Fix #3122

release-notes/CREDITS-2.x

@@ -1327,3 +1327,7 @@ Asaf Romano (asaf-romano@github)
 David Hoffman (dhofftgt@github)
   * Contributed #3082: Dont track unknown props in buffer if `ignoreAllUnknown` is true
    (2.13.0)
+
+Eric Sirianni (sirianni@github)
+  * Reported #3122: Deep merge for `JsonNode` using `ObjectReader.readTree()`
+   (2.13.0)

release-notes/VERSION-2.x

@@ -28,6 +28,8 @@ Project: jackson-databind
 #3099: Optimize "AnnotatedConstructor.call()" case by passing explicit null
 #3101: Add AnnotationIntrospector.XmlExtensions interface for decoupling javax dependencies
 #3117: Use more limiting default visibility settings for JDK types (java.*, javax.*)
+#3122: Deep merge for `JsonNode` using `ObjectReader.readTree()`
+ (reported by Eric S)
 - Fix to avoid problem with `BigDecimalNode`, scale of `Integer.MIN_VALUE` (see
   [dataformats-binary#264] for details)
 

src/main/java/com/fasterxml/jackson/databind/ObjectReader.java

@@ -2062,6 +2062,12 @@ protected final JsonNode _bindAndCloseAsTree(JsonParser p0) throws IOException {
 
     protected final JsonNode _bindAsTree(JsonParser p) throws IOException
     {
+        // 16-Apr-2021, tatu: Should usually NOT be called this way but
+        //    as per [databind#3122] should still work
+        if (_valueToUpdate != null) {
+            return (JsonNode) _bind(p, _valueToUpdate);
+        }
+
         // Need to inline `_initForReading()` due to tree reading handling end-of-input specially
         _config.initialize(p);
         if (_schema != null) {
@@ -2098,6 +2104,13 @@ protected final JsonNode _bindAsTree(JsonParser p) throws IOException
      */
     protected final JsonNode _bindAsTreeOrNull(JsonParser p) throws IOException
     {
+        // 16-Apr-2021, tatu: Should usually NOT be called this way but
+        //    as per [databind#3122] should still work
+        if (_valueToUpdate != null) {
+            return (JsonNode) _bind(p, _valueToUpdate);
+        }
+
+        // Need to inline `_initForReading()` (as per above)
         _config.initialize(p);
         if (_schema != null) {
             p.setSchema(_schema);

src/test/java/com/fasterxml/jackson/databind/deser/merge/NodeMergeTest.java

@@ -1,7 +1,7 @@
 package com.fasterxml.jackson.databind.deser.merge;
 
 import com.fasterxml.jackson.annotation.JsonMerge;
-
+import com.fasterxml.jackson.core.JsonParser;
 import com.fasterxml.jackson.databind.*;
 import com.fasterxml.jackson.databind.node.ObjectNode;
 import com.fasterxml.jackson.databind.node.ArrayNode;
@@ -162,4 +162,38 @@ public void testUpdateArrayWithString() throws Exception
 
         assertEquals(a2q("{'test':'n/a'}"), result.toString());
     }
+
+    // [databind#3122]: "readTree()" fails where "readValue()" doesn't:
+    public void testObjectDeepMerge3122() throws Exception
+    {
+        final String jsonToMerge = a2q("{'root':{'b':'bbb','foo':'goodbye'}}");
+
+        JsonNode node1 = MAPPER.readTree(a2q("{'root':{'a':'aaa','foo':'hello'}}"));
+        assertEquals(2, node1.path("root").size());
+
+        JsonNode node2 = MAPPER.readerForUpdating(node1)
+                .readValue(jsonToMerge);
+        assertSame(node1, node2);
+        assertEquals(3, node1.path("root").size());
+
+        node1 = MAPPER.readTree(a2q("{'root':{'a':'aaa','foo':'hello'}}"));
+        JsonNode node3 = MAPPER.readerForUpdating(node1)
+                .readTree(jsonToMerge);
+        assertSame(node1, node3);
+        assertEquals(3, node1.path("root").size());
+
+        node1 = MAPPER.readTree(a2q("{'root':{'a':'aaa','foo':'hello'}}"));
+        JsonNode node4 = MAPPER.readerForUpdating(node1)
+                .readTree(utf8Bytes(jsonToMerge));
+        assertSame(node1, node4);
+        assertEquals(3, node1.path("root").size());
+
+        // And finally variant passing `JsonParser`
+        try (JsonParser p = MAPPER.createParser(jsonToMerge)) {
+            JsonNode node5 = MAPPER.readerForUpdating(node1)
+                    .readTree(p);
+            assertSame(node1, node5);
+            assertEquals(3, node1.path("root").size());
+        }
+    }
 }