don't ice on non-lifetime binders under `-Zassumptions-on-binders` by Dnreikronos · Pull Request #157807 · rust-lang/rust

Dnreikronos · 2026-06-12T11:51:00Z

w/ -Znext-solver=globally -Zassumptions-on-binders and a non-lifetime binder we hit assert!(max_universe < u) in pull_region_outlives_constraints_out_of_universe and ICE.

the machinery here is region-outlives only, but a for<T> binder leaves a placeholder type in universe u that the region-only rewrite can't pull out, so an alias outlives like <!T as Trait>::Assoc: 'r reaches that assert still in u. just report ambiguity in that case, same as the None => Ambiguity bails right next to it — now it errors normally (E0284) instead of ICEing.

r? @lcnr

The region-constraint machinery for `-Zassumptions-on-binders` is region-outlives-only. A non-lifetime binder (`for<T>`) introduces a placeholder type in the binder's universe `u`. The rewrite that pulls constraints out of `u` only folds regions (`PlaceholderReplacer` just implements `fold_region`), so an alias-outlives constraint such as `<!T as Trait>::Assoc: 'r` reaches `pull_region_outlives_constraints_out_of_universe` still in `u` and trips `assert!(max_universe < u)`. Report ambiguity for those constraints instead of asserting, matching the existing `None => Ambiguity` bail-outs in this module. The goal then surfaces as an ordinary ambiguity error rather than an ICE.

lcnr · 2026-06-12T12:15:18Z

r? BoxyUwU

BoxyUwU · 2026-06-19T13:59:29Z

can you move this logic into rewrite_type_outlives_constraints_in_universe_for_eager_placeholder_handling 🤔 it feels surprising that pull_region_outlives_constraints would do anything to type outlives constraints and similarly that rewrite_type_outlives_constraints wouldn't fully handle type outlives' :3

Dnreikronos · 2026-06-19T20:26:32Z

done, moved this into rewrite_type_outlives_constraints_in_universe_for_eager_placeholder_handling.

pull_region_outlives_constraints_out_of_universe is back to just asserting that any ty-outlives constraint it sees was already moved below u. the alias rewrite handles the leftover non-lifetime placeholder case now, and turns it into ambiguity before the region-only pass runs.

idk if this is the exact shape you had in mind, but lgtm locally. imp bit is that pull_region_outlives_constraints_out_of_universe doesn't decide ty-outlives stuff anymore.

BoxyUwU · 2026-06-23T09:54:33Z

@bors r+ rollup

rust-bors · 2026-06-23T09:54:37Z

📌 Commit a2f80c9 has been approved by BoxyUwU

It is now in the queue for this repository.

@lcnr

…_non_lifetime_binder_ambiguity, r=BoxyUwU don't ice on non-lifetime binders under `-Zassumptions-on-binders` fixes rust-lang#157778 w/ `-Znext-solver=globally -Zassumptions-on-binders` and a non-lifetime binder we hit `assert!(max_universe < u)` in `pull_region_outlives_constraints_out_of_universe` and ICE. the machinery here is region-outlives only, but a `for<T>` binder leaves a placeholder type in universe `u` that the region-only rewrite can't pull out, so an alias outlives like `<!T as Trait>::Assoc: 'r` reaches that assert still in `u`. just report ambiguity in that case, same as the `None => Ambiguity` bails right next to it — now it errors normally (E0284) instead of ICEing. r? @lcnr

…uwer Rollup of 16 pull requests Successful merges: - #156885 (Fix misattributed type inference error span for index expressions) - #157271 (simplify some `proc_macro` things) - #157883 (Remove strict invariant node_type on hir_type during ty privacy visit) - #157921 (trait solver: Resolve region vars in max universe) - #157960 (delegation: add support for infers in generics) - #158105 (Extract all instance shim variants into new `ShimKind` enum) - #158207 (Resolver: local/external split of `resolve_ident_in_module_non_globs_unadjusted` ) - #158279 (Follow goto and drop when linting unreachable code) - #157807 (don't ice on non-lifetime binders under `-Zassumptions-on-binders`) - #158020 (Update mingw-w64 C toolchain) - #158222 (format: ignore println newline in foreign format hints) - #158223 (Move target checking for #[lang] to the attribute parser) - #158252 (Use `cfg_select` in `std::os`) - #158257 ( fix escaping placeholder check in next solver normalization folder) - #158274 (triagebot: Stop pinging myself) - #158282 (slice_split_once: bounds check optimization note) Failed merges: - #158256 (Avoid parser panics bubbling out to proc macros)

