Fixes #4584: add AnnotationIntrospector method for canonical Creator discovery

Author: cowtowncoder

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

@@ -1397,6 +1397,38 @@ public JsonCreator.Mode findCreatorAnnotation(MapperConfig<?> config, Annotated
         return null;
     }
 
+    /**
+     * Method called to check if introspector is able to detect so-called Canonical
+     * creator: primary Creator to use when no explicit annotation found
+     * (via {@link #findCreatorAnnotation}).
+     * This is the case for example for Java Record types (but for which handling
+     * is in-built); but is specifically true for various "Data" classes by frameworks like
+     * Lombok and JVM languages like Kotlin and Scala (case classes).
+     * If introspector can determine that one of given {@link PotentialCreator}s should
+     * be considered canonical, it should return it; if not, should return {@code null}.
+     *<p>
+     * NOTE: when returning chosen Creator, it may be necessary to mark its "mode"
+     * with {@link PotentialCreator#overrideMode} (especially for "delegating" creators).
+     *<p>
+     * NOTE: method is NOT called for Java Record types.
+     *
+     * @param config Configuration settings in effect (for deserialization)
+     * @param valueClass Class being instantiated and defines Creators passed
+     * @param declaredConstructors Constructors value class declares
+     * @param declaredFactories Factory methods value class declares
+     *
+     * @return The one Canonical Creator to use for {@code valueClass}, if it can be
+     *    determined; {@code null} if not.
+     *
+     * @since 2.18
+     */
+    public PotentialCreator findCanonicalCreator(MapperConfig<?> config,
+            AnnotatedClass valueClass,
+            List<PotentialCreator> declaredConstructors,
+            List<PotentialCreator> declaredFactories) {
+        return null;
+    }
+
     /**
      * Method for checking whether given annotated item (method, constructor)
      * has an annotation

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

@@ -735,9 +735,23 @@ public JsonCreator.Mode findCreatorAnnotation(MapperConfig<?> config, Annotated
         return (mode == null) ? _secondary.findCreatorAnnotation(config, a) : mode;
     }
 
+    @Override
+    public PotentialCreator findCanonicalCreator(MapperConfig<?> config,
+            AnnotatedClass valueClass,
+            List<PotentialCreator> declaredConstructors,
+            List<PotentialCreator> declaredFactories) {
+        PotentialCreator canonical = _primary.findCanonicalCreator(config,
+                valueClass, declaredConstructors, declaredFactories);
+        if (canonical == null) {
+            canonical = _secondary.findCanonicalCreator(config,
+                    valueClass, declaredConstructors, declaredFactories);
+        }
+        return canonical;
+    }
+    
     /*
     /**********************************************************************
-    /* Deserialization: other method annotations
+    /* Deserialization: other property annotations
     /**********************************************************************
      */
 

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

@@ -655,15 +655,15 @@ protected void _addCreators(Map<String, POJOPropertyBuilder> props)
         if (_isRecordType) {
             canonical = JDK14Util.findCanonicalRecordConstructor(_config, _classDef, constructors);
         } else {
-            // !!! TODO: fetch Canonical for Kotlin, Scala, via AnnotationIntrospector?
-            canonical = null;
+            canonical = _annotationIntrospector.findCanonicalCreator(_config, _classDef,
+                    constructors, factories);
         }
 
         // Next: remove creators marked as explicitly disabled
         _removeDisabledCreators(constructors);
         _removeDisabledCreators(factories);
         // And then remove non-annotated static methods that do not look like factories
-        _removeNonFactoryStaticMethods(factories);
+        _removeNonFactoryStaticMethods(factories, canonical);
 
         // and use annotations to find explicitly chosen Creators
         if (_useAnnotations) { // can't have explicit ones without Annotation introspection
@@ -682,12 +682,12 @@ protected void _addCreators(Map<String, POJOPropertyBuilder> props)
         }
 
         // But if no annotation-based Creators found, find/use canonical Creator
-        // (JDK 17 Record/Scala/Kotlin)
+        // (Scala/Kotlin/Lombok?)
         if (!creators.hasPropertiesBased()) {
-            // for Records:
             if (canonical != null) {
                 // ... but only process if still included as a candidate
-                if (constructors.remove(canonical)) {
+                if (constructors.remove(canonical)
+                        || factories.remove(canonical)) {
                     // But wait! Could be delegating
                     if (_isDelegatingConstructor(canonical)) {
                         creators.addExplicitDelegating(canonical);
@@ -733,6 +733,16 @@ protected void _addCreators(Map<String, POJOPropertyBuilder> props)
     // looks like delegating one
     private boolean _isDelegatingConstructor(PotentialCreator ctor)
     {
+        // First things first: could be 
+        switch (ctor.creatorMode()) {
+        case DELEGATING:
+            return true;
+        case DISABLED:
+        case PROPERTIES:
+            return false;
+        default:
+        }
+
         // Only consider single-arg case, for now
         if (ctor.paramCount() == 1) {
             // Main thing: @JsonValue makes it delegating:
@@ -779,7 +789,8 @@ private void _removeNonVisibleCreators(List<PotentialCreator> ctors)
         }
     }
 
-    private void _removeNonFactoryStaticMethods(List<PotentialCreator> ctors)
+    private void _removeNonFactoryStaticMethods(List<PotentialCreator> ctors,
+            PotentialCreator canonical)
     {
         final Class<?> rawType = _type.getRawClass();
         Iterator<PotentialCreator> it = ctors.iterator();
@@ -789,6 +800,10 @@ private void _removeNonFactoryStaticMethods(List<PotentialCreator> ctors)
             if (ctor.creatorMode() != null) {
                 continue;
             }
+            // Do not trim canonical either
+            if (canonical == ctor) {
+                continue;
+            }
             // Copied from `BasicBeanDescription.isFactoryMethod()`
             AnnotatedWithParams factory = ctor.creator();
             if (rawType.isAssignableFrom(factory.getRawType())

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

@@ -19,7 +19,7 @@ public class PotentialCreator
 
     private final AnnotatedWithParams creator;
 
-    private final JsonCreator.Mode creatorMode;
+    private JsonCreator.Mode creatorMode;
 
     private PropertyName[] implicitParamNames;
 
@@ -35,9 +35,29 @@ public PotentialCreator(AnnotatedWithParams cr,
             JsonCreator.Mode cm)
     {
         creator = cr;
+        if (cm == null) {
+            cm = JsonCreator.Mode.DEFAULT;
+        }
         creatorMode = cm;
     }
 
+    /**
+     * Method that can be called to change the {@code creatorMode} this
+     * Creator has: typically used to "mark" Creator as {@code JsonCreator.Mode.DELEGATING}
+     * or {@code JsonCreator.Mode.PROPERTIES} when further information is gathered).
+     *
+     * @param mode Mode to set {@code creatorMode} to
+     *
+     * @return This creator instance
+     */
+    public PotentialCreator overrideMode(JsonCreator.Mode mode) {
+        if (mode == null) {
+            mode = JsonCreator.Mode.DEFAULT;
+        }
+        creatorMode = mode;
+        return this;
+    }
+
     /*
     /**********************************************************************
     /* Mutators