Introduce ProtoUnsetFieldOptions to support unset handling like C++

PiperOrigin-RevId: 655712342

common/src/main/java/dev/cel/common/CelOptions.java

@@ -30,6 +30,18 @@
 @Immutable
 public abstract class CelOptions {
 
+  /**
+   * ProtoUnsetFieldOptions describes how to handle Activation.fromProto() calls where proto message
+   * fields may be unset and should either be handled perhaps as absent or as the default proto
+   * value.
+   */
+  public enum ProtoUnsetFieldOptions {
+    // Do not bind a field if it is unset. Repeated fields are bound as empty list.
+    SKIP,
+    // Bind the (proto api) default value for a field.
+    BIND_DEFAULT;
+  }
+
   public static final CelOptions DEFAULT = current().build();
 
   public static final CelOptions LEGACY = newBuilder().disableCelStandardEquality(true).build();
@@ -95,6 +107,8 @@ public abstract class CelOptions {
 
   public abstract boolean unwrapWellKnownTypesOnFunctionDispatch();
 
+  public abstract ProtoUnsetFieldOptions fromProtoUnsetFieldOption();
+
   public abstract Builder toBuilder();
 
   public ImmutableSet<ExprFeatures> toExprFeatures() {
@@ -185,7 +199,8 @@ public static Builder newBuilder() {
         .enableUnknownTracking(false)
         .enableCelValue(false)
         .comprehensionMaxIterations(-1)
-        .unwrapWellKnownTypesOnFunctionDispatch(true);
+        .unwrapWellKnownTypesOnFunctionDispatch(true)
+        .fromProtoUnsetFieldOption(ProtoUnsetFieldOptions.BIND_DEFAULT);
   }
 
   /**
@@ -479,6 +494,15 @@ public abstract static class Builder {
     @Deprecated
     public abstract Builder unwrapWellKnownTypesOnFunctionDispatch(boolean value);
 
+    /**
+     * Configure how unset proto fields are handled when evaluating over a protobuf message where
+     * fields are intended to be treated as top-level variables. Defaults to binding all fields to
+     * their default value if unset.
+     *
+     * @see ProtoUnsetFieldOptions
+     */
+    public abstract Builder fromProtoUnsetFieldOption(ProtoUnsetFieldOptions value);
+
     public abstract CelOptions build();
   }
 }

runtime/src/main/java/dev/cel/runtime/Activation.java

@@ -172,7 +172,15 @@ public static Activation fromProto(Message message, CelOptions celOptions) {
         new ProtoAdapter(
             DynamicProto.create(DefaultMessageFactory.INSTANCE), celOptions.enableUnsignedLongs());
 
+    boolean skipUnsetFields =
+        celOptions.fromProtoUnsetFieldOption().equals(CelOptions.ProtoUnsetFieldOptions.SKIP);
+
     for (FieldDescriptor field : message.getDescriptorForType().getFields()) {
+      // If skipping unset fields and the field is not repeated, then continue.
+      if (skipUnsetFields && !field.isRepeated() && !msgFieldValues.containsKey(field)) {
+        continue;
+      }
+
       // Get the value of the field set on the message, if present, otherwise use reflection to
       // get the default value for the field using the FieldDescriptor.
       Object fieldValue = msgFieldValues.getOrDefault(field, message.getField(field));

runtime/src/test/java/dev/cel/runtime/ActivationTest.java

@@ -35,6 +35,13 @@ public final class ActivationTest {
   private static final CelOptions TEST_OPTIONS =
       CelOptions.current().enableTimestampEpoch(true).enableUnsignedLongs(true).build();
 
+  private static final CelOptions TEST_OPTIONS_SKIP_UNSET_FIELDS =
+      CelOptions.current()
+          .enableTimestampEpoch(true)
+          .enableUnsignedLongs(true)
+          .fromProtoUnsetFieldOption(CelOptions.ProtoUnsetFieldOptions.SKIP)
+          .build();
+
   @Test
   public void copyOf_success_withNullEntries() {
     Map<String, Object> map = new HashMap<>();
@@ -64,6 +71,13 @@ public void fromProto_unsetScalarField() {
     assertThat(activation.resolve("bb")).isEqualTo(0);
   }
 
+  @Test
+  public void fromProto_unsetScalarField_skipUnsetFields() {
+    Activation activation =
+        Activation.fromProto(NestedMessage.getDefaultInstance(), TEST_OPTIONS_SKIP_UNSET_FIELDS);
+    assertThat(activation.resolve("bb")).isNull();
+  }
+
   @Test
   public void fromProto_unsetAnyField() {
     // An unset Any field is the only field which cannot be accurately published into an Activation,
@@ -102,13 +116,32 @@ public void fromProto_unsetRepeatedField() {
     assertThat((List) activation.resolve("repeated_nested_message")).isEmpty();
   }
 
+  @Test
+  public void fromProto_unsetRepeatedField_skipUnsetFields() {
+    Activation activation =
+        Activation.fromProto(TestAllTypes.getDefaultInstance(), TEST_OPTIONS_SKIP_UNSET_FIELDS);
+    assertThat(activation.resolve("repeated_int64")).isInstanceOf(List.class);
+    assertThat((List) activation.resolve("repeated_int64")).isEmpty();
+
+    assertThat(activation.resolve("repeated_nested_message")).isInstanceOf(List.class);
+    assertThat((List) activation.resolve("repeated_nested_message")).isEmpty();
+  }
+
   @Test
   public void fromProto_unsetMapField() {
     Activation activation = Activation.fromProto(TestAllTypes.getDefaultInstance(), TEST_OPTIONS);
     assertThat(activation.resolve("map_int32_int64")).isInstanceOf(Map.class);
     assertThat((Map) activation.resolve("map_int32_int64")).isEmpty();
   }
 
+  @Test
+  public void fromProto_unsetMapField_skipUnsetFields() {
+    Activation activation =
+        Activation.fromProto(TestAllTypes.getDefaultInstance(), TEST_OPTIONS_SKIP_UNSET_FIELDS);
+    assertThat(activation.resolve("map_int32_int64")).isInstanceOf(Map.class);
+    assertThat((Map) activation.resolve("map_int32_int64")).isEmpty();
+  }
+
   @Test
   public void fromProto_unsignedLongField_unsignedResult() {
     Activation activation =