@lcnr

…_non_lifetime_binder_ambiguity, r=BoxyUwU don't ice on non-lifetime binders under `-Zassumptions-on-binders` fixes rust-lang#157778 w/ `-Znext-solver=globally -Zassumptions-on-binders` and a non-lifetime binder we hit `assert!(max_universe < u)` in `pull_region_outlives_constraints_out_of_universe` and ICE. the machinery here is region-outlives only, but a `for<T>` binder leaves a placeholder type in universe `u` that the region-only rewrite can't pull out, so an alias outlives like `<!T as Trait>::Assoc: 'r` reaches that assert still in `u`. just report ambiguity in that case, same as the `None => Ambiguity` bails right next to it — now it errors normally (E0284) instead of ICEing. r? @lcnr

@lcnr

…_non_lifetime_binder_ambiguity, r=BoxyUwU don't ice on non-lifetime binders under `-Zassumptions-on-binders` fixes rust-lang#157778 w/ `-Znext-solver=globally -Zassumptions-on-binders` and a non-lifetime binder we hit `assert!(max_universe < u)` in `pull_region_outlives_constraints_out_of_universe` and ICE. the machinery here is region-outlives only, but a `for<T>` binder leaves a placeholder type in universe `u` that the region-only rewrite can't pull out, so an alias outlives like `<!T as Trait>::Assoc: 'r` reaches that assert still in `u`. just report ambiguity in that case, same as the `None => Ambiguity` bails right next to it — now it errors normally (E0284) instead of ICEing. r? @lcnr

…uwer Rollup of 23 pull requests Successful merges: - #158315 (`rust-analyzer` subtree update) - #155739 (Add temporary scope to assert_eq and assert_ne) - #156885 (Fix misattributed type inference error span for index expressions) - #157271 (simplify some `proc_macro` things) - #157883 (Remove strict invariant node_type on hir_type during ty privacy visit) - #157921 (trait solver: Resolve region vars in max universe) - #157960 (delegation: add support for infers in generics) - #157983 (Lift the same-signature restriction for `extern "tail"`) - #158105 (Extract all instance shim variants into new `ShimKind` enum) - #158207 (Resolver: local/external split of `resolve_ident_in_module_non_globs_unadjusted` ) - #158279 (Follow goto and drop when linting unreachable code) - #157527 (Move derive tests into their dedicated folder) - #157807 (don't ice on non-lifetime binders under `-Zassumptions-on-binders`) - #158020 (Update mingw-w64 C toolchain) - #158222 (format: ignore println newline in foreign format hints) - #158223 (Move target checking for #[lang] to the attribute parser) - #158252 (Use `cfg_select` in `std::os`) - #158257 ( fix escaping placeholder check in next solver normalization folder) - #158263 (Only load the feature list once in the entire resolver) - #158274 (triagebot: Stop pinging myself) - #158282 (slice_split_once: bounds check optimization note) - #158300 (Improve unknown crate_type diagnostic suggestions) - #158304 (mailmap: update mu001999) Failed merges: - #158256 (Avoid parser panics bubbling out to proc macros)

@lcnr

…_non_lifetime_binder_ambiguity, r=BoxyUwU don't ice on non-lifetime binders under `-Zassumptions-on-binders` fixes rust-lang#157778 w/ `-Znext-solver=globally -Zassumptions-on-binders` and a non-lifetime binder we hit `assert!(max_universe < u)` in `pull_region_outlives_constraints_out_of_universe` and ICE. the machinery here is region-outlives only, but a `for<T>` binder leaves a placeholder type in universe `u` that the region-only rewrite can't pull out, so an alias outlives like `<!T as Trait>::Assoc: 'r` reaches that assert still in `u`. just report ambiguity in that case, same as the `None => Ambiguity` bails right next to it — now it errors normally (E0284) instead of ICEing. r? @lcnr

