only make `RustaceansAreAwesome` satisfy trait clauses by dianne · Pull Request #163958 · rust-lang/rust

dianne · 2026-10-07T22:48:39Z

Fixes #163550 but unfortunately partially un-fixes a variant of #161621 that hadn't been reported. I have a followup to re-fix that, but I ended up deciding that it would probably be easier to review separately; I'll open a PR for that later.

The variant in question:

trait HasAssoc {
    type Assoc;
}

trait Parent<T> {}

trait Trait
where
    (Self,): HasAssoc<Assoc = str>,
    Self: Parent<<<(Self,) as HasAssoc>::Assoc as ToOwned>::Owned>,
{
    fn f(&self);
    //~^ ERROR: the trait bound `<(RustaceansAreAwesome,) as HasAssoc>::Assoc: Clone` is not satisfied
    //~| NOTE: required for `<(RustaceansAreAwesome,) as HasAssoc>::Assoc` to implement `ToOwned`
}

This fails to prove <(RustaceansAreAwesome,) as HasAssoc>::Assoc: Owned because it can't normalize that alias to str. The followup will re-add projections as necessary for this in a hopefully-non-breaking way.

dianne · 2026-10-07T22:50:05Z

+//! Tests for specific instances of <https://github.com/rust-lang/rust/issues/161621> that don't
+//! pass yet. See `dispatchability-placeholder-satisfies-bounds.rs` for context.
+// FIXME(@dianne): this should be gone soon
+//@ known-bug: unknown


I've left this as unknown for now since the issue is currently marked as closed and this issue is significantly more specific than what was reported there. not sure if it should be reopened until the followup to this lands or a new issue is warranted

View changes since the review

since you're following up immediately, this is fine

dianne · 2026-10-07T22:52:55Z

I've dumped all the passing tests in this file since they share a significant amount of context, especially when adding in the tests I've written for the followup to this, where many tests build on concepts that were set up in previous tests. maybe some of them should be split apart though?

View changes since the review

Seems fine this way. A little bit more annoying to debug when only one of them breaks, but they are all very related

dianne · 2026-10-08T00:08:05Z

this is a fix for #163200, so r? @oli-obk or reassign

oli-obk

@bors r+ rollup

View changes since this review

rust-bors · 2026-10-08T10:23:55Z

📌 Commit df42c7b has been approved by oli-obk

It is now in the queue for this repository.

…ke-2-partial, r=oli-obk only make `RustaceansAreAwesome` satisfy trait clauses Fixes rust-lang#163550 but unfortunately partially un-fixes a variant of rust-lang#161621 that hadn't been reported. I have a followup to re-fix that, but I ended up deciding that it would probably be easier to review separately; I'll open a PR for that later. The variant in question: ```rust trait HasAssoc { type Assoc; } trait Parent<T> {} trait Trait where (Self,): HasAssoc<Assoc = str>, Self: Parent<<<(Self,) as HasAssoc>::Assoc as ToOwned>::Owned>, { fn f(&self); //~^ ERROR: the trait bound `<(RustaceansAreAwesome,) as HasAssoc>::Assoc: Clone` is not satisfied //~| NOTE: required for `<(RustaceansAreAwesome,) as HasAssoc>::Assoc` to implement `ToOwned` } ``` This fails to prove `<(RustaceansAreAwesome,) as HasAssoc>::Assoc: Owned` because it can't normalize that alias to `str`. The followup will re-add projections as necessary for this in a hopefully-non-breaking way.

