Stop being so bail-y in candidate assembly

Author: compiler-errors

compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs

@@ -91,14 +91,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             } else if tcx.is_lang_item(def_id, LangItem::Sized) {
                 // Sized is never implementable by end-users, it is
                 // always automatically computed.
-
-                // FIXME: Consider moving this check to the top level as it
-                // may also be useful for predicates other than `Sized`
-                // Error type cannot possibly implement `Sized` (fixes #123154)
-                if let Err(e) = obligation.predicate.skip_binder().self_ty().error_reported() {
-                    return Err(SelectionError::Overflow(e.into()));
-                }
-
                 let sized_conditions = self.sized_conditions(obligation);
                 self.assemble_builtin_bound_candidates(sized_conditions, &mut candidates);
             } else if tcx.is_lang_item(def_id, LangItem::Unsize) {
@@ -232,13 +224,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
     ) -> Result<(), SelectionError<'tcx>> {
         debug!(?stack.obligation);
 
-        // An error type will unify with anything. So, avoid
-        // matching an error type with `ParamCandidate`.
-        // This helps us avoid spurious errors like issue #121941.
-        if stack.obligation.predicate.references_error() {
-            return Ok(());
-        }
-
         let bounds = stack
             .obligation
             .param_env
@@ -565,19 +550,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         obligation: &PolyTraitObligation<'tcx>,
         candidates: &mut SelectionCandidateSet<'tcx>,
     ) {
-        // Essentially any user-written impl will match with an error type,
-        // so creating `ImplCandidates` isn't useful. However, we might
-        // end up finding a candidate elsewhere (e.g. a `BuiltinCandidate` for `Sized`)
-        // This helps us avoid overflow: see issue #72839
-        // Since compilation is already guaranteed to fail, this is just
-        // to try to show the 'nicest' possible errors to the user.
-        // We don't check for errors in the `ParamEnv` - in practice,
-        // it seems to cause us to be overly aggressive in deciding
-        // to give up searching for candidates, leading to spurious errors.
-        if obligation.predicate.references_error() {
-            return;
-        }
-
         let drcx = DeepRejectCtxt::relate_rigid_infer(self.tcx());
         let obligation_args = obligation.predicate.skip_binder().trait_ref.args;
         self.tcx().for_each_relevant_impl(

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -2493,10 +2493,6 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
         let impl_args = self.infcx.fresh_args_for_item(obligation.cause.span, impl_def_id);
 
         let trait_ref = impl_trait_header.trait_ref.instantiate(self.tcx(), impl_args);
-        if trait_ref.references_error() {
-            return Err(());
-        }
-
         debug!(?impl_trait_header);
 
         let Normalized { value: impl_trait_ref, obligations: mut nested_obligations } =

compiler/rustc_ty_utils/src/ty.rs

@@ -6,8 +6,7 @@ use rustc_index::bit_set::BitSet;
 use rustc_middle::bug;
 use rustc_middle::query::Providers;
 use rustc_middle::ty::{
-    self, EarlyBinder, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitableExt,
-    TypeVisitor, Upcast,
+    self, EarlyBinder, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitor, Upcast,
 };
 use rustc_span::DUMMY_SP;
 use rustc_span::def_id::{CRATE_DEF_ID, DefId, LocalDefId};
@@ -95,9 +94,6 @@ fn adt_sized_constraint<'tcx>(
     let tail_ty = tcx.type_of(tail_def.did).instantiate_identity();
 
     let constraint_ty = sized_constraint_for_ty(tcx, tail_ty)?;
-    if let Err(guar) = constraint_ty.error_reported() {
-        return Some(ty::EarlyBinder::bind(Ty::new_error(tcx, guar)));
-    }
 
     // perf hack: if there is a `constraint_ty: Sized` bound, then we know
     // that the type is sized and do not need to check it on the impl.

tests/crashes/124350.rs

@@ -0,0 +1,18 @@
+// regression test for #124350
+
+struct Node<const D: usize> {}
+
+impl<const D: usize> Node<D>
+where
+    SmallVec<{ D * 2 }>:,
+    //~^ ERROR generic parameters may not be used in const operations
+    //~| ERROR constant provided when a type was expected
+{
+    fn new() -> Self {
+        Node::new()
+    }
+}
+
+struct SmallVec<T1>(T1);
+
+fn main() {}