Rollup merge of #108842 - compiler-errors:non_lifetime_binders-object-safe, r=b-naber

Enforce non-lifetime-binders in supertrait preds are not object safe

We can't construct vtables for these supertraits.

2 files changed, 31 insertions, 3 deletions

diff --git a/compiler/rustc_middle/src/traits/mod.rs b/compiler/rustc_middle/src/traits/mod.rs
index fb3e9cb1263..833402abfc4 100644
--- a/compiler/rustc_middle/src/traits/mod.rs
+++ b/compiler/rustc_middle/src/traits/mod.rs
@@ -897,6 +897,9 @@ pub enum ObjectSafetyViolation {
     /// (e.g., `trait Foo : Bar<Self>`).
     SupertraitSelf(SmallVec<[Span; 1]>),
 
+    // Supertrait has a non-lifetime `for<T>` binder.
+    SupertraitNonLifetimeBinder(SmallVec<[Span; 1]>),
+
     /// Method has something illegal.
     Method(Symbol, MethodViolationCode, Span),
 
@@ -919,6 +922,9 @@ impl ObjectSafetyViolation {
                         .into()
                 }
             }
+            ObjectSafetyViolation::SupertraitNonLifetimeBinder(_) => {
+                format!("where clause cannot reference non-lifetime `for<...>` variables").into()
+            }
             ObjectSafetyViolation::Method(name, MethodViolationCode::StaticMethod(_), _) => {
                 format!("associated function `{}` has no `self` parameter", name).into()
             }
@@ -969,7 +975,9 @@ impl ObjectSafetyViolation {
 
     pub fn solution(&self, err: &mut Diagnostic) {
         match self {
-            ObjectSafetyViolation::SizedSelf(_) | ObjectSafetyViolation::SupertraitSelf(_) => {}
+            ObjectSafetyViolation::SizedSelf(_)
+            | ObjectSafetyViolation::SupertraitSelf(_)
+            | ObjectSafetyViolation::SupertraitNonLifetimeBinder(..) => {}
             ObjectSafetyViolation::Method(
                 name,
                 MethodViolationCode::StaticMethod(Some((add_self_sugg, make_sized_sugg))),
@@ -1023,7 +1031,8 @@ impl ObjectSafetyViolation {
         // diagnostics use a `note` instead of a `span_label`.
         match self {
             ObjectSafetyViolation::SupertraitSelf(spans)
-            | ObjectSafetyViolation::SizedSelf(spans) => spans.clone(),
+            | ObjectSafetyViolation::SizedSelf(spans)
+            | ObjectSafetyViolation::SupertraitNonLifetimeBinder(spans) => spans.clone(),
             ObjectSafetyViolation::AssocConst(_, span)
             | ObjectSafetyViolation::GAT(_, span)
             | ObjectSafetyViolation::Method(_, _, span)
diff --git a/compiler/rustc_trait_selection/src/traits/object_safety.rs b/compiler/rustc_trait_selection/src/traits/object_safety.rs
index a5def4151bf..038f8964471 100644
--- a/compiler/rustc_trait_selection/src/traits/object_safety.rs
+++ b/compiler/rustc_trait_selection/src/traits/object_safety.rs
@@ -17,10 +17,10 @@ use rustc_errors::{DelayDm, FatalError, MultiSpan};
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_middle::ty::subst::{GenericArg, InternalSubsts};
-use rustc_middle::ty::ToPredicate;
 use rustc_middle::ty::{
     self, EarlyBinder, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitor,
 };
+use rustc_middle::ty::{ToPredicate, TypeVisitableExt};
 use rustc_session::lint::builtin::WHERE_CLAUSES_OBJECT_SAFETY;
 use rustc_span::symbol::Symbol;
 use rustc_span::Span;
@@ -139,6 +139,10 @@ fn object_safety_violations_for_trait(
     if !spans.is_empty() {
         violations.push(ObjectSafetyViolation::SupertraitSelf(spans));
     }
+    let spans = super_predicates_have_non_lifetime_binders(tcx, trait_def_id);
+    if !spans.is_empty() {
+        violations.push(ObjectSafetyViolation::SupertraitNonLifetimeBinder(spans));
+    }
 
     violations.extend(
         tcx.associated_items(trait_def_id)
@@ -348,6 +352,21 @@ fn predicate_references_self<'tcx>(
     }
 }
 
+fn super_predicates_have_non_lifetime_binders(
+    tcx: TyCtxt<'_>,
+    trait_def_id: DefId,
+) -> SmallVec<[Span; 1]> {
+    // If non_lifetime_binders is disabled, then exit early
+    if !tcx.features().non_lifetime_binders {
+        return SmallVec::new();
+    }
+    tcx.super_predicates_of(trait_def_id)
+        .predicates
+        .iter()
+        .filter_map(|(pred, span)| pred.has_non_region_late_bound().then_some(*span))
+        .collect()
+}
+
 fn trait_has_sized_self(tcx: TyCtxt<'_>, trait_def_id: DefId) -> bool {
     generics_require_sized_self(tcx, trait_def_id)
 }