Infer all anonymous lifetimes in assoc consts as `'static` by oli-obk · Pull Request #156508 · rust-lang/rust

oli-obk · 2026-05-12T17:57:51Z

This FCW has been on for almost a year, let's actually do the change that T-lang asked for now that there's no breakage to be expected anymore. I first did a crater run checking if turning it into a hard error breaks anything.

There are two cases that would be a hard error (but totally fine by defaulting to 'static), both based on an old version of minio. One is a personal crate on github with no changes in the last year (https://github.com/PapePathe/daaray_kaamil) and the other is https://github.com/gear-tech/gear, which is developed on github actively and does not have this issue anymore (also old minio dependency that was since updated). The crates.io version is 2 years outdated.

Thus we can pretty much conclude we're not going to cause anyone any confusion or subtle bugs by changing the rules. The rules for associated constants' types are now the same as the rules for free constants' types:

We now treat all anonymous lifetimes as 'static, irrespective of whether other lifetimes are in scope or not. This means the following piece of code starts compiling without warnings or errors again.

struct Foo<'a>(&'a ());

impl<'a> Foo<'a> {
    const STR: &str = "hello, world";
}

We keep the hard error on

trait Foo {
    const B: S = S { s: &() };
}

struct S<'a> {
    s: &'a (),
}

in contrast to free constant, which are orthogonal to this change and cause more breakage

oli-obk · 2026-05-12T17:57:59Z

@bors try

Turn elided_lifetimes_in_associated_constant FCW into a hard error

rust-bors · 2026-05-12T20:07:16Z

☀️ Try build successful (CI)
Build commit: b28cc4e (b28cc4eb48a6415b914e8ad0308be255ff8d73ed, parent: 2aabf3ce0569dd7c8c2d2a27944850056dcf2566)

oli-obk · 2026-05-13T08:04:41Z

@craterbot check

craterbot · 2026-05-13T08:05:11Z

👌 Experiment pr-156508 created and queued.
🤖 Automatically detected try build b28cc4e
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

craterbot · 2026-05-21T09:59:47Z

🚧 Experiment pr-156508 is now running

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

craterbot · 2026-05-23T15:44:25Z

🎉 Experiment pr-156508 is completed!
📊 3 regressed and 10 fixed (931813 total)
📊 5201 spurious results on the retry-regressed-list.txt, consider a retry¹ if this is a significant amount.
📰 Open the summary report.

⚠️ If you notice any spurious failure please add them to the denylist!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

re-run the experiment with crates=https://crater-reports.s3.amazonaws.com/pr-156508/retry-regressed-list.txt ↩

oli-obk · 2026-05-26T09:03:05Z

@craterbot check crates=https://crater-reports.s3.amazonaws.com/pr-156508/retry-regressed-list.txt

craterbot · 2026-05-26T09:03:10Z

👌 Experiment pr-156508-1 created and queued.
🤖 Automatically detected try build b28cc4e
⚠️ Try build based on commit eaec6ce, but latest commit is a92df8e. Did you forget to make a new try build?
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

@petrochenkov

Some cleanups around passing extra lifetime params from the resolver to ast lowering No functional changes, mostly removing information that was never used at any step. Possibly interesting to @petrochenkov and @cjgillot I originally thought this was a necessary cleanup to be able to refactor our `extra_lifetime_params_map` handling, but it turns out that I can also just do rust-lang#156508 which removes all the ugly usage of that side table and makes it possible for that side table to be put into `PerOwnerResolverData`. The changes here still were an improvement on its own, thus this PR.

@petrochenkov

Some cleanups around passing extra lifetime params from the resolver to ast lowering No functional changes, mostly removing information that was never used at any step. Possibly interesting to @petrochenkov and @cjgillot I originally thought this was a necessary cleanup to be able to refactor our `extra_lifetime_params_map` handling, but it turns out that I can also just do rust-lang#156508 which removes all the ugly usage of that side table and makes it possible for that side table to be put into `PerOwnerResolverData`. The changes here still were an improvement on its own, thus this PR.

@petrochenkov

Some cleanups around passing extra lifetime params from the resolver to ast lowering No functional changes, mostly removing information that was never used at any step. Possibly interesting to @petrochenkov and @cjgillot I originally thought this was a necessary cleanup to be able to refactor our `extra_lifetime_params_map` handling, but it turns out that I can also just do rust-lang#156508 which removes all the ugly usage of that side table and makes it possible for that side table to be put into `PerOwnerResolverData`. The changes here still were an improvement on its own, thus this PR.

