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?

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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.

…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.

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

JonathanBrouwer · 2026-02-26T21:30:49Z

@rust-timer build 74d03a9

rust-timer · 2026-02-26T22:43:37Z

Finished benchmarking commit (74d03a9): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

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

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	0.5%	[0.3%, 0.9%]	4
Regressions ❌ (secondary)	2.2%	[0.1%, 5.9%]	6
Improvements ✅ (primary)	-0.5%	[-0.5%, -0.5%]	1
Improvements ✅ (secondary)	-0.3%	[-0.3%, -0.3%]	1
All ❌✅ (primary)	0.3%	[-0.5%, 0.9%]	5

Max RSS (memory usage)

Results (primary 3.5%, secondary 4.7%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	4.9%	[2.8%, 7.5%]	5
Regressions ❌ (secondary)	4.7%	[0.8%, 8.0%]	6
Improvements ✅ (primary)	-3.8%	[-3.8%, -3.8%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	3.5%	[-3.8%, 7.5%]	6

Cycles

Results (primary -2.1%, secondary 2.0%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	4.1%	[3.6%, 4.6%]	2
Improvements ✅ (primary)	-2.1%	[-2.1%, -2.1%]	1
Improvements ✅ (secondary)	-2.3%	[-2.3%, -2.3%]	1
All ❌✅ (primary)	-2.1%	[-2.1%, -2.1%]	1

Binary size

Results (primary 0.3%, secondary 3.0%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	0.3%	[0.0%, 1.3%]	34
Regressions ❌ (secondary)	3.0%	[0.1%, 12.8%]	15
Improvements ✅ (primary)	-0.5%	[-0.5%, -0.5%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.3%	[-0.5%, 1.3%]	35

Bootstrap: 492.161s -> 479.662s (-2.54%)
Artifact size: 395.78 MiB -> 397.79 MiB (0.51%)

madsmtm · 2026-02-26T22:54:42Z

compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs

            nonself_args: vec![],
            ret_ty: Unit,
            attributes: thin_vec![
-                cx.attr_word(sym::inline, span),


Damn, I didn't think about that, but probably this that causes the regression? Inlined functions aren't codegen'd.

@cyrgani will you file a PR to fix it, or should I?

Nvmd, I filed #153157 myself

@cyrgani

…JonathanBrouwer Re-add `#[inline]` to `Eq::assert_fields_are_eq` Fixes a compile-time regression in #149978: non-inline methods are generally codegen'd while inline methods are deferred (and this function should never be called, so deferring is the right choice). r? JonathanBrouwer CC @cyrgani

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

rustbot assigned madsmtm Dec 14, 2025

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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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Rollup of 10 pull requests #153084

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Rollup of 9 pull requests #153086

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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

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Rollup of 13 pull requests #153098

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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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Re-add #[inline] to Eq::assert_fields_are_eq #153157

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Change derive macro for Eq to not impl Eq trait fn #153125

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Overall result: ❌✅ regressions and improvements - please read the text below

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