Rollup of 27 pull requests Successful merges: - #158315 (`rust-analyzer` subtree update) - #155739 (Add temporary scope to assert_eq and assert_ne) - #156885 (Fix misattributed type inference error span for index expressions) - #157271 (simplify some `proc_macro` things) - #157883 (Remove strict invariant node_type on hir_type during ty privacy visit) - #157921 (trait solver: Resolve region vars in max universe) - #157960 (delegation: add support for infers in generics) - #157983 (Lift the same-signature restriction for `extern "tail"`) - #158053 (Optimize network address parser) - #158105 (Extract all instance shim variants into new `ShimKind` enum) - #158207 (Resolver: local/external split of `resolve_ident_in_module_non_globs_unadjusted` ) - #158279 (Follow goto and drop when linting unreachable code) - #157527 (Move derive tests into their dedicated folder) - #157807 (don't ice on non-lifetime binders under `-Zassumptions-on-binders`) - #158020 (Update mingw-w64 C toolchain) - #158039 (c-variadic: test that we use equality up to free lifetimes) - #158222 (format: ignore println newline in foreign format hints) - #158223 (Move target checking for #[lang] to the attribute parser) - #158252 (Use `cfg_select` in `std::os`) - #158257 ( fix escaping placeholder check in next solver normalization folder) - #158263 (Only load the feature list once in the entire resolver) - #158267 (FromUtf8Error::into_utf8_lossy better example and suggest use) - #158274 (triagebot: Stop pinging myself) - #158282 (slice_split_once: bounds check optimization note) - #158300 (Improve unknown crate_type diagnostic suggestions) - #158304 (mailmap: update mu001999) - #158309 (Update `rustc-literal-escaper` version to `0.0.8`) Failed merges: - #158256 (Avoid parser panics bubbling out to proc macros)

@lcnr

…_non_lifetime_binder_ambiguity, r=BoxyUwU don't ice on non-lifetime binders under `-Zassumptions-on-binders` fixes rust-lang#157778 w/ `-Znext-solver=globally -Zassumptions-on-binders` and a non-lifetime binder we hit `assert!(max_universe < u)` in `pull_region_outlives_constraints_out_of_universe` and ICE. the machinery here is region-outlives only, but a `for<T>` binder leaves a placeholder type in universe `u` that the region-only rewrite can't pull out, so an alias outlives like `<!T as Trait>::Assoc: 'r` reaches that assert still in `u`. just report ambiguity in that case, same as the `None => Ambiguity` bails right next to it — now it errors normally (E0284) instead of ICEing. r? @lcnr

Rollup of 35 pull requests Successful merges: - #158315 (`rust-analyzer` subtree update) - #158336 (Stop excluding `stdarch` test crates from `rust-src`) - #155739 (Add temporary scope to assert_eq and assert_ne) - #156885 (Fix misattributed type inference error span for index expressions) - #157271 (simplify some `proc_macro` things) - #157419 (move rustc_type_ir Term things to term_kind.rs) - #157883 (Remove strict invariant node_type on hir_type during ty privacy visit) - #157921 (trait solver: Resolve region vars in max universe) - #157960 (delegation: add support for infers in generics) - #157983 (Lift the same-signature restriction for `extern "tail"`) - #158053 (Optimize network address parser) - #158105 (Extract all instance shim variants into new `ShimKind` enum) - #158207 (Resolver: local/external split of `resolve_ident_in_module_non_globs_unadjusted` ) - #158279 (Follow goto and drop when linting unreachable code) - #157527 (Move derive tests into their dedicated folder) - #157807 (don't ice on non-lifetime binders under `-Zassumptions-on-binders`) - #157939 (Reorganize `tests/ui/issues` [8/N]) - #157946 (Make `char::is_private_use` and `char::is_assigned` unstably public) - #158003 (Reorganize `tests/ui/issues` [9/N]) - #158020 (Update mingw-w64 C toolchain) - #158039 (c-variadic: test that we use equality up to free lifetimes) - #158060 (Reorganize `tests/ui/issues` [10/N]) - #158222 (format: ignore println newline in foreign format hints) - #158223 (Move target checking for #[lang] to the attribute parser) - #158252 (Use `cfg_select` in `std::os`) - #158263 (Only load the feature list once in the entire resolver) - #158267 (FromUtf8Error::into_utf8_lossy better example and suggest use) - #158272 (Reorganize `tests/ui/issues` [13/N]) - #158274 (triagebot: Stop pinging myself) - #158282 (slice_split_once: bounds check optimization note) - #158300 (Improve unknown crate_type diagnostic suggestions) - #158304 (mailmap: update mu001999) - #158309 (Update `rustc-literal-escaper` version to `0.0.8`) - #158314 (Fix incorrect unsafe debug assertion in unchecked_div_exact) - #158326 (Add `io::ErrorKind::TooManyOpenFiles`)

