Introduce OptimizedSelectable interface and general traversal logic on

common/src/main/java/dev/cel/common/values/BUILD.bazel

@@ -434,3 +434,85 @@ cel_android_library(
         "@maven//:com_google_errorprone_error_prone_annotations",
     ],
 )
+
+java_library(
+    name = "select_field",
+    srcs = ["SelectField.java"],
+    tags = [
+    ],
+    deps = [
+        "//:auto_value",
+        "//common/annotations",
+        "@maven//:com_google_errorprone_error_prone_annotations",
+        "@maven//:com_google_guava_guava",
+        "@maven//:org_jspecify_jspecify",
+    ],
+)
+
+cel_android_library(
+    name = "select_field_android",
+    srcs = ["SelectField.java"],
+    tags = [
+    ],
+    deps = [
+        "//:auto_value",
+        "//common/annotations",
+        "@maven//:com_google_errorprone_error_prone_annotations",
+        "@maven//:org_jspecify_jspecify",
+        "@maven_android//:com_google_guava_guava",
+    ],
+)
+
+java_library(
+    name = "optimized_selectable",
+    srcs = ["OptimizedSelectable.java"],
+    tags = [
+    ],
+    deps = [
+        ":select_field",
+        "//common/annotations",
+        "@maven//:com_google_errorprone_error_prone_annotations",
+    ],
+)
+
+cel_android_library(
+    name = "optimized_selectable_android",
+    srcs = ["OptimizedSelectable.java"],
+    tags = [
+    ],
+    deps = [
+        ":select_field_android",
+        "//common/annotations",
+        "@maven//:com_google_errorprone_error_prone_annotations",
+    ],
+)
+
+java_library(
+    name = "optimized_select_traversal",
+    srcs = ["OptimizedSelectTraversal.java"],
+    tags = [
+    ],
+    deps = [
+        ":optimized_selectable",
+        ":select_field",
+        ":values",
+        "//common/annotations",
+        "//common/exceptions:attribute_not_found",
+        "@maven//:com_google_guava_guava",
+    ],
+)
+
+cel_android_library(
+    name = "optimized_select_traversal_android",
+    srcs = ["OptimizedSelectTraversal.java"],
+    tags = [
+    ],
+    deps = [
+        ":optimized_selectable_android",
+        ":select_field_android",
+        ":values_android",
+        "//common/annotations",
+        "//common/exceptions:attribute_not_found",
+        "@maven_android//:com_google_guava_guava",
+    ],
+)

