[7.x] Fix copyCurentStructure(MapXContentParser) (#76357) (#76374)

* Fix copyCurentStructure(MapXContentParser) (#76357)

This stops `MapXContentParser` from throwing an
`UnsupportedOperationException` when passed as an argument to
`XContentBuilder#copyCurrentStructure`. This is mostly useful in tests
where `Map` is a convenient way to talk about structured configuration
but the production APIs need the map to be embedded into a larger blob
of `XContent`.

Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>

* Fixup

Co-authored-by: Nik Everett <nik9000@gmail.com>
Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>

libs/x-content/src/main/java/org/elasticsearch/common/xcontent/support/MapXContentParser.java

@@ -163,7 +163,7 @@ public Object objectBytes() throws IOException {
 
     @Override
     public boolean hasTextCharacters() {
-        throw new UnsupportedOperationException("use text() instead");
+        return false;
     }
 
     @Override

libs/x-content/src/test/java/org/elasticsearch/common/xcontent/MapXContentParserTests.java

@@ -10,6 +10,7 @@
 
 import org.elasticsearch.core.CheckedConsumer;
 import org.elasticsearch.common.bytes.BytesReference;
+import org.elasticsearch.common.xcontent.json.JsonXContent;
 import org.elasticsearch.common.xcontent.support.MapXContentParser;
 import org.elasticsearch.test.ESTestCase;
 
@@ -57,19 +58,51 @@ public void testSimpleMap() throws IOException {
         });
     }
 
-
     public void testRandomObject() throws IOException {
         compareTokens(builder -> generateRandomObject(builder, randomIntBetween(0, 10)));
     }
 
-    public void compareTokens(CheckedConsumer<XContentBuilder, IOException> consumer) throws IOException {
+    /**
+     * Assert that {@link XContentParser#hasTextCharacters()} returns false because
+     * we don't support {@link XContentParser#textCharacters()}.
+     */
+    public void testHasTextCharacters() throws IOException {
+        assertFalse(
+            new MapXContentParser(
+                xContentRegistry(),
+                LoggingDeprecationHandler.INSTANCE,
+                org.elasticsearch.core.Map.of("a", "b"),
+                randomFrom(XContentType.values())
+            ).hasTextCharacters()
+        );
+    }
+
+    public void testCopyCurrentStructure() throws IOException {
+        try (
+            XContentParser parser = new MapXContentParser(
+                xContentRegistry(),
+                LoggingDeprecationHandler.INSTANCE,
+                org.elasticsearch.core.Map.of("a", "b"),
+                randomFrom(XContentType.values())
+            )
+        ) {
+            try (
+                XContentBuilder builder = JsonXContent.contentBuilder().copyCurrentStructure(parser);
+                XContentParser copied = createParser(builder)
+            ) {
+                assertEquals(copied.map(), org.elasticsearch.core.Map.of("a", "b"));
+            }
+        }
+    }
+
+    private void compareTokens(CheckedConsumer<XContentBuilder, IOException> consumer) throws IOException {
         for (XContentType xContentType : EnumSet.allOf(XContentType.class)) {
             logger.info("--> testing with xcontent type: {}", xContentType);
             compareTokens(consumer, xContentType);
         }
     }
 
-    public void compareTokens(CheckedConsumer<XContentBuilder, IOException> consumer, XContentType xContentType) throws IOException {
+    private void compareTokens(CheckedConsumer<XContentBuilder, IOException> consumer, XContentType xContentType) throws IOException {
         try (XContentBuilder builder = XContentBuilder.builder(xContentType.xContent())) {
             consumer.accept(builder);
             final Map<String, Object> map;