[E0117]: non-local ADT/primitive label in trait position names the type instead of attributing it to the foreign trait

[Omar1H1]

Code

impl PartialEq for u32 {
    fn eq(&self, _other: &Self) -> bool {
        todo!()
    }
}

Current output

error[E0117]: only traits defined in the current crate can be implemented for primitive types
	--> src/lib.rs:1:1
	 |
	1 | impl PartialEq for u32 {
	 | ^^^^^---------^^^^^---
	 |      |             |
	 |      |             `u32` is not defined in the current crate
	 |      `u32` is not defined in the current crate
	 |
	 = note: impl doesn't have any local type before any uncovered type parameters
	 = note: for more information see https://doc.rust-lang.org/reference/items/implementations.html#orphan-rules
	 = note: define and implement a trait or new type instead

	For more information about this error, try `rustc --explain E0117`.

Desired output

| impl PartialEq for u32 {
  | ^^^^^---------^^^^^---
  |      |             |
  |      |             `u32` is not defined in the current crate
  |      this is not defined in the current crate because this is a foreign trait

Rationale and extra context

Original diagnosis in this issue was incorrect. see the comment below for the corrected root cause. Leaving the original text below for context.

In compiler/rustc_hir_analysis/src/coherence/orphan.rs, emit_orphan_check_error iterates through non-local input types. When processing the trait (is_target_ty == IsFirstInputType::No), it passes the target type's subdiagnostic message template (OnlyCurrentTraitsTy), causing the type name (u32) to be formatted for both the type and trait span labels.

Other cases

Rust Version

❯ rustc --version --verbose
rustc 1.97.1 (8bab26f4f 2026-07-14)
binary: rustc
commit-hash: 8bab26f4f68e0e26f0bb7960be334d5b520ea452
commit-date: 2026-07-14
host: x86_64-unknown-linux-gnu
release: 1.97.1
LLVM version: 22.1.6

Anything else?

I would like to work on a PR to fix this issue !

[rperier]

Feel free to assign it to yourself then, see https://rustc-dev-guide.rust-lang.org/rustbot.html?highlight=assign#issue-claiming

[Omar1H1]

@rustbot claim

[Omar1H1]

Correcting my original diagnosis:

After digging further into compiler/rustc_hir_analysis/src/coherence/orphan.rs, the issue turned out to be much narrower than I thought. The second label is not applying a type template to the trait by mistake.

emit_orphan_check_error already tracks an is_foreign flag, which is true whenever a non-local type appears in one of the trait's parameter positions rather than in Self. Match arms for Slice, Array, and Tuple already use is_foreign to switch their label to "this is not defined in the current crate because this is a foreign trait" instead of naming the type.

However, the Adt arm and the catch-all _ arm (which catches primitives like u32) never check is_foreign. They always name the type.
I confirmed this behavior is positional rather than related to Rhs defaulting by testing impl PartialEq<[i32; 3]> for u32 on the Playground. The array argument gets the "foreign trait".

Fix: Extend the is_foreign check to the Adt and _ match arms:

ty::Adt(adt_def, _) => {
    if is_foreign {
        diag.subdiagnostic(diagnostics::OnlyCurrentTraitsForeign { span });
    } else {
        diag.subdiagnostic(diagnostics::OnlyCurrentTraitsAdt {
            span,
            name: tcx.def_path_str(adt_def.did()),
        });
    }
}
_ => {
    if is_foreign {
        diag.subdiagnostic(diagnostics::OnlyCurrentTraitsForeign { span });
    } else {
        diag.subdiagnostic(diagnostics::OnlyCurrentTraitsTy { span, ty });
    }
}

I ran the full UI test suite across every test containing "is not defined in the current crate" (13 files under tests/ui/, not just coherence/). Exactly 7 .stderr snapshots changed, all following the exact same pattern: a non-Self ADT or primitive label switches to the "foreign trait". Every Self-position label and every unrelated diagnostic (like E0119 in shared files) remains untouched:

• tests/ui/coherence/coherence-orphan.stderr
• tests/ui/coherence/coherence-pair-covered-uncovered-1.stderr
• tests/ui/coherence/impl-foreign-for-foreign[foreign].stderr
• tests/ui/coherence/impl-foreign[foreign]-for-foreign.stderr
• tests/ui/coherence/impl-foreign[fundemental[foreign]]-for-foreign.stderr
• tests/ui/coherence/orphan-check-error-reporting-ty-var.stderr
• tests/ui/traits/const-traits/const-and-non-const-impl.stderr

I'll open a PR with this fix and add a new UI regression test to cover the PartialEq and Add cases that triggered this.