common/src/main/java/dev/cel/common/values/OptimizedSelectTraversal.java

@@ -0,0 +1,116 @@
+// Copyright 2026 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package dev.cel.common.values;
+
+import com.google.common.collect.ImmutableList;
+import dev.cel.common.annotations.Internal;
+import dev.cel.common.exceptions.CelAttributeNotFoundException;
+import java.util.Optional;
+
+/**
+ * Walks a sequence of {@link SelectField} selections, dispatching each field over {@link
+ * OptimizedSelectable} or {@link SelectableValue}.
+ *
+ * <p>CEL Library Internals. Do Not Use.
+ */
+@Internal
+public final class OptimizedSelectTraversal {
+
+  /**
+   * Qualifies {@code target} through every field in {@code fields} and returns the terminal value.
+   */
+  public static Object qualify(Object target, ImmutableList<SelectField> fields) {
+    Object current = target;
+    for (int i = 0; i < fields.size(); i++) {
+      current = qualifyField(current, fields.get(i));
+    }
+    return current;
+  }
+
+  /**
+   * Presence tests the terminal field of {@code fields}, navigating through all preceding fields.
+   *
+   * <p>Absence of any intermediate field short-circuits to {@code false}.
+   */
+  public static boolean hasField(Object target, ImmutableList<SelectField> fields) {
+    if (fields.isEmpty()) {
+      return false;
+    }
+    Object current = target;
+    int terminalIndex = fields.size() - 1;
+    for (int i = 0; i < terminalIndex; i++) {
+      Optional<Object> next = navigateField(current, fields.get(i));
+      if (!next.isPresent()) {
+        return false;
+      }
+      current = next.get();
+    }
+    return hasTerminalField(current, fields.get(terminalIndex));
+  }
+
+  // SelectableValue is only ever instantiated with String keys in the select path.
+  @SuppressWarnings("unchecked")
+  private static Object qualifyField(Object target, SelectField field) {
+    if (target instanceof ErrorValue) {
+      return target;
+    }
+    if (target instanceof OptimizedSelectable) {
+      return ((OptimizedSelectable) target).selectByFieldNumber(field);
+    }
+    if (target instanceof SelectableValue) {
+      SelectableValue<String> selectable = (SelectableValue<String>) target;
+      if (field.defaultValue() != null) {
+        return selectable
+            .find(field.fieldName())
+            .map(Object.class::cast)
+            .orElse(field.defaultValue());
+      }
+      return selectable.select(field.fieldName());
+    }
+    throw CelAttributeNotFoundException.forFieldResolution(field.fieldName());
+  }
+
+  // SelectableValue is only ever instantiated with String keys in the select path.
+  @SuppressWarnings("unchecked")
+  private static Optional<Object> navigateField(Object target, SelectField field) {
+    if (target instanceof ErrorValue) {
+      return Optional.of(target);
+    }
+    if (target instanceof OptimizedSelectable) {
+      return ((OptimizedSelectable) target).findByFieldNumber(field);
+    }
+    if (target instanceof SelectableValue) {
+      return ((SelectableValue<String>) target).find(field.fieldName()).map(Object.class::cast);
+    }
+    throw CelAttributeNotFoundException.forFieldResolution(field.fieldName());
+  }
+
+  // SelectableValue is only ever instantiated with String keys in the select path.
+  @SuppressWarnings("unchecked")
+  private static boolean hasTerminalField(Object target, SelectField field) {
+    if (target instanceof ErrorValue) {
+      return false;
+    }
+    if (target instanceof OptimizedSelectable) {
+      return ((OptimizedSelectable) target).hasFieldByNumber(field);
+    }
+    if (target instanceof SelectableValue) {
+      return ((SelectableValue<String>) target).find(field.fieldName()).isPresent();
+    }
+    throw CelAttributeNotFoundException.forFieldResolution(field.fieldName());
+  }
+
+  private OptimizedSelectTraversal() {}
+}

common/src/main/java/dev/cel/common/values/OptimizedSelectable.java

@@ -0,0 +1,45 @@
+// Copyright 2026 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package dev.cel.common.values;
+
+import com.google.errorprone.annotations.Immutable;
+import dev.cel.common.annotations.Internal;
+import java.util.Optional;
+
+/**
+ * Resolves an optimized field selection within a selection chain rewritten by the select optimizer.
+ *
+ * <p>Implementations resolve individual field selections against themselves by protobuf field
+ * number. Walking the chain across multiple fields and heterogeneous values belongs to {@link
+ * OptimizedSelectTraversal}.
+ *
+ * <p>CEL Library Internals. Do Not Use.
+ */
+@Internal
+@Immutable
+public interface OptimizedSelectable {
+
+  /** Selects {@code field}, falling back to its default value or an empty submessage if absent. */
+  Object selectByFieldNumber(SelectField field);
+
+  /** Returns whether {@code field} is present. */
+  boolean hasFieldByNumber(SelectField field);
+
+  /**
+   * Returns the value of the field at {@code field} (a scalar or submessage) for an intermediate
+   * step of a presence test, or empty if absent.
+   */
+  Optional<Object> findByFieldNumber(SelectField field);
+}

