embedded: print an error for class existentials where not all protocols of a composition are class bound

lib/SIL/Utils/InstructionUtils.cpp

@@ -14,6 +14,7 @@
 #include "swift/SIL/InstructionUtils.h"
 #include "swift/SIL/MemAccessUtils.h"
 #include "swift/AST/SubstitutionMap.h"
+#include "swift/AST/ProtocolConformance.h"
 #include "swift/Basic/Assertions.h"
 #include "swift/Basic/Defer.h"
 #include "swift/Basic/NullablePtr.h"
@@ -671,7 +672,20 @@ RuntimeEffect swift::getRuntimeEffect(SILInstruction *inst, SILType &impactType)
            RuntimeEffect::MetaData | RuntimeEffect::Existential;
 
   case SILInstructionKind::InitExistentialRefInst:
-    impactType = inst->getOperand(0)->getType();
+    impactType = cast<InitExistentialRefInst>(inst)->getType();
+    // Make sure to get a diagnostic error in embedded swift for class existentials
+    // where not all protocols of a composition are class bound. For example:
+    //   let existential: any ClassBound & NotClassBound = MyClass()
+    // In future we might support this case and then we can remove this check.
+    for (auto protoRef : cast<InitExistentialRefInst>(inst)->getConformances()) {
+      if (protoRef.isConcrete()) {
+        ProtocolConformance *conf = protoRef.getConcrete();
+        if (isa<NormalProtocolConformance>(conf) &&
+            !conf->getProtocol()->requiresClass()) {
+          return RuntimeEffect::MetaData | RuntimeEffect::Existential;
+        }
+      }
+    }
     return RuntimeEffect::MetaData | RuntimeEffect::ExistentialClassBound;
 
   case SILInstructionKind::InitExistentialMetatypeInst:

test/embedded/existential-composition.swift

@@ -0,0 +1,28 @@
+// RUN: %target-swift-emit-ir -parse-as-library -module-name main -verify %s -enable-experimental-feature Embedded -wmo
+
+// REQUIRES: OS=macosx || OS=linux-gnu
+
+protocol ClassBound: AnyObject {
+  func foo()
+}
+
+protocol OtherProtocol {
+  func bar()
+}
+
+class MyClass: ClassBound, OtherProtocol {
+  func foo() { print("MyClass.foo()") }
+  func bar() { print("MyClass.bar()") }
+}
+
+// Currently we don't support this
+func test(existential: any ClassBound & OtherProtocol) {
+}
+
+@main
+struct Main {
+  static func main() {
+    test(existential: MyClass()) // expected-error {{cannot use a value of protocol type 'any ClassBound & OtherProtocol' in embedded Swift}}
+                                 // expected-note@-4 {{called from here}}
+  }
+}