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Add a diagnostic for similarly named traits #144674

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58 changes: 14 additions & 44 deletions compiler/rustc_hir_typeck/src/method/suggest.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3478,7 +3478,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
err,
pick.item.def_id,
rcvr.hir_id,
Some(*rcvr_ty),
*rcvr_ty,
);
if pick.autoderefs == 0 && !trait_in_other_version_found {
err.span_label(
Expand Down Expand Up @@ -3686,6 +3686,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
// same crate.

let rcvr_ty = self.node_ty_opt(ty.hir_id);
let Some(rcvr_ty) = rcvr_ty else {
return;
};
trait_in_other_version_found = self
.detect_and_explain_multiple_crate_versions_of_trait_item(
err,
Expand Down Expand Up @@ -4089,7 +4092,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
err: &mut Diag<'_>,
item_def_id: DefId,
hir_id: hir::HirId,
rcvr_ty: Option<Ty<'_>>,
rcvr_ty: Ty<'tcx>,
) -> bool {
let hir_id = self.tcx.parent_hir_id(hir_id);
let Some(traits) = self.tcx.in_scope_traits(hir_id) else { return false };
Expand All @@ -4100,49 +4103,16 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
if !self.tcx.is_trait(trait_def_id) {
return false;
}
let krate = self.tcx.crate_name(trait_def_id.krate);
let name = self.tcx.item_name(trait_def_id);
let candidates: Vec<_> = traits
.iter()
.filter(|c| {
c.def_id.krate != trait_def_id.krate
&& self.tcx.crate_name(c.def_id.krate) == krate
&& self.tcx.item_name(c.def_id) == name
})
.map(|c| (c.def_id, c.import_ids.get(0).cloned()))
.collect();
if candidates.is_empty() {
let hir::Node::Expr(rcvr) = self.tcx.hir_node(hir_id) else {
return false;
}
let item_span = self.tcx.def_span(item_def_id);
let msg = format!(
"there are multiple different versions of crate `{krate}` in the dependency graph",
);
let trait_span = self.tcx.def_span(trait_def_id);
let mut multi_span: MultiSpan = trait_span.into();
multi_span.push_span_label(trait_span, "this is the trait that is needed".to_string());
let descr = self.tcx.associated_item(item_def_id).descr();
let rcvr_ty =
rcvr_ty.map(|t| format!("`{t}`")).unwrap_or_else(|| "the receiver".to_string());
multi_span
.push_span_label(item_span, format!("the {descr} is available for {rcvr_ty} here"));
for (def_id, import_def_id) in candidates {
if let Some(import_def_id) = import_def_id {
multi_span.push_span_label(
self.tcx.def_span(import_def_id),
format!(
"`{name}` imported here doesn't correspond to the right version of crate \
`{krate}`",
),
);
}
multi_span.push_span_label(
self.tcx.def_span(def_id),
"this is the trait that was imported".to_string(),
);
}
err.span_note(multi_span, msg);
true
};
let trait_ref = ty::TraitRef::new(self.tcx, trait_def_id, [rcvr_ty]);
let trait_pred = ty::Binder::dummy(ty::TraitPredicate {
trait_ref,
polarity: ty::PredicatePolarity::Positive,
});
let obligation = Obligation::new(self.tcx, self.misc(rcvr.span), self.param_env, trait_ref);
self.err_ctxt().note_different_trait_with_same_name(err, &obligation, trait_pred)
}

/// issue #102320, for `unwrap_or` with closure as argument, suggest `unwrap_or_else`
Expand Down
246 changes: 115 additions & 131 deletions compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -12,7 +12,7 @@ use rustc_errors::{
Applicability, Diag, ErrorGuaranteed, Level, MultiSpan, StashKey, StringPart, Suggestions,
pluralize, struct_span_code_err,
};
use rustc_hir::def_id::{DefId, LOCAL_CRATE, LocalDefId};
use rustc_hir::def_id::{DefId, LocalDefId};
use rustc_hir::intravisit::Visitor;
use rustc_hir::{self as hir, LangItem, Node};
use rustc_infer::infer::{InferOk, TypeTrace};
Expand Down Expand Up @@ -467,7 +467,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
span,
leaf_trait_predicate,
);
self.note_version_mismatch(&mut err, leaf_trait_predicate);
self.note_different_trait_with_same_name(&mut err, &obligation, leaf_trait_predicate);
self.suggest_remove_await(&obligation, &mut err);
self.suggest_derive(&obligation, &mut err, leaf_trait_predicate);

