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new 0736cdbfb fix(java): handle TypeVariable in row format type inference
(#2949)
0736cdbfb is described below
commit 0736cdbfb3c1a8d10f9c3859fb52ffe77e84beb9
Author: Shawn Yang <[email protected]>
AuthorDate: Sun Nov 30 19:09:58 2025 +0800
fix(java): handle TypeVariable in row format type inference (#2949)
## What does this PR do?
When inferring field types for row format encoding, TypeVariable types
(like K, V from Map<K, V>) were not handled, causing
UnsupportedOperationException with message like "Unsupported type K".
This can happen with Scala 3 LTS where generic type information may not
be fully resolved in the bytecode. The fix resolves TypeVariable to its
bound (e.g., K -> Object) before proceeding with type inference.
## Related issues
Fixes #2439
## Does this PR introduce any user-facing change?
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- [ ] Does this PR introduce any public API change?
- [ ] Does this PR introduce any binary protocol compatibility change?
## Benchmark
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---
.../org/apache/fory/format/type/TypeInference.java | 10 ++++
.../apache/fory/format/type/TypeInferenceTest.java | 53 ++++++++++++++++++++++
2 files changed, 63 insertions(+)
diff --git
a/java/fory-format/src/main/java/org/apache/fory/format/type/TypeInference.java
b/java/fory-format/src/main/java/org/apache/fory/format/type/TypeInference.java
index b34c8d0cf..4617f04fa 100644
---
a/java/fory-format/src/main/java/org/apache/fory/format/type/TypeInference.java
+++
b/java/fory-format/src/main/java/org/apache/fory/format/type/TypeInference.java
@@ -21,6 +21,8 @@ package org.apache.fory.format.type;
import static org.apache.fory.type.TypeUtils.getRawType;
+import java.lang.reflect.Type;
+import java.lang.reflect.TypeVariable;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
@@ -134,6 +136,14 @@ public class TypeInference {
* @return DataType of a typeToken
*/
private static Field inferField(String name, TypeRef<?> typeRef,
TypeResolutionContext ctx) {
+ // Handle TypeVariable (e.g., K, V from Map<K, V>) by resolving to its
bound.
+ // This can happen with Scala 3 LTS where generic type information may not
be fully resolved.
+ Type type = typeRef.getType();
+ if (type instanceof TypeVariable) {
+ TypeVariable<?> typeVariable = (TypeVariable<?>) type;
+ Type bound = typeVariable.getBounds()[0]; // First bound is a class,
others are interfaces
+ return inferField(name, TypeRef.of(bound), ctx);
+ }
Class<?> rawType = getRawType(typeRef);
Class<?> enclosingType = ctx.getEnclosingType().getRawType();
CustomCodec<?, ?> customEncoder =
diff --git
a/java/fory-format/src/test/java/org/apache/fory/format/type/TypeInferenceTest.java
b/java/fory-format/src/test/java/org/apache/fory/format/type/TypeInferenceTest.java
index 69468a2ec..4274b2464 100644
---
a/java/fory-format/src/test/java/org/apache/fory/format/type/TypeInferenceTest.java
+++
b/java/fory-format/src/test/java/org/apache/fory/format/type/TypeInferenceTest.java
@@ -21,10 +21,14 @@ package org.apache.fory.format.type;
import static org.testng.Assert.assertEquals;
import static org.testng.Assert.assertNotNull;
+import static org.testng.Assert.assertTrue;
import com.google.common.base.CaseFormat;
+import java.lang.reflect.TypeVariable;
import java.util.List;
+import java.util.Map;
import java.util.stream.Collectors;
+import org.apache.fory.reflect.TypeRef;
import org.apache.fory.test.bean.BeanA;
import org.apache.fory.type.Descriptor;
import org.testng.annotations.Test;
@@ -43,4 +47,53 @@ public class TypeInferenceTest {
assertEquals(fieldNames, expectedFieldNames);
assertNotNull(schema.getFieldByName("double_list"));
}
+
+ /**
+ * Test that TypeVariable types (like K, V from Map<K, V>) are handled
correctly by resolving to
+ * their bounds. This can happen with Scala 3 LTS where generic type
information may not be fully
+ * resolved. See https://github.com/apache/fory/issues/2439
+ */
+ @Test
+ public void testTypeVariableInference() {
+ // Get the TypeVariable K from Map<K, V>
+ TypeVariable<?>[] typeParams = Map.class.getTypeParameters();
+ assertEquals(typeParams.length, 2);
+ TypeVariable<?> keyTypeVar = typeParams[0]; // K
+ TypeVariable<?> valueTypeVar = typeParams[1]; // V
+
+ // Verify these are indeed TypeVariables
+ assertTrue(keyTypeVar instanceof TypeVariable);
+ assertTrue(valueTypeVar instanceof TypeVariable);
+
+ // TypeVariable K has bound Object which is not a supported row format
type,
+ // but the TypeVariable resolution itself should work.
+ // The fix ensures TypeVariable is resolved to its bound before failing.
+ TypeRef<?> keyTypeRef = TypeRef.of(keyTypeVar);
+ try {
+ TypeInference.inferDataType(keyTypeRef);
+ } catch (UnsupportedOperationException e) {
+ // Expected: Object is not a supported type, but the error should
mention Object,
+ // not the TypeVariable name "K"
+ assertTrue(
+ e.getMessage().contains("java.lang.Object"),
+ "TypeVariable should be resolved to Object, not remain as K");
+ }
+ }
+
+ /** Test inferring schema for a class with Map field containing Long keys
and values. */
+ @Test
+ public void testMapFieldTypeInference() {
+ Schema schema = TypeInference.inferSchema(ClassWithMapField.class);
+ assertNotNull(schema);
+ Field mapField = schema.getFieldByName("long_map");
+ assertNotNull(mapField);
+ assertTrue(mapField.type() instanceof DataTypes.MapType);
+ DataTypes.MapType mapType = (DataTypes.MapType) mapField.type();
+ assertEquals(mapType.keyType(), DataTypes.int64());
+ assertEquals(mapType.itemType(), DataTypes.int64());
+ }
+
+ private static class ClassWithMapField {
+ public Map<Long, Long> longMap;
+ }
}
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