Fix #4443: detect Iterable as IterationType (#4487)

Author: cowtowncoder

release-notes/VERSION-2.x

@@ -6,6 +6,8 @@ Project: jackson-databind
 
 2.18.0 (not yet released)
 
+#4443: Add `Iterable<T>` as recognized `IterationType` instance (along with
+  `Iterable`, `Stream`)
 #4453: Allow JSON Integer to deserialize into a single-arg constructor of
   parameter type `double`
  (contributed by David M)

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

@@ -1637,7 +1637,9 @@ protected JavaType _fromWellKnownClass(ClassStack context, Class<?> rawType, Typ
         //    detected, related to difficulties in propagating type upwards (Iterable, for
         //    example, is a weak, tag-on type). They may be detectable in future.
         // 23-May-2023, tatu: As of 2.16 we do, however, recognized certain `IterationType`s.
-        if (rawType == Iterator.class || rawType == Stream.class) {
+        if (rawType == Iterator.class || rawType == Stream.class
+                // 18-Apr-2024, tatu: [databind#4443] allow exact `Iterable`
+                || rawType == Iterable.class) {
             return _iterationType(rawType, bindings, superClass, superInterfaces);
         }
         if (BaseStream.class.isAssignableFrom(rawType)) {

src/test/java/com/fasterxml/jackson/databind/type/JavaTypeTest.java

@@ -324,6 +324,8 @@ public void testIterationTypesDirect() throws Exception
                 Iterator.class, Object.class);
         _verifyIteratorType(tf.constructType(Stream.class),
                 Stream.class, Object.class);
+        _verifyIteratorType(tf.constructType(Iterable.class),
+                Iterable.class, Object.class);
 
         // Then generic but direct
         JavaType t = _verifyIteratorType(tf.constructType(new TypeReference<Iterator<String>>() { }),

src/test/java/com/fasterxml/jackson/databind/type/TypeFactoryTest.java

@@ -165,6 +165,19 @@ public void testIterator()
         assertNull(t.containedType(1));
     }
 
+    // [databind#4443]
+    @Test
+    public void testIterable()
+    {
+        TypeFactory tf = TypeFactory.defaultInstance();
+        JavaType t = tf.constructType(new TypeReference<Iterable<String>>() { });
+        assertEquals(IterationType.class, t.getClass());
+        assertTrue(t.isIterationType());
+        assertSame(Iterable.class, t.getRawClass());
+        assertEquals(1, t.containedTypeCount());
+        assertEquals(tf.constructType(String.class), t.containedType(0));
+        assertNull(t.containedType(1));
+    }
     /**
      * Test for verifying that parametric types can be constructed
      * programmatically