…uwer Rollup of 9 pull requests Successful merges: - #163462 (Fix COFF renaming of decorated (stdcall/fastcall/vectorcall) exports) - #163855 (Include enclosing item's context on const errors) - #163861 (Run LLDB debuginfo tests on `x86_64-mingw`) - #163538 (Add `rustc::missing_generic_type_visitable` lint) - #163617 (mips: make `Complex<T>` ABI match GCC) - #163832 (reject non-async coroutine closures as async callables) - #163958 (only make `RustaceansAreAwesome` satisfy trait clauses) - #163974 (Condense AdtDef lang item checks into one match) - #163979 (Add `bf16` to arm features) Failed merges: - #163972 (const-eval: ICE when we hit a non-const fn)

…ke-2-partial, r=oli-obk only make `RustaceansAreAwesome` satisfy trait clauses Fixes rust-lang#163550 but unfortunately partially un-fixes a variant of rust-lang#161621 that hadn't been reported. I have a followup to re-fix that, but I ended up deciding that it would probably be easier to review separately; I'll open a PR for that later. The variant in question: ```rust trait HasAssoc { type Assoc; } trait Parent<T> {} trait Trait where (Self,): HasAssoc<Assoc = str>, Self: Parent<<<(Self,) as HasAssoc>::Assoc as ToOwned>::Owned>, { fn f(&self); //~^ ERROR: the trait bound `<(RustaceansAreAwesome,) as HasAssoc>::Assoc: Clone` is not satisfied //~| NOTE: required for `<(RustaceansAreAwesome,) as HasAssoc>::Assoc` to implement `ToOwned` } ``` This fails to prove `<(RustaceansAreAwesome,) as HasAssoc>::Assoc: Owned` because it can't normalize that alias to `str`. The followup will re-add projections as necessary for this in a hopefully-non-breaking way.

…uwer Rollup of 12 pull requests Successful merges: - #163462 (Fix COFF renaming of decorated (stdcall/fastcall/vectorcall) exports) - #163855 (Include enclosing item's context on const errors) - #163861 (Run LLDB debuginfo tests on `x86_64-mingw`) - #161201 (Speed up tidy again) - #163538 (Add `rustc::missing_generic_type_visitable` lint) - #163617 (mips: make `Complex<T>` ABI match GCC) - #163772 (comptime fn error: suggest wrapping in const block) - #163832 (reject non-async coroutine closures as async callables) - #163958 (only make `RustaceansAreAwesome` satisfy trait clauses) - #163974 (Condense AdtDef lang item checks into one match) - #163979 (Add `bf16` to arm features) - #163989 (Revert "compiletest: stream output of executor process when --no-capture is set") Failed merges: - #163972 (const-eval: ICE when we hit a non-const fn)

…uwer Rollup of 19 pull requests Successful merges: - #156112 (Distinguish `repr(C)` ZSTs from others in ABI computation) - #157941 (Deny partial `-Z stack-protector` by default in all editions) - #163462 (Fix COFF renaming of decorated (stdcall/fastcall/vectorcall) exports) - #163855 (Include enclosing item's context on const errors) - #163861 (Run LLDB debuginfo tests on `x86_64-mingw`) - #163913 ( Silence redundant failed obligations on the same statement) - #161201 (Speed up tidy again) - #163380 (Tweak "name not found" resolution error when it happens from within a derive expansion) - #163538 (Add `rustc::missing_generic_type_visitable` lint) - #163617 (mips: make `Complex<T>` ABI match GCC) - #163772 (comptime fn error: suggest wrapping in const block) - #163813 (use pre-borrowck typing env for early MIR validation) - #163924 (replace instances of NonNull::new(&mut x).expect("...") with NonNull::from_mut) - #163958 (only make `RustaceansAreAwesome` satisfy trait clauses) - #163960 (vexos: clear .bss from assembly) - #163974 (Condense AdtDef lang item checks into one match) - #163979 (Add `bf16` to arm features) - #163989 (Revert "compiletest: stream output of executor process when --no-capture is set") - #163995 (m68k-unknown-none-elf: Remove code model) Failed merges: - #163832 (reject non-async coroutine closures as async callables) - #163972 (const-eval: ICE when we hit a non-const fn)

