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Author: eholk

compiler/rustc_mir_transform/src/generator.rs

@@ -749,15 +749,20 @@ fn sanitize_witness<'tcx>(
         }
         let decl_ty = tcx.normalize_erasing_regions(param_env, decl.ty);
 
-        let is_uninhabited = tcx.is_ty_uninhabited_from(
+        let is_inhabited = !tcx.is_ty_uninhabited_from(
             tcx.parent_module(tcx.hir().local_def_id_to_hir_id(did.expect_local())).to_def_id(),
             decl_ty,
             param_env,
         );
 
         // Sanity check that typeck knows about the type of locals which are
         // live across a suspension point
-        if !is_uninhabited && !allowed.contains(&decl_ty) && !allowed_upvars.contains(&decl_ty) {
+        if is_inhabited || allowed.contains(&decl_ty) || allowed_upvars.contains(&decl_ty) {
+            // This type which appears in the generator either...
+            // - is uninhabited, in which case it can't actually be captured at runtime
+            // - appears in the approximation from the static type (`allowed`)
+            // - appears in the list of upvars ...
+        } else {
             span_bug!(
                 body.span,
                 "Broken MIR: generator contains type {} in MIR, \