@lcnr

…_non_lifetime_binder_ambiguity, r=BoxyUwU don't ice on non-lifetime binders under `-Zassumptions-on-binders` fixes rust-lang#157778 w/ `-Znext-solver=globally -Zassumptions-on-binders` and a non-lifetime binder we hit `assert!(max_universe < u)` in `pull_region_outlives_constraints_out_of_universe` and ICE. the machinery here is region-outlives only, but a `for<T>` binder leaves a placeholder type in universe `u` that the region-only rewrite can't pull out, so an alias outlives like `<!T as Trait>::Assoc: 'r` reaches that assert still in `u`. just report ambiguity in that case, same as the `None => Ambiguity` bails right next to it — now it errors normally (E0284) instead of ICEing. r? @lcnr

Rollup of 35 pull requests Successful merges: - #158315 (`rust-analyzer` subtree update) - #158336 (Stop excluding `stdarch` test crates from `rust-src`) - #155739 (Add temporary scope to assert_eq and assert_ne) - #156885 (Fix misattributed type inference error span for index expressions) - #157271 (simplify some `proc_macro` things) - #157419 (move rustc_type_ir Term things to term_kind.rs) - #157883 (Remove strict invariant node_type on hir_type during ty privacy visit) - #157921 (trait solver: Resolve region vars in max universe) - #157960 (delegation: add support for infers in generics) - #157983 (Lift the same-signature restriction for `extern "tail"`) - #158053 (Optimize network address parser) - #158105 (Extract all instance shim variants into new `ShimKind` enum) - #158207 (Resolver: local/external split of `resolve_ident_in_module_non_globs_unadjusted` ) - #158279 (Follow goto and drop when linting unreachable code) - #157527 (Move derive tests into their dedicated folder) - #157807 (don't ice on non-lifetime binders under `-Zassumptions-on-binders`) - #157939 (Reorganize `tests/ui/issues` [8/N]) - #157946 (Make `char::is_private_use` and `char::is_assigned` unstably public) - #158003 (Reorganize `tests/ui/issues` [9/N]) - #158020 (Update mingw-w64 C toolchain) - #158039 (c-variadic: test that we use equality up to free lifetimes) - #158060 (Reorganize `tests/ui/issues` [10/N]) - #158222 (format: ignore println newline in foreign format hints) - #158223 (Move target checking for #[lang] to the attribute parser) - #158252 (Use `cfg_select` in `std::os`) - #158263 (Only load the feature list once in the entire resolver) - #158267 (FromUtf8Error::into_utf8_lossy better example and suggest use) - #158272 (Reorganize `tests/ui/issues` [13/N]) - #158274 (triagebot: Stop pinging myself) - #158282 (slice_split_once: bounds check optimization note) - #158300 (Improve unknown crate_type diagnostic suggestions) - #158304 (mailmap: update mu001999) - #158309 (Update `rustc-literal-escaper` version to `0.0.8`) - #158314 (Fix incorrect unsafe debug assertion in unchecked_div_exact) - #158326 (Add `io::ErrorKind::TooManyOpenFiles`)

@lcnr

Rollup merge of #157807 - Dnreikronos:assumptions_on_binders_non_lifetime_binder_ambiguity, r=BoxyUwU don't ice on non-lifetime binders under `-Zassumptions-on-binders` fixes #157778 w/ `-Znext-solver=globally -Zassumptions-on-binders` and a non-lifetime binder we hit `assert!(max_universe < u)` in `pull_region_outlives_constraints_out_of_universe` and ICE. the machinery here is region-outlives only, but a `for<T>` binder leaves a placeholder type in universe `u` that the region-only rewrite can't pull out, so an alias outlives like `<!T as Trait>::Assoc: 'r` reaches that assert still in `u`. just report ambiguity in that case, same as the `None => Ambiguity` bails right next to it — now it errors normally (E0284) instead of ICEing. r? @lcnr

rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jun 12, 2026

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rustbot added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Jun 12, 2026

rustbot assigned BoxyUwU and unassigned lcnr Jun 12, 2026

Handle alias outlives ambiguity during rewrite

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don't ice on non-lifetime binders under `-Zassumptions-on-binders`#157807

don't ice on non-lifetime binders under `-Zassumptions-on-binders`#157807
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Dnreikronos:assumptions_on_binders_non_lifetime_binder_ambiguity

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