cel-expr · copybara-service · Jun 9, 2026 · Jun 9, 2026
diff --git a/extensions/src/main/java/dev/cel/extensions/BUILD.bazel b/extensions/src/main/java/dev/cel/extensions/BUILD.bazel
@@ -329,6 +329,7 @@ java_library(
     deps = [
         "//checker:checker_builder",
         "//common/exceptions:attribute_not_found",
+        "//common/exceptions:invalid_argument",
         "//common/internal:reflection_util",
         "//common/types",
         "//common/types:type_providers",

diff --git a/extensions/src/main/java/dev/cel/extensions/CelNativeTypesExtensions.java b/extensions/src/main/java/dev/cel/extensions/CelNativeTypesExtensions.java
@@ -28,6 +28,7 @@
 import com.google.errorprone.annotations.Immutable;
 import dev.cel.checker.CelCheckerBuilder;
 import dev.cel.common.exceptions.CelAttributeNotFoundException;
+import dev.cel.common.exceptions.CelInvalidArgumentException;
 import dev.cel.common.internal.ReflectionUtil;
 import dev.cel.common.types.CelType;
 import dev.cel.common.types.CelTypeProvider;
@@ -47,6 +48,7 @@
 import dev.cel.runtime.CelRuntimeLibrary;
 import java.lang.invoke.MethodHandle;
 import java.lang.invoke.MethodHandles;
+import java.lang.reflect.Array;
 import java.lang.reflect.Constructor;
 import java.lang.reflect.Field;
 import java.lang.reflect.Method;
@@ -289,6 +291,15 @@ private static CelType mapJavaTypeToCelType(
         return celType;
       }
 
+      if (type.isArray()) {
+        TypeToken<?> token = TypeToken.of(genericType);
+        TypeToken<?> componentToken =
+            Preconditions.checkNotNull(
+                token.getComponentType(), "Array component type cannot be null");
+        return ListType.create(
+            mapJavaTypeToCelType(componentToken.getRawType(), componentToken.getType(), classMap));
+      }
+
       if (type.isInterface()
           && !List.class.isAssignableFrom(type)
           && !Map.class.isAssignableFrom(type)) {
@@ -416,6 +427,14 @@ private void discover(Type type) {
         TypeToken<?> token = TypeToken.of(type);
         Class<?> rawType = token.getRawType();
 
+        if (rawType.isArray()) {
+          TypeToken<?> componentToken =
+              Preconditions.checkNotNull(
+                  token.getComponentType(), "Array component type cannot be null");
+          discover(componentToken.getType());
+          return;
+        }
+
         if (List.class.isAssignableFrom(rawType)) {
           discover(ReflectionUtil.resolveGenericParameter(token, List.class, 0));
           return;
@@ -775,6 +794,9 @@ private static Object getDefaultValue(Class<?> targetType) {
       if (Map.class.isAssignableFrom(targetType)) {
         return ImmutableMap.of();
       }
+      if (targetType.isArray()) {
+        return Array.newInstance(targetType.getComponentType(), 0);
+      }
 
       try {
         Constructor<?> constructor = targetType.getDeclaredConstructor();
@@ -822,6 +844,10 @@ public Object toRuntimeValue(Object value) {
         return new PojoStructValue(value, accessors, registry.classToTypeMap.get(clazz));
       }
 
+      if (clazz.isArray() && clazz != byte[].class) {
+        return convertArrayToList(value);
+      }
+
       return super.toRuntimeValue(value);
     }
 
@@ -844,8 +870,14 @@ Object toNative(Object value, Class<?> targetType, Type genericType) {
         return ((CelByteString) value).toByteArray();
       }
 
-      if (List.class.isAssignableFrom(targetType) && value instanceof List) {
-        return convertListToNative((List<?>) value, targetType, genericType);
+      if (value instanceof List) {
+        List<?> listValue = (List<?>) value;
+        if (List.class.isAssignableFrom(targetType)) {
+          return convertListToNative(listValue, targetType, genericType);
+        }
+        if (targetType.isArray()) {
+          return convertListToArray(listValue, targetType, genericType);
+        }
       }
 
       if (Map.class.isAssignableFrom(targetType) && value instanceof Map) {
@@ -857,7 +889,7 @@ Object toNative(Object value, Class<?> targetType, Type genericType) {
 
     // Safe reflection collection cast.
     @SuppressWarnings("unchecked")
-    private Object convertListToNative(List<?> list, Class<?> targetType, Type genericType) {
+    private List<?> convertListToNative(List<?> list, Class<?> targetType, Type genericType) {
       TypeToken<?> token = TypeToken.of(genericType);
       Type elementType = ReflectionUtil.resolveGenericParameter(token, List.class, 0);
       Class<?> componentType = ReflectionUtil.getRawType(elementType);
@@ -909,7 +941,7 @@ private Object convertListToNative(List<?> list, Class<?> targetType, Type gener
 
