Return optional.none() for out-of-range int64 optional list indexes

extensions/src/main/java/dev/cel/extensions/BUILD.bazel

@@ -362,6 +362,7 @@ java_library(
         "//runtime:function_binding",
         "//runtime:lite_runtime",
         "//runtime:runtime_equality",
+        "//runtime:runtime_helpers",
         "@maven//:com_google_errorprone_error_prone_annotations",
         "@maven//:com_google_guava_guava",
         "@maven//:com_google_protobuf_protobuf_java",
@@ -382,6 +383,7 @@ cel_android_library(
         "//runtime:function_binding_android",
         "//runtime:lite_runtime_android",
         "//runtime:runtime_equality_android",
+        "//runtime:runtime_helpers_android",
         "@maven//:com_google_errorprone_error_prone_annotations",
         "@maven_android//:com_google_guava_guava",
         "@maven_android//:com_google_protobuf_protobuf_javalite",

extensions/src/main/java/dev/cel/extensions/CelOptionalRuntimeLibrary.java

@@ -17,7 +17,6 @@
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Iterables;
-import com.google.common.primitives.Ints;
 import com.google.common.primitives.UnsignedLong;
 import com.google.errorprone.annotations.Immutable;
 import com.google.protobuf.MessageLite;
@@ -30,6 +29,7 @@
 import dev.cel.runtime.CelInternalLiteRuntimeLibrary;
 import dev.cel.runtime.CelLiteRuntimeBuilder;
 import dev.cel.runtime.RuntimeEquality;
+import dev.cel.runtime.RuntimeHelpers;
 import java.time.Duration;
 import java.time.Instant;
 import java.util.Collection;
@@ -222,10 +222,7 @@ public ImmutableSet<CelFunctionBinding> newFunctionBindings(RuntimeEquality runt
         CelFunctionBinding.fromOverloads(
             Operator.OPTIONAL_INDEX.getFunction(),
             CelFunctionBinding.from(
-                "list_optindex_optional_int",
-                List.class,
-                Long.class,
-                CelOptionalRuntimeLibrary::indexList),
+                "list_optindex_optional_int", List.class, Long.class, RuntimeHelpers::optIndexList),
             CelFunctionBinding.from(
                 "optional_list_optindex_optional_int",
                 Optional.class,
@@ -312,20 +309,12 @@ private static Object indexOptionalMap(
     return runtimeEquality.findInMap(map, key);
   }
 
-  private static Object indexList(List<?> list, long index) {
-    int castIndex = Ints.checkedCast(index);
-    if (castIndex < 0 || castIndex >= list.size()) {
-      return Optional.empty();
-    }
-    return Optional.of(list.get(castIndex));
-  }
-
   private static Object indexOptionalList(Optional<?> optionalList, long index) {
     if (!optionalList.isPresent()) {
       return Optional.empty();
     }
     List<?> list = (List<?>) optionalList.get();
-    return indexList(list, index);
+    return RuntimeHelpers.optIndexList(list, index);
   }
 
   private static Object listOptionalFirst(Collection<?> list) {

extensions/src/test/java/dev/cel/extensions/CelOptionalLibraryTest.java

@@ -1123,6 +1123,38 @@ public void optionalIndex_onOptionalList_returnsOptionalValue() throws Exception
     assertThat(result).isEqualTo(Optional.of("hello"));
   }
 
+  @Test
+  public void optionalIndex_outOfBounds_returnsOptionalEmpty(
+      @TestParameter({
+            "l[?-1]",
+            "l[?1]",
+            "l[?4294967296]",
+            "l[?-4294967296]",
+            "optl[?4294967296]",
+            "optl[4294967296]"
+          })
+          String expression)
+      throws Exception {
+    TestCel cel =
+        newCelBuilder()
+            .addVar("l", ListType.create(SimpleType.STRING))
+            .addVar("optl", OptionalType.create(ListType.create(SimpleType.STRING)))
+            .setResultType(OptionalType.create(SimpleType.STRING))
+            .build();
+    CelAbstractSyntaxTree ast = compile(cel, expression);
+
+    Object result =
+        cel.createProgram(ast)
+            .eval(
+                ImmutableMap.of(
+                    "l",
+                    ImmutableList.of("hello"),
+                    "optl",
+                    Optional.of(ImmutableList.of("hello"))));
+
+    assertThat(result).isEqualTo(Optional.empty());
+  }
+
   @Test
   public void optionalIndex_onListWithUnknownInput_returnsUnknownResult() throws Exception {
     TestCel cel =

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

@@ -140,6 +140,14 @@ public static <A> A indexList(List<A> list, Number index) {
     return list.get((int) longIndex);
   }
 
+  /** Returns the element of {@code list} at {@code index}, or empty if it's out of bounds. */
+  public static Optional<Object> optIndexList(List<?> list, long index) {
+    if (index < 0 || index >= list.size()) {
+      return Optional.empty();
+    }
+    return Optional.of(list.get((int) index));
+  }
+
   // Integer Arithmetic
   // ==================
   //