core: fix "null" enum field

jadx-core/src/main/java/jadx/core/dex/instructions/args/RegisterArg.java

 package jadx.core.dex.instructions.args;
 
+import jadx.core.dex.attributes.AttributeType;
+import jadx.core.dex.info.FieldInfo;
 import jadx.core.dex.instructions.ConstClassNode;
 import jadx.core.dex.instructions.ConstStringNode;
+import jadx.core.dex.instructions.IndexInsnNode;
 import jadx.core.dex.instructions.InsnType;
+import jadx.core.dex.nodes.DexNode;
+import jadx.core.dex.nodes.FieldNode;
 import jadx.core.dex.nodes.InsnNode;
+import jadx.core.dex.nodes.parser.FieldValueAttr;
 import jadx.core.dex.visitors.InstructionRemover;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 public class RegisterArg extends InsnArg {
+	private static final Logger LOG = LoggerFactory.getLogger(RegisterArg.class);
+
 	protected final int regNum;
 
 	public RegisterArg(int rn) {
@@ -45,7 +56,7 @@ public class RegisterArg extends InsnArg {
 	 *
 	 * @return LiteralArg, String or ArgType
 	 */
-	public Object getConstValue() {
+	public Object getConstValue(DexNode dex) {
 		InsnNode parInsn = getAssignInsn();
 		if (parInsn != null) {
 			InsnType insnType = parInsn.getType();
@@ -56,6 +67,18 @@ public class RegisterArg extends InsnArg {
 					return ((ConstStringNode) parInsn).getString();
 				case CONST_CLASS:
 					return ((ConstClassNode) parInsn).getClsType();
+				case SGET:
+					FieldInfo f = (FieldInfo) ((IndexInsnNode) parInsn).getIndex();
+					FieldNode fieldNode = dex.resolveField(f);
+					if (fieldNode != null) {
+						FieldValueAttr attr = (FieldValueAttr) fieldNode.getAttributes().get(AttributeType.FIELD_VALUE);
+						if (attr != null) {
+							return attr.getValue();
+						}
+					} else {
+						LOG.warn("Field {} not found in dex {}", f, dex);
+					}
+					break;
 			}
 		}
 		return null;

jadx-core/src/main/java/jadx/core/dex/nodes/DexNode.java

 package jadx.core.dex.nodes;
 
 import jadx.core.dex.info.ClassInfo;
+import jadx.core.dex.info.FieldInfo;
 import jadx.core.dex.info.MethodInfo;
 import jadx.core.dex.instructions.args.ArgType;
 import jadx.core.utils.exceptions.DecodeException;
@@ -64,6 +65,14 @@ public class DexNode {
 		return null;
 	}
 
+	public FieldNode resolveField(FieldInfo field) {
+		ClassNode cls = resolveClass(field.getDeclClass());
+		if (cls != null) {
+			return cls.searchField(field);
+		}
+		return null;
+	}
+
 	public Map<Object, FieldNode> getConstFields() {
 		return constFields;
 	}

jadx-core/src/main/java/jadx/core/dex/visitors/EnumVisitor.java

@@ -117,7 +117,10 @@ public class EnumVisitor extends AbstractVisitor {
 				RegisterArg nameArg = (RegisterArg) insn.getArg(0);
 				// InsnArg pos = insn.getArg(1);
 				// TODO add check: pos == j
-				String name = (String) nameArg.getConstValue();
+				String name = (String) nameArg.getConstValue(cls.dex());
+				if (name == null) {
+					throw new JadxException("Unknown enum field name: " + cls);
+				}
 
 				EnumField field = new EnumField(name, insn.getArgsCount() - 2);
 				attr.getFields().add(field);

jadx-samples/src/main/java/jadx/samples/TestEnum.java

@@ -11,6 +11,12 @@ public class TestEnum extends AbstractTest {
 		NORTH, SOUTH, EAST, WEST
 	}
 
+	public static final String DOG = "DOG";
+
+	public enum Animal {
+		CAT, DOG
+	}
+
 	private static int three = 3;
 
 	public enum Numbers {