SILGen: Relax assertion about missing vtable entries in a class

lib/SILGen/SILGenType.cpp

@@ -311,8 +311,14 @@ class SILGenVTable : public SILVTableVisitor<SILGenVTable> {
   }
 
   void addPlaceholder(MissingMemberDecl *m) {
-    assert(m->getNumberOfVTableEntries() == 0
-           && "Should not be emitting class with missing members");
+#ifndef NDEBUG
+    auto *classDecl = cast<ClassDecl>(m->getDeclContext());
+    bool isResilient =
+        classDecl->isResilient(SGM.M.getSwiftModule(),
+                               ResilienceExpansion::Maximal);
+    assert(isResilient || m->getNumberOfVTableEntries() == 0 &&
+           "Should not be emitting fragile class with missing members");
+#endif
   }
 };
 

test/SILGen/vtable_implementation_only.swift

@@ -0,0 +1,36 @@
+// RUN: %empty-directory(%t)
+
+// For convenience, this file includes the three different "files" used in this
+// test. It selects one with -DCoreDishwasher, -DDishwasherKit, or neither.
+
+// RUN: %target-swift-frontend -emit-module %s -DCoreDishwasher -module-name CoreDishwasher -o %t/CoreDishwasher -emit-module-path %t/CoreDishwasher.swiftmodule -I %t
+// RUN: %target-swift-frontend -emit-module %s -DDishwasherKit -module-name DishwasherKit -o %t/DishwasherKit -emit-module-path %t/DishwasherKit.swiftmodule -enable-library-evolution -I %t
+// RUN: %target-swift-frontend -emit-silgen -I %t %s
+
+#if CoreDishwasher
+
+  public struct SpimsterWicket {
+    public init() {}
+  }
+
+#elseif DishwasherKit
+
+  @_implementationOnly import CoreDishwasher
+
+  open class Dishwasher {
+    public init() {}
+
+    var wicket = SpimsterWicket()
+
+    open var modelName: String { "Dishwasher" }
+  }
+
+#else
+
+  import DishwasherKit
+
+  open class FancyDishwasher: Dishwasher {
+    open override var modelName: String { "Fancy \(super.modelName)" }
+  }
+
+#endif