Expand Down Expand Up @@ -1948,115 +1948,6 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
impl_candidates
};

// We'll check for the case where the reason for the mismatch is that the trait comes from
// one crate version and the type comes from another crate version, even though they both
// are from the same crate.
let trait_def_id = trait_pred.def_id();
let trait_name = self.tcx.item_name(trait_def_id);
let crate_name = self.tcx.crate_name(trait_def_id.krate);
if let Some(other_trait_def_id) = self.tcx.all_traits_including_private().find(|def_id| {
trait_name == self.tcx.item_name(trait_def_id)
&& trait_def_id.krate != def_id.krate
&& crate_name == self.tcx.crate_name(def_id.krate)
}) {
// We've found two different traits with the same name, same crate name, but
// different crate `DefId`. We highlight the traits.

let found_type =
if let ty::Adt(def, _) = trait_pred.self_ty().skip_binder().peel_refs().kind() {
Some(def.did())
} else {
None
};
let candidates = if impl_candidates.is_empty() {
alternative_candidates(trait_def_id)
} else {
impl_candidates.into_iter().map(|cand| cand.trait_ref).collect()
};
let mut span: MultiSpan = self.tcx.def_span(trait_def_id).into();
span.push_span_label(self.tcx.def_span(trait_def_id), "this is the required trait");
for (sp, label) in [trait_def_id, other_trait_def_id]
.iter()
// The current crate-version might depend on another version of the same crate
// (Think "semver-trick"). Do not call `extern_crate` in that case for the local
// crate as that doesn't make sense and ICEs (#133563).
.filter(|def_id| !def_id.is_local())
.filter_map(|def_id| self.tcx.extern_crate(def_id.krate))
.map(|data| {
let dependency = if data.dependency_of == LOCAL_CRATE {
"direct dependency of the current crate".to_string()
} else {
let dep = self.tcx.crate_name(data.dependency_of);
format!("dependency of crate `{dep}`")
};
(
data.span,
format!("one version of crate `{crate_name}` used here, as a {dependency}"),
)
})
{
span.push_span_label(sp, label);
}
let mut points_at_type = false;
if let Some(found_type) = found_type {
span.push_span_label(
self.tcx.def_span(found_type),
"this type doesn't implement the required trait",
);
for trait_ref in candidates {
if let ty::Adt(def, _) = trait_ref.self_ty().peel_refs().kind()
&& let candidate_def_id = def.did()
&& let Some(name) = self.tcx.opt_item_name(candidate_def_id)
&& let Some(found) = self.tcx.opt_item_name(found_type)
&& name == found
&& candidate_def_id.krate != found_type.krate
&& self.tcx.crate_name(candidate_def_id.krate)
== self.tcx.crate_name(found_type.krate)
{
// A candidate was found of an item with the same name, from two separate
// versions of the same crate, let's clarify.
let candidate_span = self.tcx.def_span(candidate_def_id);
span.push_span_label(
candidate_span,
"this type implements the required trait",
);
points_at_type = true;
}
}
}
span.push_span_label(self.tcx.def_span(other_trait_def_id), "this is the found trait");
err.highlighted_span_note(
span,
vec![
StringPart::normal("there are ".to_string()),
StringPart::highlighted("multiple different versions".to_string()),
StringPart::normal(" of crate `".to_string()),
StringPart::highlighted(format!("{crate_name}")),
StringPart::normal("` in the dependency graph".to_string()),
],
);
if points_at_type {
// We only clarify that the same type from different crate versions are not the
// same when we *find* the same type coming from different crate versions, otherwise
// it could be that it was a type provided by a different crate than the one that
// provides the trait, and mentioning this adds verbosity without clarification.
err.highlighted_note(vec![
StringPart::normal(
"two types coming from two different versions of the same crate are \
different types "
.to_string(),
),
StringPart::highlighted("even if they look the same".to_string()),
]);
}
err.highlighted_help(vec![
StringPart::normal("you can use `".to_string()),
StringPart::highlighted("cargo tree".to_string()),
StringPart::normal("` to explore your dependency tree".to_string()),
]);
return true;
}

