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/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 { + fn init>(&mut self) -> () + where + // This clause generates a `for<'de> C: Sized` candidate + B::Config: DeserializeOwned, + { + } +} + +fn main() {}