Fix #3220

Author: cowtowncoder

release-notes/CREDITS-2.x

@@ -974,6 +974,9 @@ Marcos Passos (marcospassos@github(
    (2.10.0)
   * Reported #2795: Cannot detect creator arguments of mixins for JDK types
    (2.11.3)
+  * Reported #3220: (regression) Factory method generic type resolution does not use
+    Class-bound type parameter
+   (2.12.5)
 
 David Becker (dsbecker@github)
   * Suggested #2433: Improve `NullNode.equals()`

release-notes/VERSION-2.x

@@ -4,6 +4,12 @@ Project: jackson-databind
 === Releases === 
 ------------------------------------------------------------------------
 
+2.12.5 (not yet released)
+
+#3220: (regression) Factory method generic type resolution does not use
+  Class-bound type parameter
+ (reported by Marcos P)
+
 2.12.4 (06-Jul-2021)
 
 #3139: Deserialization of "empty" subtype with DEDUCTION failed

src/main/java/com/fasterxml/jackson/databind/introspect/AnnotatedCreatorCollector.java

@@ -219,10 +219,14 @@ private List<AnnotatedMethod> _findPotentialFactories(TypeFactory typeFactory,
         // 27-Oct-2020, tatu: SIGH. As per [databind#2894] there is widespread use of
         //   incorrect bindings in the wild -- not supported (no tests) but used
         //   nonetheless. So, for 2.11.x, put back "Bad Bindings"...
-//        final TypeResolutionContext typeResCtxt = _typeContext;
+//        
 
         // 03-Nov-2020, ckozak: Implement generic JsonCreator TypeVariable handling [databind#2895]
-        final TypeResolutionContext emptyTypeResCtxt = new TypeResolutionContext.Empty(typeFactory);
+//        final TypeResolutionContext emptyTypeResCtxt = new TypeResolutionContext.Empty(typeFactory);
+
+        // 23-Aug-2021, tatu: Double-d'oh! As per [databind#3220], we must revert to
+        //   the Incorrect Illogical But Used By Users Bindings... for 2.x at least.
+        final TypeResolutionContext initialTypeResCtxt = _typeContext;
 
         int factoryCount = candidates.size();
         List<AnnotatedMethod> result = new ArrayList<>(factoryCount);
@@ -247,7 +251,7 @@ private List<AnnotatedMethod> _findPotentialFactories(TypeFactory typeFactory,
                     if (key.equals(methodKeys[i])) {
                         result.set(i,
                                 constructFactoryCreator(candidates.get(i),
-                                        emptyTypeResCtxt, mixinFactory));
+                                        initialTypeResCtxt, mixinFactory));
                         break;
                     }
                 }
@@ -261,8 +265,9 @@ private List<AnnotatedMethod> _findPotentialFactories(TypeFactory typeFactory,
                 // 06-Nov-2020, tatu: Fix from [databind#2895] will try to resolve
                 //   nominal static method type bindings into expected target type
                 //   (if generic types involved)
+                // 23-Aug-2021, tatu: ... is this still needed, wrt un-fix in [databind#3220]?
                 TypeResolutionContext typeResCtxt = MethodGenericTypeResolver.narrowMethodTypeParameters(
-                        candidate, type, typeFactory, emptyTypeResCtxt);
+                        candidate, type, typeFactory, initialTypeResCtxt);
                 result.set(i,
                         constructFactoryCreator(candidate, typeResCtxt, null));
             }

src/test/java/com/fasterxml/jackson/failing/MixinForFactoryMethod3220Test.java renamed to src/test/java/com/fasterxml/jackson/databind/mixins/MixinForFactoryMethod3220Test.java

@@ -1,4 +1,4 @@
-package com.fasterxml.jackson.failing;
+package com.fasterxml.jackson.databind.mixins;
 
 import java.util.Objects;
 
@@ -8,6 +8,17 @@
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.json.JsonMapper;
 
+// 23-Aug-2021, tatu: UGGGGH. This is a recurring problem; users assuming
+//   that a generic type parameter T (or whatever) of a Class will be related
+//   to locally declared type parameter with same name (T), assume Creator
+//   factory method will magically work. Despite Java Language quite clearly
+//   considering these separate bindings regardless of name overlap.
+//
+//   But for Jackson 2.x there is common enough usage of this anti-patterns so
+//   we cannot block it.
+//
+//   NOTE! Problem is actually not the mixin handling but type resolution;
+//   see f.ex [databind#2821], [databind#2895]
 public class MixinForFactoryMethod3220Test
     extends BaseMapTest
 {
@@ -125,7 +136,7 @@ public int hashCode() {
     }
 
     // [databind#3220]
-    public void testMixin() throws Exception
+    public void testMixin3220() throws Exception
     {
         ObjectMapper mapper = JsonMapper.builder()
                 .addMixIn(Timestamped.class, TimestampedMixin.class)