Remove dead code and extend test coverage and diagnostics around it #144390

oli-obk · 2025-07-24T10:03:24Z

I was staring a bit at the dont_niche_optimize_enum variable and figured out that part of it is dead code (at least today it is). I changed the diagnostic and test around the code that makes that part dead code, so everything that makes removing that code sound is visible in this PR

rustbot · 2025-07-24T10:03:29Z

r? @SparrowLii

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oli-obk · 2025-07-24T10:03:40Z

compiler/rustc_ty_utils/src/layout.rs

-                || def
-                    .variants()
-                    .iter_enumerated()
-                    .any(|(i, v)| v.discr != ty::VariantDiscr::Relative(i.as_u32()));


We lost the following comment during refactorings in the past:

The current code for niche-filling relies on variant indices instead of actual discriminants, so enums with explicit discriminants (RFC #2363) would misbehave.

But inhibit_enum_layout_opt is true for any type with a repr(some_int) attribute, and that attribute is required for any type where niche optimizations could happen (so enums with non-unit variants)

Sounds reasonable

We lost the following comment during refactorings: The current code for niche-filling relies on variant indices instead of actual discriminants, so enums with explicit discriminants (RFC 2363) would misbehave.

rustbot · 2025-07-24T10:21:30Z

rust-analyzer is developed in its own repository. If possible, consider making this change to rust-lang/rust-analyzer instead.

cc @rust-lang/rust-analyzer

oli-obk · 2025-07-24T10:21:47Z

Ah fun, r-a preserved the comment 😆

SparrowLii · 2025-07-24T11:23:51Z

Should we get approved from r-a's people first?
r=me if it's all right

oli-obk · 2025-07-24T13:08:39Z

I'll treat @Veykril 's laughing emoji as approval 😆

@bors r=SparrowLii

bors · 2025-07-24T13:08:42Z

📌 Commit e44a738 has been approved by SparrowLii

It is now in the queue for this repository.

…parrowLii Remove dead code and extend test coverage and diagnostics around it I was staring a bit at the `dont_niche_optimize_enum` variable and figured out that part of it is dead code (at least today it is). I changed the diagnostic and test around the code that makes that part dead code, so everything that makes removing that code sound is visible in this PR

Rollup of 16 pull requests Successful merges: - #142569 (Suggest clone in user-write-code instead of inside macro) - #143401 (tests: Don't check for self-printed output in std-backtrace.rs test) - #143424 (clippy fix: rely on autoderef) - #143970 (Update core::mem::copy documentation) - #143979 (Test fixes for Arm64EC Windows) - #144160 (tests: debuginfo: Work around or disable broken tests on powerpc) - #144200 (Tweak output for non-`Clone` values moved into closures) - #144209 (Don't emit two `assume`s in transmutes when one is a subset of the other) - #144225 (Don't special-case llvm.* as nounwind) - #144314 (Hint that choose_pivot returns index in bounds) - #144316 (bootstrap: Move musl-root fallback out of sanity check) - #144364 (Update `dlmalloc` dependency of libstd) - #144368 (resolve: Remove `Scope::CrateRoot`) - #144373 (remove deprecated Error::description in impls) - #144390 (Remove dead code and extend test coverage and diagnostics around it) - #144392 (rustc_public: Remove movability from `RigidTy/AggregateKind::Coroutine`) r? `@ghost` `@rustbot` modify labels: rollup

…parrowLii Remove dead code and extend test coverage and diagnostics around it I was staring a bit at the `dont_niche_optimize_enum` variable and figured out that part of it is dead code (at least today it is). I changed the diagnostic and test around the code that makes that part dead code, so everything that makes removing that code sound is visible in this PR

Rollup of 17 pull requests Successful merges: - #142569 (Suggest clone in user-write-code instead of inside macro) - #143401 (tests: Don't check for self-printed output in std-backtrace.rs test) - #143424 (clippy fix: rely on autoderef) - #143970 (Update core::mem::copy documentation) - #143979 (Test fixes for Arm64EC Windows) - #144160 (tests: debuginfo: Work around or disable broken tests on powerpc) - #144200 (Tweak output for non-`Clone` values moved into closures) - #144209 (Don't emit two `assume`s in transmutes when one is a subset of the other) - #144225 (Don't special-case llvm.* as nounwind) - #144314 (Hint that choose_pivot returns index in bounds) - #144316 (bootstrap: Move musl-root fallback out of sanity check) - #144340 (UI test suite clarity changes: Rename `tests/ui/SUMMARY.md` and update rustc dev guide on `error-pattern`) - #144364 (Update `dlmalloc` dependency of libstd) - #144368 (resolve: Remove `Scope::CrateRoot`) - #144390 (Remove dead code and extend test coverage and diagnostics around it) - #144392 (rustc_public: Remove movability from `RigidTy/AggregateKind::Coroutine`) - #144424 (Allow setting `release-blog-post` label with rustbot) r? `@ghost` `@rustbot` modify labels: rollup