     // Safe reflection collection cast.
     @SuppressWarnings("unchecked")
-    private Object convertMapToNative(Map<?, ?> map, Class<?> targetType, Type genericType) {
+    private Map<?, ?> convertMapToNative(Map<?, ?> map, Class<?> targetType, Type genericType) {
       TypeToken<?> token = TypeToken.of(genericType);
       Type keyType = ReflectionUtil.resolveGenericParameter(token, Map.class, 0);
       Type valueType = ReflectionUtil.resolveGenericParameter(token, Map.class, 1);
@@ -970,6 +1002,36 @@ private Object convertMapToNative(Map<?, ?> map, Class<?> targetType, Type gener
       return builder.buildOrThrow();
     }
 
+    private Object convertListToArray(List<?> list, Class<?> targetType, Type genericType) {
+      Class<?> componentType = targetType.getComponentType();
+      Object array = Array.newInstance(componentType, list.size());
+      TypeToken<?> token = TypeToken.of(genericType);
+      TypeToken<?> componentToken =
+          Preconditions.checkNotNull(
+              token.getComponentType(), "Array component type cannot be null");
+      Type componentGenericType = componentToken.getType();
+
+      for (int i = 0; i < list.size(); i++) {
+        Object element = list.get(i);
+        Object converted = toNative(element, componentType, componentGenericType);
+        Array.set(array, i, converted);
+      }
+      return array;
+    }
+
+    private ImmutableList<Object> convertArrayToList(Object array) {
+      int length = Array.getLength(array);
+      ImmutableList.Builder<Object> builder = ImmutableList.builderWithExpectedSize(length);
+      for (int i = 0; i < length; i++) {
+        Object element = Array.get(array, i);
+        if (element == null) {
+          throw new CelInvalidArgumentException(String.format("Element at index %d is null.", i));
+        }
+        builder.add(toRuntimeValue(element));
+      }
+      return builder.build();
+    }
+
     private Object downcastPrimitives(Object value, Class<?> targetType) {
       Class<?> wrappedTargetType = Primitives.wrap(targetType);
       if (wrappedTargetType == Integer.class && value instanceof Long) {

diff --git a/extensions/src/main/java/dev/cel/extensions/README.md b/extensions/src/main/java/dev/cel/extensions/README.md
@@ -1114,14 +1114,14 @@ The type-mapping between Java and CEL is as follows:
 | `String` | `string` |
 | `java.time.Duration` | `duration` |
 | `java.time.Instant` | `timestamp` |
-| `java.util.List` | `list` |
+| `java.util.List`, `T[]` (except `byte[]`) | `list` |
 | `java.util.Map` | `map` |
 | `java.util.Optional` | `optional_type` |
 
 ### Notes
 
 *   This is only supported for the planner runtime (e.g., `CelRuntimeFactory.plannerRuntimeBuilder()`).
-*   Native Java arrays (except `byte[]`) are not supported. Use `java.util.List` instead.
+*   Native Java arrays are supported. `byte[]` maps to `bytes`, while other arrays map to `list`.
 *   Java `enum` properties are not currently supported and will be safely ignored during scanning.
 *   If there is a name collision with a Protobuf type, the protobuf type will take precedence.
 *   Instantiating new struct values (e.g., `Account{id: 1234}`) requires the class to have a no-argument constructor (public, protected, package-private, or private).

diff --git a/extensions/src/test/java/dev/cel/extensions/BUILD.bazel b/extensions/src/test/java/dev/cel/extensions/BUILD.bazel
@@ -20,6 +20,7 @@ java_library(
         "//common/exceptions:attribute_not_found",
         "//common/exceptions:divide_by_zero",
         "//common/exceptions:index_out_of_bounds",
+        "//common/exceptions:invalid_argument",
         "//common/types",
         "//common/types:type_providers",
         "//common/values",

diff --git a/extensions/src/test/java/dev/cel/extensions/CelNativeTypesExtensionsTest.java b/extensions/src/test/java/dev/cel/extensions/CelNativeTypesExtensionsTest.java
@@ -30,6 +30,7 @@
 import dev.cel.common.CelContainer;
 import dev.cel.common.CelValidationException;
 import dev.cel.common.exceptions.CelAttributeNotFoundException;
+import dev.cel.common.exceptions.CelInvalidArgumentException;
 import dev.cel.common.types.CelType;
 import dev.cel.common.types.ListType;
 import dev.cel.common.types.MapType;
@@ -90,7 +91,8 @@ public final class CelNativeTypesExtensionsTest {
           TestGetterFieldTypeMismatchPojo.class,
           TestAbstractPojo.class,
           TestURLPojo.class,
-          PojoWithEnum.class);
+          PojoWithEnum.class,
+          TestArrayPojo.class);
 
   private static final Cel CEL =
       CelFactory.plannerCelBuilder()
@@ -323,10 +325,10 @@ public void nativeTypes_anonymousClass_throwsException() {
 