if let [single] = &impl_candidates {
// If we have a single implementation, try to unify it with the trait ref
// that failed. This should uncover a better hint for what *is* implemented.
Expand Down Expand Up @@ -2421,10 +2312,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
}
}

/// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
/// with the same path as `trait_ref`, a help message about
/// a probable version mismatch is added to `err`
fn note_version_mismatch(
fn check_same_trait_different_version(
&self,
err: &mut Diag<'_>,
trait_pred: ty::PolyTraitPredicate<'tcx>,
Expand All @@ -2441,38 +2329,134 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
trait_impls
};

let krate = self.tcx.crate_name(trait_pred.def_id().krate);
let name = self.tcx.item_name(trait_pred.def_id());
let required_trait_path = self.tcx.def_path_str(trait_pred.def_id());
let traits_with_same_path: UnordSet<_> = self
.tcx
.visible_traits()
.filter(|trait_def_id| *trait_def_id != trait_pred.def_id())
.filter(|trait_def_id| {
trait_def_id.krate != trait_pred.def_id().krate
&& (self.tcx.def_path_str(trait_def_id) == required_trait_path
|| self.tcx.crate_name(trait_def_id.krate) == krate
&& self.tcx.item_name(trait_def_id) == name)
Comment on lines +2340 to +2342
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when is self.tcx.crate_name(trait_def_id.krate) == krate && self.tcx.item_name(trait_def_id) == name false but self.tcx.def_path_str(trait_def_id) == required_trait_path holds?

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It used by tests/ui/traits/bound/same-crate-name.rs , disabling this case makes the test fail.

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so that's crate::mod::Trait and crate::Trait?

Wait, disabling which case? Each of the two cases should handle some distinct cases I would expect, what are the test covering eacvh of them and could we generalize the condition even further. It feels weird to have 2 different conditions if the rest of the diagnostic is exactly the same

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@rperier rperier Oct 7, 2025 •
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No, I am not talking about my test "tests/ui/traits/similarly_named_trait.rs" , but about https://github.com/rust-lang/rust/blob/master/tests/ui/traits/bound/same-crate-name.rs#L10 instead. Removing the line "self.tcx.def_path_str(trait_def_id) == required_trait_path" makes this test fail. I think the use case covered by this test is real, isn't it ?

})
.map(|trait_def_id| (self.tcx.def_path_str(trait_def_id), trait_def_id))
.filter(|(p, _)| *p == required_trait_path)
.collect();

let traits_with_same_path =
traits_with_same_path.into_items().into_sorted_stable_ord_by_key(|(p, _)| p);
let mut suggested = false;
for (_, trait_with_same_path) in traits_with_same_path {
let trait_impls = get_trait_impls(trait_with_same_path);
if trait_impls.is_empty() {
continue;
}
let impl_spans: Vec<_> =
trait_impls.iter().map(|impl_def_id| self.tcx.def_span(*impl_def_id)).collect();
err.span_help(
impl_spans,
format!("trait impl{} with same name found", pluralize!(trait_impls.len())),
let mut trait_is_impl = false;

if !traits_with_same_path.is_empty() {
let msg = format!(
"there are multiple different versions of crate `{krate}` in the dependency graph"
);
let trait_crate = self.tcx.crate_name(trait_with_same_path.krate);
let crate_msg =
format!("perhaps two different versions of crate `{trait_crate}` are being used?");
err.note(crate_msg);
let mut span: MultiSpan = self.tcx.def_span(trait_pred.def_id()).into();
span.push_span_label(
self.tcx.def_span(trait_pred.def_id()),
"this is the required trait",
);
suggested = true;
for (_, trait_with_same_path) in &traits_with_same_path {
let trait_impls = get_trait_impls(*trait_with_same_path);
if trait_impls.is_empty() {
continue;
}

