diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index e4aabbdb7ede7..727285e4927a0 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -1361,7 +1361,17 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
) => false,
(ParamCandidate(other), ParamCandidate(victim)) => {
- if other.value == victim.value && victim.constness == Constness::NotConst {
+ let value_same_except_bound_vars = other.value.skip_binder()
+ == victim.value.skip_binder()
+ && !other.value.skip_binder().has_escaping_bound_vars();
+ if value_same_except_bound_vars {
+ // See issue #84398. In short, we can generate multiple ParamCandidates which are
+ // the same except for unused bound vars. Just pick the one with the fewest bound vars
+ // or the current one if tied (they should both evaluate to the same answer). This is
+ // probably best characterized as a "hack", since we might prefer to just do our
+ // best to *not* create essentially duplicate candidates in the first place.
+ other.value.bound_vars().len() <= victim.value.bound_vars().len()
+ } else if other.value == victim.value && victim.constness == Constness::NotConst {
// Drop otherwise equivalent non-const candidates in favor of const candidates.
true
} else {
diff --git a/compiler/rustc_typeck/src/check/method/suggest.rs b/compiler/rustc_typeck/src/check/method/suggest.rs
index 73e35f0171aa7..b2e4e7a981d20 100644
--- a/compiler/rustc_typeck/src/check/method/suggest.rs
+++ b/compiler/rustc_typeck/src/check/method/suggest.rs
@@ -579,6 +579,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
}
let mut restrict_type_params = false;
+ let mut unsatisfied_bounds = false;
if !unsatisfied_predicates.is_empty() {
let def_span = |def_id| {
self.tcx.sess.source_map().guess_head_span(self.tcx.def_span(def_id))
@@ -739,6 +740,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
err.note(&format!(
"the following trait bounds were not satisfied:\n{bound_list}"
));
+ unsatisfied_bounds = true;
}
}
@@ -752,6 +754,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
source,
out_of_scope_traits,
&unsatisfied_predicates,
+ unsatisfied_bounds,
);
}
@@ -984,9 +987,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
source: SelfSource<'tcx>,
valid_out_of_scope_traits: Vec<DefId>,
unsatisfied_predicates: &[(ty::Predicate<'tcx>, Option<ty::Predicate<'tcx>>)],
+ unsatisfied_bounds: bool,
) {
let mut alt_rcvr_sugg = false;
- if let SelfSource::MethodCall(rcvr) = source {
+ if let (SelfSource::MethodCall(rcvr), false) = (source, unsatisfied_bounds) {
debug!(?span, ?item_name, ?rcvr_ty, ?rcvr);
let skippable = [
self.tcx.lang_items().clone_trait(),
diff --git a/src/stage0.txt b/src/stage0.txt
index 3a76177474908..231e66719d00a 100644
--- a/src/stage0.txt
+++ b/src/stage0.txt
@@ -12,7 +12,7 @@
# stable release's version number. `date` is the date where the release we're
# bootstrapping off was released.
-date: 2021-05-04
+date: 2021-05-06
rustc: 1.52.0
# We use a nightly rustfmt to format the source because it solves some
@@ -39,4 +39,4 @@ rustc: 1.52.0
# looking at a beta source tarball and it's uncommented we'll shortly comment it
# out.
-dev: 1
+#dev: 1
diff --git a/src/test/ui/lifetimes/issue-84398.rs b/src/test/ui/lifetimes/issue-84398.rs
new file mode 100644
index 0000000000000..1912fa59b7990
--- /dev/null
+++ b/src/test/ui/lifetimes/issue-84398.rs
@@ -0,0 +1,20 @@
+// check-pass
+
+pub trait Deserialize<'de>: Sized {}
+pub trait DeserializeOwned: for<'de> Deserialize<'de> {}
+
+pub trait Extensible {
+ type Config;
+}
+
+// The `C` here generates a `C: Sized` candidate
+pub trait Installer<C> {
+ fn init<B: Extensible<Config = C>>(&mut self) -> ()
+ where
+ // This clause generates a `for<'de> C: Sized` candidate
+ B::Config: DeserializeOwned,
+ {
+ }
+}
+
+fn main() {}
diff --git a/src/test/ui/suggestions/import-trait-for-method-call.rs b/src/test/ui/suggestions/import-trait-for-method-call.rs
index 646f68dea14e8..4dbadbdf98206 100644
--- a/src/test/ui/suggestions/import-trait-for-method-call.rs
+++ b/src/test/ui/suggestions/import-trait-for-method-call.rs
@@ -6,4 +6,11 @@ fn next_u64() -> u64 {
h.finish() //~ ERROR no method named `finish` found for struct `DefaultHasher`
}
-fn main() {}
+trait Bar {}
+impl Bar for String {}
+
+fn main() {
+ let s = String::from("hey");
+ let x: &dyn Bar = &s;
+ x.as_ref(); //~ ERROR the method `as_ref` exists for reference `&dyn Bar`, but its trait bounds
+}
diff --git a/src/test/ui/suggestions/import-trait-for-method-call.stderr b/src/test/ui/suggestions/import-trait-for-method-call.stderr
index f3ae20552f3d5..a2b9b9d14ab09 100644
--- a/src/test/ui/suggestions/import-trait-for-method-call.stderr
+++ b/src/test/ui/suggestions/import-trait-for-method-call.stderr
@@ -15,6 +15,22 @@ help: the following trait is implemented but not in scope; perhaps add a `use` f
LL | use std::hash::Hasher;
|
-error: aborting due to previous error
+error[E0599]: the method `as_ref` exists for reference `&dyn Bar`, but its trait bounds were not satisfied
+ --> $DIR/import-trait-for-method-call.rs:15:7
+ |
+LL | trait Bar {}
+ | --------- doesn't satisfy `dyn Bar: AsRef<_>`
+...
+LL | x.as_ref();
+ | ^^^^^^ method cannot be called on `&dyn Bar` due to unsatisfied trait bounds
+ |
+ = note: the following trait bounds were not satisfied:
+ `dyn Bar: AsRef<_>`
+ which is required by `&dyn Bar: AsRef<_>`
+ = help: items from traits can only be used if the trait is implemented and in scope
+ = note: the following trait defines an item `as_ref`, perhaps you need to implement it:
+ candidate #1: `AsRef`
+
+error: aborting due to 2 previous errors
For more information about this error, try `rustc --explain E0599`.