Expose getStrings() option on JsonReader.Options (#1180)

* Expose getStrings() option on JsonReader.Options

Resolves #1173

* Fix clone

Co-authored-by: Jake Wharton <github@jakewharton.com>

* Add mutation check

* Use set and make it unmodifiable

* Back to list

* strings()

* No clone()

Co-authored-by: Jake Wharton <github@jakewharton.com>

moshi/src/main/java/com/squareup/moshi/JsonReader.java

@@ -27,6 +27,8 @@ import okio.Buffer;
 import okio.BufferedSource;
 import okio.ByteString;
 
+import static java.util.Collections.unmodifiableList;
+
 /**
  * Reads a JSON (<a href="http://www.ietf.org/rfc/rfc7159.txt">RFC 7159</a>)
  * encoded value as a stream of tokens. This stream includes both literal
@@ -528,6 +530,11 @@ public abstract class JsonReader implements Closeable {
       this.doubleQuoteSuffix = doubleQuoteSuffix;
     }
 
+    /** Returns a copy of this {@link Options Option's} strings. */
+    public List<String> strings() {
+      return unmodifiableList(Arrays.asList(strings));
+    }
+
     @CheckReturnValue public static Options of(String... strings) {
       try {
         ByteString[] result = new ByteString[strings.length];

moshi/src/test/java/com/squareup/moshi/JsonReaderTest.java

@@ -20,6 +20,7 @@ import java.io.IOException;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
+import java.util.Set;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.junit.runners.Parameterized;
@@ -1157,6 +1158,20 @@ public final class JsonReaderTest {
     reader.endObject();
   }
 
+  @Test public void optionsStrings() {
+    String[] options = new String[] { "a", "b", "c" };
+    JsonReader.Options abc = JsonReader.Options.of("a", "b", "c");
+    List<String> strings = abc.strings();
+    assertThat(options).containsExactlyElementsOf(strings);
+    try {
+      // Confirm it's unmodifiable and we can't mutate the original underlying array
+      strings.add("d");
+      fail();
+    } catch (UnsupportedOperationException expected) {
+
+    }
+  }
+
   /** Peek a value, then read it, recursively. */
   private void readValue(JsonReader reader, boolean peekJsonFirst) throws IOException {
     JsonReader.Token token = reader.peek();