   @Test
   public void nativeTypes_createStruct_privateConstructor() throws Exception {
-    Object result = eval("TestPrivateConstructorPojo{value:" + " 'hello'}");
+    TestPrivateConstructorPojo result =
+        (TestPrivateConstructorPojo) eval("TestPrivateConstructorPojo{value:" + " 'hello'}");
 
-    assertThat(result).isInstanceOf(TestPrivateConstructorPojo.class);
-    assertThat(((TestPrivateConstructorPojo) result).value).isEqualTo("hello");
+    assertThat(result.value).isEqualTo("hello");
   }
 
   @Test
@@ -375,10 +377,9 @@ public void nativeTypes_missingNoArgConstructor_throws() throws Exception {
 
   @Test
   public void nativeTypes_createWithDeepConversion() throws Exception {
-    Object result = eval("TestDeepConversionPojo{ints: [1, 2], floats: {'a': 1.0, 'b': 2.0}}");
-
-    assertThat(result).isInstanceOf(TestDeepConversionPojo.class);
-    TestDeepConversionPojo pojo = (TestDeepConversionPojo) result;
+    TestDeepConversionPojo pojo =
+        (TestDeepConversionPojo)
+            eval("TestDeepConversionPojo{ints: [1, 2], floats: {'a': 1.0, 'b': 2.0}}");
     assertThat(pojo.ints.get(0)).isEqualTo(1);
     assertThat(pojo.floats).containsEntry("a", 1.0f);
   }
@@ -398,11 +399,92 @@ public void nativeTypes_unsupportedTypeSet_throwsOnRegistration() throws Excepti
   }
 
   @Test
-  public void nativeTypes_arrayType_throwsOnRegistration() throws Exception {
-    IllegalArgumentException e =
+  public void nativeTypes_arrayType_construction() throws Exception {
+    String expr =
+        "TestArrayPojo{"
+            + "  strings: ['a', 'b'],"
+            + "  ints: [1, 2],"
+            + "  nesteds: [TestNestedType{value: 'nested'}],"
+            + "  matrix: [[1, 2], [3, 4]],"
+            + "  nestedMatrix: [[TestNestedType{value: 'm1'}], [TestNestedType{value: 'm2'}]],"
+            + "  byteArrays: [b'foo', b'bar']"
+            + "}";
+
+    TestArrayPojo pojo = (TestArrayPojo) eval(expr);
+
+    assertThat(pojo.strings).isEqualTo(new String[] {"a", "b"});
+    assertThat(pojo.ints).isEqualTo(new int[] {1, 2});
+    assertThat(pojo.nesteds).hasLength(1);
+    assertThat(pojo.nesteds[0].value).isEqualTo("nested");
+    assertThat(pojo.matrix).hasLength(2);
+    assertThat(pojo.matrix[0]).isEqualTo(new int[] {1, 2});
+    assertThat(pojo.matrix[1]).isEqualTo(new int[] {3, 4});
+    assertThat(pojo.nestedMatrix).hasLength(2);
+    assertThat(pojo.nestedMatrix[0][0].value).isEqualTo("m1");
+    assertThat(pojo.nestedMatrix[1][0].value).isEqualTo("m2");
+    assertThat(pojo.byteArrays).hasLength(2);
+    assertThat(pojo.byteArrays[0]).isEqualTo("foo".getBytes(UTF_8));
+    assertThat(pojo.byteArrays[1]).isEqualTo("bar".getBytes(UTF_8));
+  }
+
+  @Test
+  public void nativeTypes_arrayType_selection() throws Exception {
+    CelNativeTypesExtensions extensions = CelExtensions.nativeTypes(TestArrayPojo.class);
+    Cel cel =
+        CelFactory.plannerCelBuilder()
+            .setContainer(CelContainer.ofName("dev.cel.extensions.CelNativeTypesExtensionsTest"))
+            .addCompilerLibraries(extensions)
+            .addRuntimeLibraries(extensions)
+            .addVar("pojo", StructTypeReference.create(TestArrayPojo.class.getCanonicalName()))
+            .build();
+    String expr =
+        "pojo.strings[1] == 'b'"
+            + "  && pojo.ints[0] == 1"
+            + "  && pojo.nesteds[0].value == 'nested'"
+            + "  && pojo.matrix[1][0] == 3"
+            + "  && pojo.nestedMatrix[1][0].value == 'm2'"
+            + "  && pojo.byteArrays[1] == b'bar'";
+    CelAbstractSyntaxTree ast = cel.compile(expr).getAst();
+    CelRuntime.Program program = cel.createProgram(ast);
+
+    TestArrayPojo input = new TestArrayPojo();
+    input.strings = new String[] {"a", "b"};
+    input.ints = new int[] {1, 2};
+    TestNestedType nested = new TestNestedType();
+    nested.value = "nested";
+    input.nesteds = new TestNestedType[] {nested};
+    input.matrix = new int[][] {{1, 2}, {3, 4}};
+    TestNestedType m1 = new TestNestedType();
+    m1.value = "m1";
+    TestNestedType m2 = new TestNestedType();
+    m2.value = "m2";
+    input.nestedMatrix = new TestNestedType[][] {{m1}, {m2}};
+    input.byteArrays = new byte[][] {"foo".getBytes(UTF_8), "bar".getBytes(UTF_8)};
+
+    assertThat(program.eval(ImmutableMap.of("pojo", input))).isEqualTo(true);
+  }
+
+  @Test
+  public void nativeTypes_arrayWithNullElement_throws() throws Exception {
+    CelNativeTypesExtensions extensions = CelExtensions.nativeTypes(TestArrayPojo.class);
+    Cel cel =
+        CelFactory.plannerCelBuilder()
+            .setContainer(CelContainer.ofName("dev.cel.extensions.CelNativeTypesExtensionsTest"))
+            .addCompilerLibraries(extensions)
+            .addRuntimeLibraries(extensions)
+            .addVar("pojo", StructTypeReference.create(TestArrayPojo.class.getCanonicalName()))
+            .build();
+    CelAbstractSyntaxTree ast = cel.compile("pojo.strings").getAst();
+    CelRuntime.Program program = cel.createProgram(ast);
+
+    TestArrayPojo input = new TestArrayPojo();
+    input.strings = new String[] {"a", null, "c"};
+
+    CelEvaluationException e =
         assertThrows(
-            IllegalArgumentException.class, () -> CelExtensions.nativeTypes(TestArrayPojo.class));
-    assertThat(e).hasMessageThat().contains("Unsupported type for property 'values'");
+            CelEvaluationException.class, () -> program.eval(ImmutableMap.of("pojo", input)));
+    assertThat(e).hasCauseThat().isInstanceOf(CelInvalidArgumentException.class);
+    assertThat(e).hasCauseThat().hasMessageThat().contains("Element at index 1 is null.");
   }
 
