types

Receiver chain has been an extension of Deref chain, but the consequence has been questioned as this would admit method signatures that are deemed dubious. It is also debatable that Receiver trait which determines applicable `Self` type should have anything to do with dereference operation in general. This patch separate the two traits and isolate their use in the language. This means that in method probing, we will chase down a Deref chain for an applicable type for the variable `self`, from which we additionally chase down a Receiver chain for an applicable `Self` type from a list of methods that accepts one of these possible types of `self`.

rustbot · 2025-09-02T08:44:34Z

The Miri subtree was changed

cc @rust-lang/miri

Some changes occurred in compiler/rustc_codegen_gcc

cc @antoyo, @GuillaumeGomez

rustbot · 2025-09-02T08:44:37Z

This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

rust-log-analyzer · 2025-09-02T09:16:30Z

The job aarch64-gnu-llvm-19-2 failed! Check out the build log: (web) (plain enhanced) (plain)

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

[RUSTC-TIMING] ____ test:false 0.023
##[endgroup]
##[group][AOT] arbitrary_self_types_pointers_and_wrappers
[AOT] arbitrary_self_types_pointers_and_wrappers
error[E0307]: invalid `self` parameter type: `Ptr<Wrapper<i32>>`
##[error]  --> example/arbitrary_self_types_pointers_and_wrappers.rs:41:26
   |
41 |     fn ptr_wrapper(self: Ptr<Wrapper<Self>>) -> i32 {
   |                          ^^^^^^^^^^^^^^^^^^
   |
   = note: type of `self` must be `Self` or some type implementing `Receiver`
   = help: consider changing to `self`, `&self`, `&mut self`, or a type implementing `Receiver` such as `self: Box<Self>`, `self: Rc<Self>`, or `self: Arc<Self>`

error[E0307]: invalid `self` parameter type: `Wrapper<Ptr<i32>>`
##[error]  --> example/arbitrary_self_types_pointers_and_wrappers.rs:44:26
   |
44 |     fn wrapper_ptr(self: Wrapper<Ptr<Self>>) -> i32 {
   |                          ^^^^^^^^^^^^^^^^^^
   |
   = note: type of `self` must be `Self` or some type implementing `Receiver`
   = help: consider changing to `self`, `&self`, `&mut self`, or a type implementing `Receiver` such as `self: Box<Self>`, `self: Rc<Self>`, or `self: Arc<Self>`

error[E0307]: invalid `self` parameter type: `Wrapper<Ptr<Wrapper<i32>>>`
##[error]  --> example/arbitrary_self_types_pointers_and_wrappers.rs:47:34
   |
47 |     fn wrapper_ptr_wrapper(self: Wrapper<Ptr<Wrapper<Self>>>) -> i32 {
   |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: type of `self` must be `Self` or some type implementing `Receiver`
   = help: consider changing to `self`, `&self`, `&mut self`, or a type implementing `Receiver` such as `self: Box<Self>`, `self: Rc<Self>`, or `self: Arc<Self>`

error[E0307]: invalid `self` parameter type: `Ptr<Wrapper<Self>>`
##[error]  --> example/arbitrary_self_types_pointers_and_wrappers.rs:35:26
   |
35 |     fn ptr_wrapper(self: Ptr<Wrapper<Self>>) -> i32;
   |                          ^^^^^^^^^^^^^^^^^^
   |
   = note: type of `self` must be `Self` or some type implementing `Receiver`
   = help: consider changing to `self`, `&self`, `&mut self`, or a type implementing `Receiver` such as `self: Box<Self>`, `self: Rc<Self>`, or `self: Arc<Self>`

error[E0307]: invalid `self` parameter type: `Wrapper<Ptr<Self>>`
##[error]  --> example/arbitrary_self_types_pointers_and_wrappers.rs:36:26
   |
36 |     fn wrapper_ptr(self: Wrapper<Ptr<Self>>) -> i32;
   |                          ^^^^^^^^^^^^^^^^^^
   |
   = note: type of `self` must be `Self` or some type implementing `Receiver`
   = help: consider changing to `self`, `&self`, `&mut self`, or a type implementing `Receiver` such as `self: Box<Self>`, `self: Rc<Self>`, or `self: Arc<Self>`

