Ensure chained optional field selection does not repeatedly wrap the optional type

Fixes #1083

PiperOrigin-RevId: 931223677

Author: l46kok

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

@@ -44,6 +44,7 @@
 import dev.cel.common.values.CelByteString;
 import dev.cel.common.values.NullValue;
 import dev.cel.compiler.CelCompiler;
+import dev.cel.expr.conformance.proto3.NestedTestAllTypes;
 import dev.cel.expr.conformance.proto3.TestAllTypes;
 import dev.cel.expr.conformance.proto3.TestAllTypes.NestedMessage;
 import dev.cel.parser.CelMacro;
@@ -603,6 +604,16 @@ public void optionalFieldSelection_onMap_returnsOptionalValue() throws Exception
     assertThat(result).hasValue(2L);
   }
 
+  @Test
+  public void optionalFieldSelection_onMap_chained_returnsSinglyWrappedOptional() throws Exception {
+    Cel cel = newCelBuilder().setResultType(OptionalType.create(SimpleType.STRING)).build();
+    CelAbstractSyntaxTree ast = compile(cel, "{'foo': {'bar': 'baz'}}.?foo.?bar");
+
+    Optional<String> result = (Optional<String>) cel.createProgram(ast).eval();
+
+    assertThat(result).hasValue("baz");
+  }
+
   @Test
   public void optionalFieldSelection_onProtoMessage_returnsOptionalEmpty() throws Exception {
     Cel cel =
@@ -619,6 +630,30 @@ public void optionalFieldSelection_onProtoMessage_returnsOptionalEmpty() throws
     assertThat(result).isEmpty();
   }
 
+  @Test
+  public void optionalFieldSelection_onProtoMessage_chained_returnsSinglyWrappedOptional()
+      throws Exception {
+    Cel cel =
+        newCelBuilder()
+            .setResultType(OptionalType.create(SimpleType.INT))
+            .addVar(
+                "msg", StructTypeReference.create(NestedTestAllTypes.getDescriptor().getFullName()))
+            .build();
+    CelAbstractSyntaxTree ast = compile(cel, "msg.?payload.?single_int32");
+
+    Optional<Long> result =
+        (Optional<Long>)
+            cel.createProgram(ast)
+                .eval(
+                    ImmutableMap.of(
+                        "msg",
+                        NestedTestAllTypes.newBuilder()
+                            .setPayload(TestAllTypes.newBuilder().setSingleInt32(5).build())
+                            .build()));
+
+    assertThat(result).hasValue(5L);
+  }
+
   @Test
   public void optionalFieldSelection_onProtoMessage_returnsOptionalValue() throws Exception {
     Cel cel =

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

@@ -783,8 +783,12 @@ private Optional<IntermediateResult> maybeEvalOptionalSelectField(
       }
 
       IntermediateResult result = evalFieldSelect(frame, expr, operand, field, false);
-      return Optional.of(
-          IntermediateResult.create(result.attribute(), Optional.of(result.value())));
+      // Ensure only one level of optional is wrapped when chaining optional field selections.
+      Object resultValue = result.value();
+      if (!(resultValue instanceof Optional)) {
+        resultValue = Optional.of(resultValue);
+      }
+      return Optional.of(IntermediateResult.create(result.attribute(), resultValue));
     }
 
     private IntermediateResult evalBoolean(ExecutionFrame frame, CelExpr expr, boolean strict)