   @Test
@@ -662,10 +744,7 @@ public void nativeTypes_createWithUint_fromUnsignedLong() throws Exception {
             .getAst();
     CelRuntime.Program program = celRuntime.createProgram(ast);
 
-    Object result = program.eval();
-
-    assertThat(result).isInstanceOf(TestAllTypesPublicFieldsPojo.class);
-    TestAllTypesPublicFieldsPojo pojo = (TestAllTypesPublicFieldsPojo) result;
+    TestAllTypesPublicFieldsPojo pojo = (TestAllTypesPublicFieldsPojo) program.eval();
     assertThat(pojo.uintVal).isEqualTo(UnsignedLong.fromLongBits(42L));
   }
 
@@ -782,6 +861,8 @@ public void nativeTypes_nullSafeTraversal() throws Exception {
     assertThat(cel.createProgram(cel.compile("pojo.int64Val").getAst()).eval(vars)).isEqualTo(0L);
     assertThat(cel.createProgram(cel.compile("pojo.nestedVal.value").getAst()).eval(vars))
         .isEqualTo("");
+    assertThat(cel.createProgram(cel.compile("size(pojo.arrayVal) == 0").getAst()).eval(vars))
+        .isEqualTo(true);
     CelAbstractSyntaxTree abstractPojoAst = cel.compile("pojo.abstractPojo.value").getAst();
     CelRuntime.Program abstractPojoProgram = cel.createProgram(abstractPojoAst);
     CelEvaluationException e =
@@ -942,6 +1023,7 @@ public String get() {
     public double doubleVal;
     public float floatVal;
     public byte[] bytesVal;
+    public String[] arrayVal;
     public Duration durationVal;
     public Instant timestampVal;
     public TestNestedType nestedVal;
@@ -1259,7 +1341,12 @@ public static class TestWildcardPojo {
   }
 
   public static class TestArrayPojo {
-    public String[] values;
+    public String[] strings;
+    public int[] ints;
+    public TestNestedType[] nesteds;
+    public int[][] matrix;
+    public TestNestedType[][] nestedMatrix;
+    public byte[][] byteArrays;
   }
 
   public static class TestOptionalUrlPojo {