error[E0307]: invalid `self` parameter type: `Wrapper<Ptr<Wrapper<Self>>>`
##[error]  --> example/arbitrary_self_types_pointers_and_wrappers.rs:37:34
   |
37 |     fn wrapper_ptr_wrapper(self: Wrapper<Ptr<Wrapper<Self>>>) -> i32;
   |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: type of `self` must be `Self` or some type implementing `Receiver`
   = help: consider changing to `self`, `&self`, `&mut self`, or a type implementing `Receiver` such as `self: Box<Self>`, `self: Rc<Self>`, or `self: Arc<Self>`

error: aborting due to 6 previous errors

For more information about this error, try `rustc --explain E0307`.
"/checkout/obj/build/aarch64-unknown-linux-gnu/stage2-codegen/cg_clif/dist/rustc-clif" "-Csymbol-mangling-version=v0" "-Zrandomize-layout" "-Zunstable-options" "--check-cfg=cfg(bootstrap)" "--check-cfg=cfg(llvm_enzyme)" "-Zmacro-backtrace" "-Csplit-debuginfo=off" "-Clink-arg=-L/usr/lib/llvm-19/lib" "-Cllvm-args=-import-instr-limit=10" "-Clink-args=-Wl,-z,origin" "-Clink-args=-Wl,-rpath,$ORIGIN/../lib" "-Alinker-messages" "-L" "crate=/checkout/obj/build/aarch64-unknown-linux-gnu/stage2-codegen/cg_clif/build/example" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2-codegen/cg_clif/build/example" "-Cdebuginfo=2" "--target" "aarch64-unknown-linux-gnu" "-Cpanic=abort" "--check-cfg=cfg(jit)" "example/arbitrary_self_types_pointers_and_wrappers.rs" exited with status ExitStatus(unix_wait_status(256))
Command `/checkout/obj/build/aarch64-unknown-linux-gnu/stage0/bin/cargo run --target aarch64-unknown-linux-gnu -Zbinary-dep-depinfo -j 4 -Zroot-dir=/checkout --locked --color always --release --manifest-path /checkout/compiler/rustc_codegen_cranelift/build_system/Cargo.toml -- test --download-dir /checkout/obj/build/cg_clif_download --out-dir /checkout/obj/build/aarch64-unknown-linux-gnu/stage2-codegen/cg_clif --no-unstable-features --use-backend cranelift --sysroot llvm --skip-test testsuite.extended_sysroot [workdir=/checkout/compiler/rustc_codegen_cranelift]` failed with exit code 1
Created at: src/bootstrap/src/core/build_steps/test.rs:3645:25
Executed at: src/bootstrap/src/core/build_steps/test.rs:3686:26

Command has failed. Rerun with -v to see more details.
Bootstrap failed while executing `--stage 2 test --skip tests --skip coverage-map --skip coverage-run --skip library --skip tidyselftest`
Build completed unsuccessfully in 0:25:15
  local time: Tue Sep  2 09:16:17 UTC 2025
  network time: Tue, 02 Sep 2025 09:16:17 GMT
##[error]Process completed with exit code 1.

jackh726 · 2025-09-03T17:02:42Z

Is this waiting on discussion and a decision from the lang team?

dingxiangfei2009 · 2025-09-04T11:11:37Z

@jackh726 Sorry I was not very clear. Indeed it would need a lang team discussion.

To support the discussion, I am writing a report to describe what changes this would bring to the feature.

cc @traviscross @tmandry

rustbot assigned jackh726 Sep 1, 2025

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. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Sep 1, 2025

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dingxiangfei2009 force-pushed the autoderef-split branch from bef5ba5 to f3e8785 Compare September 1, 2025 20:14

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dingxiangfei2009 force-pushed the autoderef-split branch from f3e8785 to 31788b7 Compare September 1, 2025 20:38

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rustbot added the F-arbitrary_self_types `#![feature(arbitrary_self_types)]` label Sep 2, 2025

dingxiangfei2009 force-pushed the autoderef-split branch from 31788b7 to 1a2dbf8 Compare September 2, 2025 08:44

ojeda mentioned this pull request Aug 31, 2025

Rust unstable features needed for the kernel Rust-for-Linux/linux#2

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