From 9f0693969a0ac0a0193c7c367e3292b5315b2747 Mon Sep 17 00:00:00 2001 From: Jack Huey Date: Sun, 25 Apr 2021 15:11:49 -0400 Subject: [PATCH] Deduplicate ParamCandidates with the same value except for bound vars --- .../src/traits/select/mod.rs | 12 ++++++++++- src/test/ui/lifetimes/issue-84398.rs | 20 +++++++++++++++++++ 2 files changed, 31 insertions(+), 1 deletion(-) create mode 100644 src/test/ui/lifetimes/issue-84398.rs diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs index e4aabbdb7ed..c9ba8e6dc8c 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 current one (the 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. + true + } 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 00000000000..1912fa59b79 --- /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() {}