@petrochenkov

Rollup merge of #156960 - oli-obk:push-rrmqnqvwtmsq, r=tiif Some cleanups around passing extra lifetime params from the resolver to ast lowering No functional changes, mostly removing information that was never used at any step. Possibly interesting to @petrochenkov and @cjgillot I originally thought this was a necessary cleanup to be able to refactor our `extra_lifetime_params_map` handling, but it turns out that I can also just do #156508 which removes all the ugly usage of that side table and makes it possible for that side table to be put into `PerOwnerResolverData`. The changes here still were an improvement on its own, thus this PR.

petrochenkov · 2026-07-07T12:31:21Z

The PR description also needs an update after the last commit.
@rustbot author

rustbot · 2026-07-07T12:31:25Z

Reminder, once the PR becomes ready for a review, use @rustbot ready.

petrochenkov · 2026-07-09T11:52:12Z

-    Elided(LifetimeRes),
+    Elided {
+        res: LifetimeRes,
+        /// Always report those lifetimes as an error


It's not always an error, it's only an error if it's in a path.

View changes since the review

petrochenkov · 2026-07-09T11:52:42Z

r=me after fixing the comment and squashing commits.
@rustbot author

Hard error on hidden elided lifetimes (`S` instead of `S<'_>`) in assoc consts

rustbot · 2026-07-09T15:40:43Z

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.

oli-obk · 2026-07-09T15:43:30Z

@bors r=petrochenkov

rust-bors · 2026-07-09T15:43:33Z

📌 Commit c3257a5 has been approved by petrochenkov

It is now in the queue for this repository.

Infer all anonymous lifetimes in assoc consts as `'static` fixes rust-lang#115010 This FCW has been on for almost a year, let's actually do the change that T-lang asked for now that there's no breakage to be expected anymore. I first did a crater run checking if turning it into a hard error breaks anything. There are two cases that would be a hard error (but totally fine by defaulting to `'static`), both based on an old version of `minio`. One is a personal crate on github with no changes in the last year (https://github.com/PapePathe/daaray_kaamil) and the other is https://github.com/gear-tech/gear, which is developed on github actively and does not have this issue anymore (also old `minio` dependency that was since updated). The crates.io version is 2 years outdated. Thus we can pretty much conclude we're not going to cause anyone any confusion or subtle bugs by changing the rules. The rules for associated constants' types are now the same as the rules for free constants' types: We now treat *all* anonymous lifetimes as `'static`, irrespective of whether other lifetimes are in scope or not. This means the following piece of code starts compiling without warnings or errors again. ```rust struct Foo<'a>(&'a ()); impl<'a> Foo<'a> { const STR: &str = "hello, world"; } ``` We keep the hard error on ```rust trait Foo { const B: S = S { s: &() }; } struct S<'a> { s: &'a (), } ``` in contrast to free constant, which are orthogonal to this change and cause more breakage

…uwer Rollup of 21 pull requests Successful merges: - #150946 (intrinsics: Add a fallback for non-const libm float functions) - #158510 (Enable `static_position_independent_executables` on all gnu and musl targets) - #158541 (Move `std::io::Write` to `core::io`) - #158899 (Fix `unaligned_volatile_store` by removing `MemFlags::UNALIGNED`) - #155429 (Support `u128`/`i128` c-variadic arguments) - #156370 (Reject linked dylib EII default overrides) - #156508 (Infer all anonymous lifetimes in assoc consts as `'static`) - #158617 (allow mGCA const arguments to fall back to anon consts) - #158645 (Fix splat ICEs and ban it in closures) - #158859 (Improve `-Zls` diagnostic message on `.rs` files) - #158988 (Redo `TokenStreamIter`) - #158347 (Improve generic parameters handling for #[diagnostic::on_const]) - #158722 (delegation: do not always inherit `ConstArgHasType` predicates) - #158739 (view-types: HIR lowering) - #158883 (tests: fix enum-match.rs to handle LLVM 23) - #158886 (Add documentation for the `no_std` attribute) - #158940 (Implement feature `char_to_u32`) - #158951 (Merge three `MaxUniverse`s into one) - #158961 (Reapply "LLVM 23: Run AssignGUIDPass in some places") - #158996 ([compiler] Implement `PartialOrd` via `Ord` for `Span` and newtype_indexes) - #159005 (Use `as_lang_item` instead of repeatedly matching)

