[Interop][SwiftToCxx] emit helper cases class in C++ for Swift enum

Author: WANGJIEKE

lib/PrintAsClang/DeclAndTypePrinter.cpp

@@ -392,8 +392,20 @@ class DeclAndTypePrinter::Implementation
       ClangValueTypePrinter printer(os, owningPrinter.prologueOS,
                                     owningPrinter.typeMapping,
                                     owningPrinter.interopContext);
-      printer.printValueTypeDecl(
-          ED, /*bodyPrinter=*/[&]() {}); // TODO: (tongjie) print cases
+      printer.printValueTypeDecl(ED, /*bodyPrinter=*/[&]() {
+        ClangSyntaxPrinter syntaxPrinter(os);
+        os << "  enum class cases { ";
+        llvm::interleaveComma(
+            ED->getAllCases(), os, [&](const EnumCaseDecl *caseDecl) {
+              llvm::interleaveComma(
+                  caseDecl->getElements(), os,
+                  [&](const EnumElementDecl *elementDecl) {
+                    syntaxPrinter.printIdentifier(
+                        elementDecl->getBaseIdentifier().str());
+                  });
+            });
+        os << " };\n";
+      });
       os << outOfLineDefinitions;
       outOfLineDefinitions.clear();
       return;

test/Interop/SwiftToCxx/enums/swift-enum-cases-in-cxx.swift

@@ -0,0 +1,34 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend %s -typecheck -module-name Enums -clang-header-expose-public-decls -emit-clang-header-path %t/enums.h
+// RUN: %FileCheck %s < %t/enums.h
+
+// RUN: %check-interop-cxx-header-in-clang(%t/enums.h -Wno-unused-private-field -Wno-unused-function)
+
+public enum EnumMultipleElementsInSingleCase { case first, second }
+
+public enum EnumSingleElementInSingleCase {
+    case first
+    case second
+}
+
+public enum EnumCaseIsSwiftKeyword {
+    case first(a: Int)
+    case `protocol`(b: Double)
+}
+
+public enum EnumCaseIsCxxKeyword {
+    case first, second(x: Float)
+    case const
+}
+
+// CHECK: class EnumCaseIsCxxKeyword final {
+// CHECK: enum class cases { first, second, const_ };
+
+// CHECK: class EnumCaseIsSwiftKeyword final {
+// CHECK: enum class cases { first, protocol };
+
+// CHECK: class EnumMultipleElementsInSingleCase final {
+// CHECK: enum class cases { first, second };
+
+// CHECK: class EnumSingleElementInSingleCase final {
+// CHECK: enum class cases { first, second };