Fix issue where we emitted events twice

ModelAssembler event listeners were receiving events twice in some cases,
causing events to appear twice when running the CLI/Gradle/etc.

Author: mtdowling

smithy-model/src/main/java/software/amazon/smithy/model/loader/ModelValidator.java

@@ -24,7 +24,6 @@
 import java.util.Set;
 import java.util.function.Consumer;
 import java.util.stream.Collectors;
-import java.util.stream.Stream;
 import software.amazon.smithy.model.Model;
 import software.amazon.smithy.model.SourceException;
 import software.amazon.smithy.model.SourceLocation;
@@ -194,16 +193,20 @@ public Validator createValidator() {
                 return coreEvents;
             }
 
-            Stream<ValidationEvent> eventStream = Stream.concat(
-                    includeEvents.stream(),
-                    modelValidators.parallelStream().flatMap(validator -> validator.validate(model).stream()));
-            List<ValidationEvent> result = eventStream
+            List<ValidationEvent> result = modelValidators.parallelStream()
+                    .flatMap(validator -> validator.validate(model).stream())
                     .filter(ModelValidator::filterPrelude)
                     .map(event -> suppressEvent(model, event, modelSuppressions))
                     // Emit events as they occur during validation.
                     .peek(eventListener)
                     .collect(Collectors.toList());
 
+            for (ValidationEvent event : includeEvents) {
+                if (ModelValidator.filterPrelude(event)) {
+                    result.add(suppressEvent(model, event, modelSuppressions));
+                }
+            }
+
             // Add in events encountered while building up validators and suppressions.
             result.addAll(coreEvents);
 

smithy-model/src/test/java/software/amazon/smithy/model/loader/ModelAssemblerTest.java

@@ -932,4 +932,20 @@ public void forwardReferencesAreOrdered() {
                             ShapeId.from("smithy.example#Error5"),
                             ShapeId.from("smithy.example#Error6")));
     }
+
+    @Test
+    public void doesNotEmitWarningsTwice() {
+        List<ValidationEvent> events = new ArrayList<>();
+        Model.assembler()
+                .addUnparsedModel("foo.smithy", "$version: \"1.0\"\n")
+                .validationEventListener(e -> {
+                    if (e.getId().equals(Validator.MODEL_DEPRECATION)) {
+                        events.add(e);
+                    }
+                })
+                .assemble()
+                .unwrap();
+
+        assertThat(events, hasSize(1));
+    }
 }