deprecate `Eq::assert_receiver_is_total_eq` and emit FCW on manual impls by cyrgani · Pull Request #149978 · rust-lang/rust

cyrgani · 2025-12-14T09:00:21Z

The Eq::assert_receiver_is_total_eq method is purely meant as an implementation detail by #[derive(Eq)] to add checks that all fields of the type the derive is applied to also implement Eq.
The method is already #[doc(hidden)] and has a comment saying // This should never be implemented by hand..
Unfortunately, it has been stable since 1.0 and there are some cases on GitHub (https://github.com/search?q=assert_receiver_is_total_eq&type=code) where people have implemented this method manually, sometimes even with actual code in the method body (example: https://github.com/Shresht7/codecrafters-redis-rust/blob/31f0ec453c504b4ab053a7b1c3ff548ff36a9db5/src/parser/resp/types.rs#L255).
To prevent further confusion from this, this PR is deprecating the method and adds a FCW when it is manually implemented (this is necessary as the deprecation warning is not emitted when the method is implemented, only when it is called).
This is similar to what was previously done with the soft_unstable lint (#64266).

See also rust-lang/libs-team#704.

rustbot · 2025-12-14T09:00:25Z

r? @madsmtm

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compiler/rustc_lint/src/builtin.rs

madsmtm

Implementation looks good, feel free to r=me on that once you have t-libs signoff (FCP?).

Procedurally, this might also need t-lang approval for the lint name IIUC? Or can t-libs decide that?

View changes since this review

Amanieu · 2026-01-06T18:35:24Z

Since there's never a valid reason to manually implement this method, having an FCW urging people to remove their manual implementation seems like the best way to go.

@rfcbot merge libs-api lang

rust-rfcbot · 2026-01-06T18:35:26Z

Error encounted:
Provided team libs-api lang is invalid

Amanieu · 2026-01-06T18:36:47Z

@rfcbot merge

rust-rfcbot · 2026-01-06T18:36:49Z

Error encounted:
Provided team `` is invalid

Amanieu · 2026-01-06T18:37:08Z

@rfcbot merge libs-api,lang

rust-rfcbot · 2026-01-06T18:37:09Z

Team member @Amanieu 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!

cc @rust-lang/lang-advisors: FCP proposed for lang, please feel free to register concerns.
See this document for info about what commands tagged team members can give me.

rustbot · 2026-02-24T19:43:18Z

This PR was rebased onto a different main 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.

madsmtm

Looks good, thanks!

Feel free to merge with or without my nit comments.
@bors rollup delegate+

View changes since this review

compiler/rustc_lint/src/lints.rs

compiler/rustc_lint/src/builtin.rs

madsmtm · 2026-02-25T07:40:33Z

CI error is:

  error: the since field must contain a semver-compliant version
     --> library/core/src/cmp.rs:349:9
      |
  349 |         since = "CURRENT_RUSTC_VERSION",
      |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      |
      = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#deprecated_semver
      = note: `-D clippy::deprecated-semver` implied by `-D clippy::correctness`
      = help: to override `-D clippy::correctness` add `#[allow(clippy::deprecated_semver)]`

Either allow that lint, if not I'd also be fine with just naming the version that this'll get merged into.

madsmtm · 2026-02-25T07:41:00Z

Bors doesn't seem to like comments in reviews, so:
@bors delegate+ rollup

rust-bors · 2026-02-25T07:41:02Z

✌️ @cyrgani, you can now approve this pull request!

If @madsmtm told you to "r=me" after making some further change, then please make that change and post @bors r=madsmtm.

…impls

cyrgani · 2026-02-25T09:14:41Z

@bors r=madsmtm

rust-bors · 2026-02-25T09:14:44Z

📌 Commit f1ec10e has been approved by madsmtm

It is now in the queue for this repository.

…od, r=madsmtm deprecate `Eq::assert_receiver_is_total_eq` and emit FCW on manual impls The `Eq::assert_receiver_is_total_eq` method is purely meant as an implementation detail by `#[derive(Eq)]` to add checks that all fields of the type the derive is applied to also implement `Eq`. The method is already `#[doc(hidden)]` and has a comment saying `// This should never be implemented by hand.`. Unfortunately, it has been stable since 1.0 and there are some cases on GitHub (https://github.com/search?q=assert_receiver_is_total_eq&type=code) where people have implemented this method manually, sometimes even with actual code in the method body (example: https://github.com/Shresht7/codecrafters-redis-rust/blob/31f0ec453c504b4ab053a7b1c3ff548ff36a9db5/src/parser/resp/types.rs#L255). To prevent further confusion from this, this PR is deprecating the method and adds a FCW when it is manually implemented (this is necessary as the deprecation warning is not emitted when the method is implemented, only when it is called). This is similar to what was previously done with the `soft_unstable` lint (rust-lang#64266). See also rust-lang/libs-team#704.

