Backport #2220 fix

Author: cowtowncoder

release-notes/VERSION-2.x

@@ -24,6 +24,7 @@ Project: jackson-databind
 #2211: Change of behavior (2.8 -> 2.9) with `ObjectMapper.readTree(input)` with no content
 #2217: Suboptimal memory allocation in `TextNode.getBinaryValue()`
  (reported by Christoph B)
+#2220: Force serialization always for `convertValue()`; avoid short-cuts
 #2223: Add `missingNode()` method in `JsonNodeFactory`
 #2227: Minor cleanup of exception message for `Enum` binding failure
  (reported by RightHandedMonkey@github)

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

@@ -33,7 +33,13 @@ public enum DeserializationFeature implements ConfigFeature
      * or {@link java.util.Collection} context) is available.
      * If enabled such values will be deserialized as {@link java.math.BigDecimal}s;
      * if disabled, will be deserialized as {@link Double}s.
-     * <p>
+     *<p>
+     * NOTE: one aspect of {@link java.math.BigDecimal} handling that may need
+     * configuring is whether trailing zeroes are trimmed:
+     * {@link com.fasterxml.jackson.databind.node.JsonNodeFactory} has
+     * {@link com.fasterxml.jackson.databind.node.JsonNodeFactory#withExactBigDecimals} for
+     * changing default behavior (default is for trailing zeroes to be trimmed).
+     *<p>
      * Feature is disabled by default, meaning that "untyped" floating
      * point numbers will by default be deserialized as {@link Double}s
      * (choice is for performance reason -- BigDecimals are slower than

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

@@ -2688,9 +2688,10 @@ public <T> T treeToValue(TreeNode n, Class<T> valueType)
         throws JsonProcessingException
     {
         try {
+            // 25-Jan-2019, tatu: [databind#2220] won't prevent existing coercions here
             // Simple cast when we just want to cast to, say, ObjectNode
-            // ... one caveat; while everything is Object.class, let's not take shortcut
-            if (valueType != Object.class && valueType.isAssignableFrom(n.getClass())) {
+            if (TreeNode.class.isAssignableFrom(valueType)
+                    && valueType.isAssignableFrom(n.getClass())) {
                 return (T) n;
             }
             // 20-Apr-2016, tatu: Another thing: for VALUE_EMBEDDED_OBJECT, assume similar
@@ -3648,20 +3649,7 @@ public <T> T convertValue(Object fromValue, JavaType toValueType)
     protected Object _convert(Object fromValue, JavaType toValueType)
         throws IllegalArgumentException
     {
-        // [databind#1433] Do not shortcut null values.
-        // This defaults primitives and fires deserializer getNullValue hooks.
-        if (fromValue != null) {
-            // also, as per [databind#11], consider case for simple cast
-            // But with caveats: one is that while everything is Object.class, we don't
-            // want to "optimize" that out; and the other is that we also do not want
-            // to lose conversions of generic types.
-            Class<?> targetType = toValueType.getRawClass();
-            if (targetType != Object.class
-                    && !toValueType.hasGenericTypes()
-                    && targetType.isAssignableFrom(fromValue.getClass())) {
-                return fromValue;
-            }
-        }
+        // 25-Jan-2019, tatu: [databind#2220] Let's NOT try to short-circuit anything
 
         // Then use TokenBuffer, which is a JsonGenerator:
         TokenBuffer buf = new TokenBuffer(this, false);

src/test/java/com/fasterxml/jackson/databind/convert/TestBeanConversions.java

@@ -217,19 +217,10 @@ private void _convertAndVerifyPoint(ObjectMapper m)
      */
     public void testIssue11() throws Exception
     {
-        // First the expected use case, Node specification
-        ObjectNode root = MAPPER.createObjectNode();
-        JsonNode n = root;
-        ObjectNode ob2 = MAPPER.convertValue(n, ObjectNode.class);
-        assertSame(root, ob2);
-
-        JsonNode n2 = MAPPER.convertValue(n, JsonNode.class);
-        assertSame(root, n2);
-        
         // then some other no-op conversions
-        String STR = "test";
-        CharSequence seq = MAPPER.convertValue(STR, CharSequence.class);
-        assertSame(STR, seq);
+        StringBuilder SB = new StringBuilder("test");
+        CharSequence seq = MAPPER.convertValue(SB, CharSequence.class);
+        assertNotSame(SB, seq);
 
         // and then something that should NOT use short-cut
         Leaf l = new Leaf(13);