…parrowLii Remove dead code and extend test coverage and diagnostics around it I was staring a bit at the `dont_niche_optimize_enum` variable and figured out that part of it is dead code (at least today it is). I changed the diagnostic and test around the code that makes that part dead code, so everything that makes removing that code sound is visible in this PR

Rollup of 16 pull requests Successful merges: - #142569 (Suggest clone in user-write-code instead of inside macro) - #143401 (tests: Don't check for self-printed output in std-backtrace.rs test) - #143424 (clippy fix: rely on autoderef) - #143970 (Update core::mem::copy documentation) - #143979 (Test fixes for Arm64EC Windows) - #144160 (tests: debuginfo: Work around or disable broken tests on powerpc) - #144200 (Tweak output for non-`Clone` values moved into closures) - #144209 (Don't emit two `assume`s in transmutes when one is a subset of the other) - #144314 (Hint that choose_pivot returns index in bounds) - #144316 (bootstrap: Move musl-root fallback out of sanity check) - #144340 (UI test suite clarity changes: Rename `tests/ui/SUMMARY.md` and update rustc dev guide on `error-pattern`) - #144364 (Update `dlmalloc` dependency of libstd) - #144368 (resolve: Remove `Scope::CrateRoot`) - #144390 (Remove dead code and extend test coverage and diagnostics around it) - #144392 (rustc_public: Remove movability from `RigidTy/AggregateKind::Coroutine`) - #144424 (Allow setting `release-blog-post` label with rustbot) r? `@ghost` `@rustbot` modify labels: rollup

Rollup of 12 pull requests Successful merges: - #142569 (Suggest clone in user-write-code instead of inside macro) - #143401 (tests: Don't check for self-printed output in std-backtrace.rs test) - #143424 (clippy fix: rely on autoderef) - #143970 (Update core::mem::copy documentation) - #143979 (Test fixes for Arm64EC Windows) - #144200 (Tweak output for non-`Clone` values moved into closures) - #144209 (Don't emit two `assume`s in transmutes when one is a subset of the other) - #144314 (Hint that choose_pivot returns index in bounds) - #144340 (UI test suite clarity changes: Rename `tests/ui/SUMMARY.md` and update rustc dev guide on `error-pattern`) - #144368 (resolve: Remove `Scope::CrateRoot`) - #144390 (Remove dead code and extend test coverage and diagnostics around it) - #144392 (rustc_public: Remove movability from `RigidTy/AggregateKind::Coroutine`) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of #144390 - oli-obk:arbitrary-enum-discrs, r=SparrowLii Remove dead code and extend test coverage and diagnostics around it I was staring a bit at the `dont_niche_optimize_enum` variable and figured out that part of it is dead code (at least today it is). I changed the diagnostic and test around the code that makes that part dead code, so everything that makes removing that code sound is visible in this PR

Rollup of 12 pull requests Successful merges: - rust-lang/rust#142569 (Suggest clone in user-write-code instead of inside macro) - rust-lang/rust#143401 (tests: Don't check for self-printed output in std-backtrace.rs test) - rust-lang/rust#143424 (clippy fix: rely on autoderef) - rust-lang/rust#143970 (Update core::mem::copy documentation) - rust-lang/rust#143979 (Test fixes for Arm64EC Windows) - rust-lang/rust#144200 (Tweak output for non-`Clone` values moved into closures) - rust-lang/rust#144209 (Don't emit two `assume`s in transmutes when one is a subset of the other) - rust-lang/rust#144314 (Hint that choose_pivot returns index in bounds) - rust-lang/rust#144340 (UI test suite clarity changes: Rename `tests/ui/SUMMARY.md` and update rustc dev guide on `error-pattern`) - rust-lang/rust#144368 (resolve: Remove `Scope::CrateRoot`) - rust-lang/rust#144390 (Remove dead code and extend test coverage and diagnostics around it) - rust-lang/rust#144392 (rustc_public: Remove movability from `RigidTy/AggregateKind::Coroutine`) r? `@ghost` `@rustbot` modify labels: rollup

rustbot assigned SparrowLii Jul 24, 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. labels Jul 24, 2025

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oli-obk commented Jul 24, 2025

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oli-obk force-pushed the arbitrary-enum-discrs branch from d6a149d to b9c22f5 Compare July 24, 2025 10:05

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Remove dead code and extend test coverage and diagnostics around it

e44a738

We lost the following comment during refactorings: The current code for niche-filling relies on variant indices instead of actual discriminants, so enums with explicit discriminants (RFC 2363) would misbehave.

oli-obk force-pushed the arbitrary-enum-discrs branch from b9c22f5 to e44a738 Compare July 24, 2025 10:21

SparrowLii approved these changes Jul 24, 2025

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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 Jul 24, 2025

fmease mentioned this pull request Jul 24, 2025

Rollup of 16 pull requests #144418

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fmease mentioned this pull request Jul 25, 2025

Rollup of 17 pull requests #144428

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This was referenced Jul 25, 2025

Rollup of 16 pull requests #144436

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Rollup of 12 pull requests #144440

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bors merged commit acd4a1c into rust-lang:master Jul 25, 2025
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