common/src/main/java/dev/cel/common/values/SelectField.java

@@ -0,0 +1,124 @@
+// Copyright 2026 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package dev.cel.common.values;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static com.google.common.base.Preconditions.checkNotNull;
+
+import com.google.auto.value.AutoValue;
+import com.google.errorprone.annotations.Immutable;
+import dev.cel.common.annotations.Internal;
+import org.jspecify.annotations.Nullable;
+
+/**
+ * Represents a single field selection in an optimized selection chain.
+ *
+ * <p>CEL Library Internals. Do Not Use.
+ */
+@Internal
+@AutoValue
+@AutoValue.CopyAnnotations
+@Immutable
+@SuppressWarnings("Immutable") // Default value is an immutable CEL literal or null
+public abstract class SelectField {
+
+  private static final int MAX_FIELD_NUMBER = 536870911;
+
+  /** CEL-specific type code used to encode CEL maps on the wire. */
+  public static final int CEL_MAP_TYPE_CODE = -1;
+
+  /** Sentinel for a presence-test qualifier, whose 2-tuple carries no type code. */
+  public static final int NO_TYPE_CODE = 0;
+
+  /** Protobuf field type code for {@code TYPE_MESSAGE} ({@code FieldDescriptorProto.Type}). */
+  public static final int MESSAGE_TYPE_CODE = 11;
+
+  // Mirrors FieldDescriptorProto.Type. Not validated against a protobuf enum because the :values
+  // target is deliberately protobuf-free; keep in sync with CelLiteDescriptor.FieldLiteDescriptor.
+  private static final int MIN_PROTO_TYPE_CODE = 1; // TYPE_DOUBLE
+  private static final int MAX_PROTO_TYPE_CODE = 18; // TYPE_SINT64
+  private static final int GROUP_PROTO_TYPE_CODE = 10; // Unsupported by CEL.
+
+  /** Protobuf field number of this hop. */
+  public abstract int fieldNumber();
+
+  /** Protobuf field name or map key of this hop. */
+  public abstract String fieldName();
+
+  /**
+   * Protobuf wire type code (1..18, except 10), {@link #CEL_MAP_TYPE_CODE}, or {@link
+   * #NO_TYPE_CODE}.
+   */
+  public abstract int typeCode();
+
+  /**
+   * Default value for this hop, or null if unspecified. When non-null, this must be an immutable
+   * CEL literal value.
+   */
+  public abstract @Nullable Object defaultValue();
+
+  /**
+   * Creates a presence-test qualifier hop.
+   *
+   * @param fieldNumber Protobuf field number. Takes {@code long} for compatibility with CEL's int64
+   *     constant representations.
+   * @param fieldName Protobuf field name.
+   */
+  public static SelectField create(long fieldNumber, String fieldName) {
+    checkArgument(
+        fieldNumber >= 1 && fieldNumber <= MAX_FIELD_NUMBER,
+        "Field number out of protobuf range: %s",
+        fieldNumber);
+    checkNotNull(fieldName);
+    return new AutoValue_SelectField(
+        (int) fieldNumber, fieldName, NO_TYPE_CODE, /* defaultValue= */ null);
+  }
+
+  /**
+   * Creates a fully-specified field selection hop with type code and optional default value.
+   *
+   * @param fieldNumber Protobuf field number. Takes {@code long} for compatibility with CEL's int64
+   *     constant representations.
+   * @param fieldName Protobuf field name.
+   * @param typeCode Protobuf wire type code or {@link #CEL_MAP_TYPE_CODE}. Takes {@code long} for
+   *     compatibility with CEL's int64 constant representations.
+   * @param defaultValue Default value for the field, or null if unspecified.
+   */
+  public static SelectField create(
+      long fieldNumber, String fieldName, long typeCode, @Nullable Object defaultValue) {
+    checkArgument(
+        fieldNumber >= 1 && fieldNumber <= MAX_FIELD_NUMBER,
+        "Field number out of protobuf range: %s",
+        fieldNumber);
+    checkNotNull(fieldName);
+    checkArgument(isSupportedTypeCode(typeCode), "Invalid protobuf type code: %s", typeCode);
+    return new AutoValue_SelectField((int) fieldNumber, fieldName, (int) typeCode, defaultValue);
+  }
+
+  /**
+   * Returns whether {@code typeCode} is a protobuf field type code CEL supports, or the {@link
+   * #CEL_MAP_TYPE_CODE} sentinel.
+   */
+  public static boolean isSupportedTypeCode(long typeCode) {
+    if (typeCode == CEL_MAP_TYPE_CODE) {
+      return true;
+    }
+    return typeCode >= MIN_PROTO_TYPE_CODE
+        && typeCode <= MAX_PROTO_TYPE_CODE
+        && typeCode != GROUP_PROTO_TYPE_CODE;
+  }
+
+  SelectField() {}
+}

common/src/test/java/dev/cel/common/values/BUILD.bazel

@@ -29,10 +29,13 @@ java_library(
         "//common/values:cel_value_provider",
         "//common/values:combined_cel_value_converter",
         "//common/values:combined_cel_value_provider",
+        "//common/values:optimized_select_traversal",
+        "//common/values:optimized_selectable",
         "//common/values:proto_message_lite_value",
         "//common/values:proto_message_lite_value_provider",
         "//common/values:proto_message_value",
         "//common/values:proto_message_value_provider",
+        "//common/values:select_field",
         "//protobuf:cel_lite_descriptor",
         "//testing/protos:test_all_types_cel_java_proto3",
         "@cel_spec//proto/cel/expr/conformance/proto2:test_all_types_java_proto",