Infer all anonymous lifetimes in assoc consts as `'static` fixes rust-lang#115010 This FCW has been on for almost a year, let's actually do the change that T-lang asked for now that there's no breakage to be expected anymore. I first did a crater run checking if turning it into a hard error breaks anything. There are two cases that would be a hard error (but totally fine by defaulting to `'static`), both based on an old version of `minio`. One is a personal crate on github with no changes in the last year (https://github.com/PapePathe/daaray_kaamil) and the other is https://github.com/gear-tech/gear, which is developed on github actively and does not have this issue anymore (also old `minio` dependency that was since updated). The crates.io version is 2 years outdated. Thus we can pretty much conclude we're not going to cause anyone any confusion or subtle bugs by changing the rules. The rules for associated constants' types are now the same as the rules for free constants' types: We now treat *all* anonymous lifetimes as `'static`, irrespective of whether other lifetimes are in scope or not. This means the following piece of code starts compiling without warnings or errors again. ```rust struct Foo<'a>(&'a ()); impl<'a> Foo<'a> { const STR: &str = "hello, world"; } ``` We keep the hard error on ```rust trait Foo { const B: S = S { s: &() }; } struct S<'a> { s: &'a (), } ``` in contrast to free constant, which are orthogonal to this change and cause more breakage

…uwer Rollup of 24 pull requests Successful merges: - #150946 (intrinsics: Add a fallback for non-const libm float functions) - #158510 (Enable `static_position_independent_executables` on all gnu and musl targets) - #158541 (Move `std::io::Write` to `core::io`) - #158899 (Fix `unaligned_volatile_store` by removing `MemFlags::UNALIGNED`) - #156027 (Consider captured regions for opaque type region liveness.) - #156370 (Reject linked dylib EII default overrides) - #156508 (Infer all anonymous lifetimes in assoc consts as `'static`) - #157561 (rustdoc: do not include extra stuff in span) - #158617 (allow mGCA const arguments to fall back to anon consts) - #158645 (Fix splat ICEs and ban it in closures) - #158859 (Improve `-Zls` diagnostic message on `.rs` files) - #158988 (Redo `TokenStreamIter`) - #158347 (Improve generic parameters handling for #[diagnostic::on_const]) - #158384 (Allow BackwardIncompatibleDropHint in polonius legacy) - #158722 (delegation: do not always inherit `ConstArgHasType` predicates) - #158739 (view-types: HIR lowering) - #158877 (borrowck: Keep returned `path` from `best_blame_constraint()` consistent) - #158883 (tests: fix enum-match.rs to handle LLVM 23) - #158886 (Add documentation for the `no_std` attribute) - #158940 (Implement feature `char_to_u32`) - #158951 (Merge three `MaxUniverse`s into one) - #158961 (Reapply "LLVM 23: Run AssignGUIDPass in some places") - #158995 (Use REST API in linkchecker script) - #158996 ([compiler] Implement `PartialOrd` via `Ord` for `Span` and newtype_indexes)

Infer all anonymous lifetimes in assoc consts as `'static` fixes rust-lang#115010 This FCW has been on for almost a year, let's actually do the change that T-lang asked for now that there's no breakage to be expected anymore. I first did a crater run checking if turning it into a hard error breaks anything. There are two cases that would be a hard error (but totally fine by defaulting to `'static`), both based on an old version of `minio`. One is a personal crate on github with no changes in the last year (https://github.com/PapePathe/daaray_kaamil) and the other is https://github.com/gear-tech/gear, which is developed on github actively and does not have this issue anymore (also old `minio` dependency that was since updated). The crates.io version is 2 years outdated. Thus we can pretty much conclude we're not going to cause anyone any confusion or subtle bugs by changing the rules. The rules for associated constants' types are now the same as the rules for free constants' types: We now treat *all* anonymous lifetimes as `'static`, irrespective of whether other lifetimes are in scope or not. This means the following piece of code starts compiling without warnings or errors again. ```rust struct Foo<'a>(&'a ()); impl<'a> Foo<'a> { const STR: &str = "hello, world"; } ``` We keep the hard error on ```rust trait Foo { const B: S = S { s: &() }; } struct S<'a> { s: &'a (), } ``` in contrast to free constant, which are orthogonal to this change and cause more breakage

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels May 12, 2026