for candidate_def_id in trait_impls {
let Some(impl_trait_header) = self.tcx.impl_trait_header(candidate_def_id)
else {
continue;
};
let candidate_span =
self.tcx.def_span(impl_trait_header.trait_ref.skip_binder().def_id);
span.push_span_label(candidate_span, "this is the implemented trait");
trait_is_impl = true;
}
}
if !trait_is_impl {
for (_, def_id) in traits_with_same_path {
span.push_span_label(
self.tcx.def_span(def_id),
"this is the trait that was imported",
);
}
}
err.span_note(span, msg);
}
suggested
}

fn check_same_name_different_path(
&self,
err: &mut Diag<'_>,
obligation: &PredicateObligation<'tcx>,
trait_pred: ty::PolyTraitPredicate<'tcx>,
) -> bool {
let mut suggested = false;
let trait_def_id = trait_pred.def_id();
let trait_has_same_params = |other_trait_def_id: DefId| -> bool {
let trait_generics = self.tcx.generics_of(trait_def_id);
let other_trait_generics = self.tcx.generics_of(other_trait_def_id);

if trait_generics.count() != other_trait_generics.count() {
return false;
}
trait_generics.own_params.iter().zip(other_trait_generics.own_params.iter()).all(
|(a, b)| {
(matches!(a.kind, ty::GenericParamDefKind::Type { .. })
&& matches!(b.kind, ty::GenericParamDefKind::Type { .. }))
|| (matches!(a.kind, ty::GenericParamDefKind::Lifetime,)
&& matches!(b.kind, ty::GenericParamDefKind::Lifetime))
|| (matches!(a.kind, ty::GenericParamDefKind::Const { .. })
&& matches!(b.kind, ty::GenericParamDefKind::Const { .. }))
},
)
};
let trait_name = self.tcx.item_name(trait_def_id);
if let Some(other_trait_def_id) = self.tcx.all_traits_including_private().find(|def_id| {
trait_def_id != *def_id
&& trait_name == self.tcx.item_name(def_id)
&& trait_has_same_params(*def_id)
&& self.predicate_must_hold_modulo_regions(&Obligation::new(
self.tcx,
obligation.cause.clone(),
obligation.param_env,
trait_pred.map_bound(|tr| ty::TraitPredicate {
trait_ref: ty::TraitRef::new(self.tcx, *def_id, tr.trait_ref.args),
..tr
}),
))
}) {
err.note(format!(
"`{}` implements similarly named `{}`, but not `{}`",
trait_pred.self_ty(),
self.tcx.def_path_str(other_trait_def_id),
trait_pred.print_modifiers_and_trait_path()
));
suggested = true;
}
suggested
}

/// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
/// with the same path as `trait_ref`, a help message about a multiple different
/// versions of the same crate is added to `err`. Otherwise if it implements another
/// trait with the same name, a note message about a similarly named trait is added to `err`.
pub fn note_different_trait_with_same_name(
&self,
err: &mut Diag<'_>,
obligation: &PredicateObligation<'tcx>,
trait_pred: ty::PolyTraitPredicate<'tcx>,
) -> bool {
if self.check_same_trait_different_version(err, trait_pred) {
return true;
}
self.check_same_name_different_path(err, obligation, trait_pred)
}

/// Creates a `PredicateObligation` with `new_self_ty` replacing the existing type in the
/// `trait_ref`.
///
Expand Down
2 changes: 1 addition & 1 deletion compiler/rustc_trait_selection/src/error_reporting/traits/mod.rs
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Original file line number Diff line number Diff line change
@@ -1,6 +1,6 @@
pub mod ambiguity;
pub mod call_kind;
mod fulfillment_errors;
pub mod fulfillment_errors;
pub mod on_unimplemented;
pub mod on_unimplemented_condition;
pub mod on_unimplemented_format;
Expand Down
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