…uwer Rollup of 13 pull requests Successful merges: - #153079 (Revert "Move aarch64-apple dist builder to dynamic llvm linking") - #148146 (CI: use alternative disks if available) - #149937 (spliit out `linker-info` from `linker-messages`) - #151771 (Fix: On wasm targets, call `panic_in_cleanup` if panic occurs in cleanup) - #153035 (rustc_target: callconv: powerpc64: Use llvm_abiname rather than target_abi for ABI determination) - #153075 (mGCA: Lower negated literals directly and reject non-integer negations) - #153078 (Remove `QuerySystemFns`) - #149978 (deprecate `Eq::assert_receiver_is_total_eq` and emit FCW on manual impls) - #153029 (Rename `rustc::pass_by_value` lint as `rustc::disallowed_pass_by_ref`.) - #153063 (`is_ty_must_use`: do not require a `span` argument) - #153071 (Update books) - #153092 (Remove redundant self usages) - #153094 (Simplify `AppendOnlyVec` iterators) Failed merges: - #153091 (Migration of `LintDiagnostic` - part 4)

Rollup of 13 pull requests Successful merges: - #148146 (CI: use alternative disks if available) - #151771 (Fix: On wasm targets, call `panic_in_cleanup` if panic occurs in cleanup) - #153035 (rustc_target: callconv: powerpc64: Use llvm_abiname rather than target_abi for ABI determination) - #153075 (mGCA: Lower negated literals directly and reject non-integer negations) - #153078 (Remove `QuerySystemFns`) - #153089 (interpret: avoid dummy spans in the stacktrace) - #153111 (Refactor url_parts to return is_absolute instead of out param) - #149978 (deprecate `Eq::assert_receiver_is_total_eq` and emit FCW on manual impls) - #153029 (Rename `rustc::pass_by_value` lint as `rustc::disallowed_pass_by_ref`.) - #153063 (`is_ty_must_use`: do not require a `span` argument) - #153071 (Update books) - #153092 (Remove redundant self usages) - #153094 (Simplify `AppendOnlyVec` iterators) Failed merges: - #153091 (Migration of `LintDiagnostic` - part 4)

Rollup merge of #149978 - cyrgani:no-eq-assert-receiver-method, r=madsmtm deprecate `Eq::assert_receiver_is_total_eq` and emit FCW on manual impls The `Eq::assert_receiver_is_total_eq` method is purely meant as an implementation detail by `#[derive(Eq)]` to add checks that all fields of the type the derive is applied to also implement `Eq`. The method is already `#[doc(hidden)]` and has a comment saying `// This should never be implemented by hand.`. Unfortunately, it has been stable since 1.0 and there are some cases on GitHub (https://github.com/search?q=assert_receiver_is_total_eq&type=code) where people have implemented this method manually, sometimes even with actual code in the method body (example: https://github.com/Shresht7/codecrafters-redis-rust/blob/31f0ec453c504b4ab053a7b1c3ff548ff36a9db5/src/parser/resp/types.rs#L255). To prevent further confusion from this, this PR is deprecating the method and adds a FCW when it is manually implemented (this is necessary as the deprecation warning is not emitted when the method is implemented, only when it is called). This is similar to what was previously done with the `soft_unstable` lint (#64266). See also rust-lang/libs-team#704.

rustbot assigned madsmtm Dec 14, 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 Dec 14, 2025

cyrgani commented Dec 14, 2025

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rust-cloud-vms bot force-pushed the no-eq-assert-receiver-method branch from faf29de to 81dc07d Compare December 14, 2025 11:30

madsmtm changed the title ~~deprecate Eq::assert_receiver_is_total_eq and emit a FCW on manual …~~ deprecate Eq::assert_receiver_is_total_eq and emit FCW on manual impls Dec 14, 2025

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cyrgani added I-lang-nominated Nominated for discussion during a lang team meeting. I-libs-nominated Nominated for discussion during a libs team meeting. labels Dec 14, 2025

rust-rfcbot added proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. disposition-merge This issue / PR is in PFCP or FCP with a disposition to merge it. labels Jan 6, 2026

Amanieu removed the I-libs-api-nominated Nominated for discussion during a libs-api team meeting. label Jan 6, 2026

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rust-cloud-vms bot force-pushed the no-eq-assert-receiver-method branch from 03140f2 to 2688fd9 Compare February 24, 2026 19:43

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madsmtm reviewed Feb 25, 2026

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deprecate Eq::assert_receiver_is_total_eq and emit a FCW on manual …

f1ec10e

…impls

rust-cloud-vms bot force-pushed the no-eq-assert-receiver-method branch from 2688fd9 to f1ec10e Compare February 25, 2026 09:13

rust-bors bot 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 25, 2026

JonathanBrouwer mentioned this pull request Feb 25, 2026

Rollup of 10 pull requests #153084

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JonathanBrouwer mentioned this pull request Feb 25, 2026

Rollup of 9 pull requests #153086

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JonathanBrouwer mentioned this pull request Feb 25, 2026

Rollup of 10 pull requests #153088

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traviscross added the relnotes Marks issues that should be documented in the release notes of the next release. label Feb 25, 2026

JonathanBrouwer mentioned this pull request Feb 25, 2026

Rollup of 13 pull requests #153098

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jhpratt mentioned this pull request Feb 26, 2026

Rollup of 13 pull requests #153116

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rust-bors bot merged commit 7a88346 into rust-lang:main Feb 26, 2026
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rustbot added this to the 1.95.0 milestone Feb 26, 2026

cyrgani deleted the no-eq-assert-receiver-method branch February 26, 2026 08:08

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