Fix CEL bindings for maps (#278)

This fixes the variable binding to `this` for maps. Previously, the
binding was using a map of the custom value abstraction `ObjectValue`
that we use in protovalidate-java. This `Value` class has no relation at
all to CEL-Java's `Val` object. So, using it as a variable binding does
not work because CEL-Java doesn't know how to interpret it.

This adds an additional `mapValueAsObject` function to return a map of
`Object`s for the binding. Note this not ideal, but should be sufficient
for now. Further context in the comments.

Author: smaye81

conformance/expected-failures.yaml

@@ -1,17 +0,0 @@
-custom_rules:
-  - field_expression/map/enum/invalid
-  - field_expression/map/enum/valid
-  - field_expression/map/message/invalid
-  - field_expression/map/message/valid
-  - field_expression/map/bool/valid
-  - field_expression/map/bool/invalid
-  - field_expression/map/string/valid
-  - field_expression/map/string/invalid
-  - field_expression/map/int32/valid
-  - field_expression/map/int32/invalid
-  - field_expression/map/uint32/valid
-  - field_expression/map/uint32/invalid
-  - field_expression/map/int64/valid
-  - field_expression/map/int64/invalid
-  - field_expression/map/uint64/valid
-  - field_expression/map/uint64/invalid

src/main/java/build/buf/protovalidate/ObjectValue.java

@@ -64,6 +64,9 @@ public Message messageValue() {
   @Override
   public <T> T value(Class<T> clazz) {
     Descriptors.FieldDescriptor.Type type = fieldDescriptor.getType();
+    if (fieldDescriptor.isMapField()) {
+      return clazz.cast(mapValueAsObject());
+    }
     if (!fieldDescriptor.isRepeated()
         && (type == Descriptors.FieldDescriptor.Type.UINT32
             || type == Descriptors.FieldDescriptor.Type.UINT64
@@ -93,6 +96,38 @@ public List<Value> repeatedValue() {
     return out;
   }
 
+  // TODO - This should be refactored at some point.
+  //
+  // This is essentially the same functionality as `mapValue` except that it
+  // returns a Map of Objects rather than a Map of protovalidate-java Values.
+  // It is used for binding to a CEL variable (i.e. `this`).
+  // Trying to bind a Map of Values to a CEL variable does not work because
+  // CEL-Java doesn't know how to interpret that proprietary Value object.
+  //
+  // Ideally, we should be using CEL-Java's org.projectnessie.cel.common.types.ref.Val
+  // type instead of our own custom Value abstraction. However, since we are evaluating
+  // Java CEL implementations, we should probably wait until that decision is made before
+  // making such a large refactor. This should suffice as a stopgap until then.
+  private Map<Object, Object> mapValueAsObject() {
+    List<AbstractMessage> input =
+        value instanceof List
+            ? (List<AbstractMessage>) value
+            : Collections.singletonList((AbstractMessage) value);
+
+    Descriptors.FieldDescriptor keyDesc = fieldDescriptor.getMessageType().findFieldByNumber(1);
+    Descriptors.FieldDescriptor valDesc = fieldDescriptor.getMessageType().findFieldByNumber(2);
+    Map<Object, Object> out = new HashMap<>(input.size());
+
+    for (AbstractMessage entry : input) {
+      Object keyValue = entry.getField(keyDesc);
+      Object valValue = entry.getField(valDesc);
+
+      out.put(keyValue, valValue);
+    }
+
+    return out;
+  }
+
   @Override
   public Map<Value, Value> mapValue() {
     List<AbstractMessage> input =