Rollup merge of #163958 - dianne:fix-rustaceansareawesome-take-2-partial, r=oli-obk only make `RustaceansAreAwesome` satisfy trait clauses Fixes #163550 but unfortunately partially un-fixes a variant of #161621 that hadn't been reported. I have a followup to re-fix that, but I ended up deciding that it would probably be easier to review separately; I'll open a PR for that later. The variant in question: ```rust trait HasAssoc { type Assoc; } trait Parent<T> {} trait Trait where (Self,): HasAssoc<Assoc = str>, Self: Parent<<<(Self,) as HasAssoc>::Assoc as ToOwned>::Owned>, { fn f(&self); //~^ ERROR: the trait bound `<(RustaceansAreAwesome,) as HasAssoc>::Assoc: Clone` is not satisfied //~| NOTE: required for `<(RustaceansAreAwesome,) as HasAssoc>::Assoc` to implement `ToOwned` } ``` This fails to prove `<(RustaceansAreAwesome,) as HasAssoc>::Assoc: Owned` because it can't normalize that alias to `str`. The followup will re-add projections as necessary for this in a hopefully-non-breaking way.

…uwer Rollup of 19 pull requests Successful merges: - rust-lang/rust#156112 (Distinguish `repr(C)` ZSTs from others in ABI computation) - rust-lang/rust#157941 (Deny partial `-Z stack-protector` by default in all editions) - rust-lang/rust#163462 (Fix COFF renaming of decorated (stdcall/fastcall/vectorcall) exports) - rust-lang/rust#163855 (Include enclosing item's context on const errors) - rust-lang/rust#163861 (Run LLDB debuginfo tests on `x86_64-mingw`) - rust-lang/rust#163913 ( Silence redundant failed obligations on the same statement) - rust-lang/rust#161201 (Speed up tidy again) - rust-lang/rust#163380 (Tweak "name not found" resolution error when it happens from within a derive expansion) - rust-lang/rust#163538 (Add `rustc::missing_generic_type_visitable` lint) - rust-lang/rust#163617 (mips: make `Complex<T>` ABI match GCC) - rust-lang/rust#163772 (comptime fn error: suggest wrapping in const block) - rust-lang/rust#163813 (use pre-borrowck typing env for early MIR validation) - rust-lang/rust#163924 (replace instances of NonNull::new(&mut x).expect("...") with NonNull::from_mut) - rust-lang/rust#163958 (only make `RustaceansAreAwesome` satisfy trait clauses) - rust-lang/rust#163960 (vexos: clear .bss from assembly) - rust-lang/rust#163974 (Condense AdtDef lang item checks into one match) - rust-lang/rust#163979 (Add `bf16` to arm features) - rust-lang/rust#163989 (Revert "compiletest: stream output of executor process when --no-capture is set") - rust-lang/rust#163995 (m68k-unknown-none-elf: Remove code model) Failed merges: - rust-lang/rust#163832 (reject non-async coroutine closures as async callables) - rust-lang/rust#163972 (const-eval: ICE when we hit a non-const fn)

elide potentially-problematic projection clauses

df42c7b

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 Oct 7, 2026

dianne commented Oct 7, 2026

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rustbot assigned oli-obk Oct 8, 2026

dianne marked this pull request as ready for review October 8, 2026 00:08

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Oct 8, 2026

oli-obk approved these changes Oct 8, 2026

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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 Oct 8, 2026

JonathanBrouwer mentioned this pull request Oct 8, 2026

Rollup of 8 pull requests #163984

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JonathanBrouwer mentioned this pull request Oct 8, 2026

Rollup of 9 pull requests #163987

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JonathanBrouwer mentioned this pull request Oct 8, 2026

Rollup of 12 pull requests #163993

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JonathanBrouwer mentioned this pull request Oct 8, 2026

Rollup of 19 pull requests #164005

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rust-bors Bot merged commit e8b6023 into rust-lang:main Oct 8, 2026
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rustbot added this to the 1.101.0 milestone Oct 8, 2026

github-actions Bot mentioned this pull request Oct 9, 2026

Toolchain upgrade to nightly-2026-10-09 flux-rs/flux#1811

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dianne deleted the fix-rustaceansareawesome-take-2-partial branch October 9, 2026 03:04

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only make `RustaceansAreAwesome` satisfy trait clauses - #163958

only make `RustaceansAreAwesome` satisfy trait clauses#163958
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