Fix #2034

Author: cowtowncoder

release-notes/CREDITS-2.x

@@ -788,3 +788,7 @@ Jakub Skierbiszewski (jskierbi@github)
 Carter Kozak (cakofony@github)
   * Reported #2016: Delegating JsonCreator disregards JsonDeserialize info
    (2.9.6)
+
+Reinhard Prechtl (dnno@github)
+  * Reported #2034: Serialization problem with type specialization of nested generic types
+   (2.9.6)

release-notes/VERSION-2.x

@@ -35,6 +35,8 @@ Project: jackson-databind
  (reported by franboragina@github)
 #2032: Blacklist another serialization gadget (ibatis)
  (reported by Guixiong Wu)
+#2034: Serialization problem with type specialization of nested generic types
+ (reported by Reinhard P)
 
 2.9.5 (26-Mar-2018)
 

src/main/java/com/fasterxml/jackson/databind/type/TypeFactory.java

@@ -455,6 +455,12 @@ private String _resolveTypePlaceholders(JavaType sourceType, JavaType actualType
             JavaType exp = expectedTypes.get(i);
             JavaType act = actualTypes.get(i);
             if (!_verifyAndResolvePlaceholders(exp, act)) {
+                // 14-May-2018, tatu: As per [databind#2034] it seems we better relax assignment
+                //   rules further -- at least likely "raw" (untyped, non-generic) base should probably
+                //   allow specialization.
+                if (exp.hasRawClass(Object.class)) {
+                    continue;
+                }
                 // 19-Apr-2018, tatu: Hack for [databind#1964] -- allow type demotion
                 //    for `java.util.Map` key type if (and only if) target type is
                 //    `java.lang.Object`

src/test/java/com/fasterxml/jackson/databind/jsontype/SubTypeResolution1964Test.java

@@ -2,6 +2,7 @@
 
 import java.util.*;
 
+import com.fasterxml.jackson.annotation.JsonProperty;
 import com.fasterxml.jackson.databind.*;
 
 /**
@@ -15,6 +16,7 @@
 @SuppressWarnings("serial")
 public class SubTypeResolution1964Test extends BaseMapTest
 {
+    // [databind#1964]
     static class AccessModel {
         private Map<String, Collection<String>> repositoryPrivileges;
 
@@ -32,9 +34,47 @@ public void setRepositoryPrivileges(Map<String, Collection<String>> repositoryPr
             this.repositoryPrivileges = repositoryPrivileges;
         }
     }
-
     static class CustomMap<T> extends LinkedHashMap<Object, T> { }
 
+    // [databind#2034]: specialization from `Object` to other types probably should
+    // just be allowed (at least in serialization case)
+    interface Dummy {
+      List<String> getStrings();
+    }
+
+    static class MetaModel<M, B> extends AbstractMetaValue<M, M, B> {
+
+        @JsonProperty
+        protected final Map<String, AbstractMetaValue<M, ?, B>> attributes = new HashMap<>();
+
+        public <V> ListMetaAttribute<M, V, B> describeList(final String attributeName) {
+          final ListMetaAttribute<M, V, B> metaAttribute = new ListMetaAttribute<>();
+          attributes.put(attributeName, metaAttribute);
+          return metaAttribute;
+        }
+      }
+
+    static abstract class AbstractMetaValue<M, V, B> {
+        public int getBogus() { return 3; }
+    }
+
+    static class ListMetaAttribute<M, V, B> extends MetaAttribute<M, List<V>, B> {
+        public ListMetaAttribute() { }
+    }
+
+    static class MetaAttribute<M, V, B> extends AbstractMetaValue<M, V, B> {
+        public MetaAttribute() { }
+      }
+    
+    /*
+    /**********************************************************************
+    /* Unit tests
+    /**********************************************************************
+     */
+
+    final ObjectMapper MAPPER = newObjectMapper();
+
+    // [databind#1964]
     public void testTypeCompatibility1964() throws Exception
     {
         // Important! Must use raw type since assignment requires effectively
@@ -49,8 +89,17 @@ public void testTypeCompatibility1964() throws Exception
         AccessModel accessModel = new AccessModel();
         accessModel.setRepositoryPrivileges(repoPrivilegesMap);
 
-        ObjectMapper mapper = new ObjectMapper();
-        String jsonStr = mapper.writeValueAsString(accessModel);
+        String jsonStr = MAPPER.writeValueAsString(accessModel);
+        // ... could/should verify more, perhaps, but for now let it be.
+        assertNotNull(jsonStr);
+    }
+
+    // [databind#2034]
+    public void testTypeSpecialization2034() throws Exception
+    {
+        MetaModel<Dummy, Dummy> metaModel = new MetaModel<>();
+        metaModel.describeList("a1");
+        String jsonStr = MAPPER.writeValueAsString(metaModel);
         // ... could/should verify more, perhaps, but for now let it be.
         assertNotNull(jsonStr);
     }

src/test/java/com/fasterxml/jackson/databind/jsontype/TestScalars.java

@@ -42,14 +42,14 @@ public ScalarList add(Object v) {
             return this;
         }
     }
-    
+
     /*
     /**********************************************************
     /* Unit tests
     /**********************************************************
      */
 
-    final ObjectMapper MAPPER = new ObjectMapper();
+    final ObjectMapper MAPPER = newObjectMapper();
 
     /**
      * Ensure that per-property dynamic types work, both for "native" types