Support optional field selection in SelectOptimizer and the planner runtime

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

@@ -51,6 +51,23 @@ static Object qualify(Object target, ImmutableList<SelectField> fields, int from
     return current;
   }
 
+  /**
+   * Presence tests every field in {@code fields} in turn, returning the terminal value or empty if
+   * any field is absent.
+   */
+  public static Optional<Object> find(Object target, ImmutableList<SelectField> fields) {
+    Optional<Object> current = Optional.empty();
+    Object next = target;
+    for (int i = 0; i < fields.size(); i++) {
+      current = navigateField(next, fields.get(i));
+      if (!current.isPresent()) {
+        return Optional.empty();
+      }
+      next = current.get();
+    }
+    return current;
+  }
+
   /**
    * Presence tests the terminal field of {@code fields}, navigating through all preceding fields.
    */
@@ -77,9 +94,6 @@ public static boolean hasField(Object target, ImmutableList<SelectField> fields)
   // StructValue 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);
     }
@@ -99,9 +113,6 @@ private static Object qualifyField(Object target, SelectField field) {
   // StructValue 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);
     }
@@ -114,9 +125,6 @@ private static Optional<Object> navigateField(Object target, SelectField field)
   // StructValue 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);
     }

common/src/test/java/dev/cel/common/values/OptimizedSelectTraversalTest.java

@@ -271,25 +271,28 @@ public void hasField_unsupportedTarget_throwsException() {
   }
 
   @Test
-  public void qualify_errorValue_propagatesError() {
-    ErrorValue error = ErrorValue.create(1L, new RuntimeException("test error"));
-    ImmutableList<SelectField> fields =
-        ImmutableList.of(SelectField.create(1L, "field1"), SelectField.create(2L, "field2"));
-
-    Object result = OptimizedSelectTraversal.qualify(error, fields);
+  public void find_emptyFields_returnsEmpty() {
+    Optional<Object> result = OptimizedSelectTraversal.find(new Object(), ImmutableList.of());
 
-    assertThat(result).isSameInstanceAs(error);
+    assertThat(result).isEmpty();
   }
 
   @Test
-  public void hasField_errorValue_returnsFalse() {
-    ErrorValue error = ErrorValue.create(1L, new RuntimeException("test error"));
+  public void find_nestedFields(
+      @TestParameter TargetType targetType, @TestParameter NestedPresenceTestCase testCase) {
+    Object target = targetType.createNestedTarget(testCase.innerData);
     ImmutableList<SelectField> fields =
-        ImmutableList.of(SelectField.create(1L, "field1"), SelectField.create(2L, "field2"));
+        ImmutableList.of(
+            SelectField.create(1L, testCase.outerField),
+            SelectField.create(2L, testCase.innerField));
 
-    boolean result = OptimizedSelectTraversal.hasField(error, fields);
+    Optional<Object> result = OptimizedSelectTraversal.find(target, fields);
 
-    assertThat(result).isFalse();
+    if (testCase.expected) {
+      assertThat(result).hasValue("nested_val");
+    } else {
+      assertThat(result).isEmpty();
+    }
   }
 
   @SuppressWarnings("Immutable")

optimizer/src/main/java/dev/cel/optimizer/optimizers/DefaultOptimizerConstants.java

@@ -47,7 +47,13 @@ final class DefaultOptimizerConstants {
           .build();
 
   static final String CEL_ATTRIBUTE_FUNCTION_NAME = "cel.@attribute";
+  static final String CEL_OPTIONAL_ATTRIBUTE_FUNCTION_NAME = "cel.@optionalAttribute";
   static final String CEL_HAS_FIELD_FUNCTION_NAME = "cel.@hasField";
+  static final ImmutableSet<String> SELECT_OPTIMIZED_FUNCTION_NAMES =
+      ImmutableSet.of(
+          CEL_ATTRIBUTE_FUNCTION_NAME,
+          CEL_OPTIONAL_ATTRIBUTE_FUNCTION_NAME,
+          CEL_HAS_FIELD_FUNCTION_NAME);
 
   private DefaultOptimizerConstants() {}
 }