Do not abort compilation when failing to normalize opaque types.

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

@@ -101,6 +101,18 @@ pub trait InferCtxtExt<'tcx> {
 }
 
 pub trait TypeErrCtxtExt<'tcx> {
+    fn build_overflow_error<T>(
+        &self,
+        predicate: &T,
+        span: Span,
+        suggest_increasing_limit: bool,
+    ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>
+    where
+        T: fmt::Display
+            + TypeFoldable<'tcx>
+            + Print<'tcx, FmtPrinter<'tcx, 'tcx>, Output = FmtPrinter<'tcx, 'tcx>>,
+        <T as Print<'tcx, FmtPrinter<'tcx, 'tcx>>>::Error: std::fmt::Debug;
+
     fn report_overflow_error<T>(
         &self,
         predicate: &T,
@@ -478,6 +490,26 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         suggest_increasing_limit: bool,
         mutate: impl FnOnce(&mut Diagnostic),
     ) -> !
+    where
+        T: fmt::Display
+            + TypeFoldable<'tcx>
+            + Print<'tcx, FmtPrinter<'tcx, 'tcx>, Output = FmtPrinter<'tcx, 'tcx>>,
+        <T as Print<'tcx, FmtPrinter<'tcx, 'tcx>>>::Error: std::fmt::Debug,
+    {
+        let mut err = self.build_overflow_error(predicate, span, suggest_increasing_limit);
+        mutate(&mut err);
+        err.emit();
+
+        self.tcx.sess.abort_if_errors();
+        bug!();
+    }
+
+    fn build_overflow_error<T>(
+        &self,
+        predicate: &T,
+        span: Span,
+        suggest_increasing_limit: bool,
+    ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>
     where
         T: fmt::Display
             + TypeFoldable<'tcx>
@@ -511,11 +543,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             self.suggest_new_overflow_limit(&mut err);
         }
 
-        mutate(&mut err);
-
-        err.emit();
-        self.tcx.sess.abort_if_errors();
-        bug!();
+        err
     }
 
     /// Reports that an overflow has occurred and halts compilation. We

compiler/rustc_trait_selection/src/traits/query/normalize.rs

@@ -216,12 +216,16 @@ impl<'cx, 'tcx> FallibleTypeFolder<'tcx> for QueryNormalizer<'cx, 'tcx> {
                         let substs = substs.try_fold_with(self)?;
                         let recursion_limit = self.tcx().recursion_limit();
                         if !recursion_limit.value_within_limit(self.anon_depth) {
-                            self.infcx.err_ctxt().report_overflow_error(
-                                &ty,
-                                self.cause.span,
-                                true,
-                                |_| {},
-                            );
+                            // A closure or generator may have itself as in its upvars.  This
+                            // should be checked handled by the recursion check for opaque types,
+                            // but we may end up here before that check can happen.  In that case,
+                            // we delay a bug to mark the trip, and continue without revealing the
+                            // opaque.
+                            self.infcx
+                                .err_ctxt()
+                                .build_overflow_error(&ty, self.cause.span, true)
+                                .delay_as_bug();
+                            return ty.try_super_fold_with(self);
                         }
 
                         let generic_ty = self.tcx().bound_type_of(def_id);