Add option to enable prelude serialization

smithy-model/src/main/java/software/amazon/smithy/model/shapes/SmithyIdlModelSerializer.java

@@ -64,7 +64,13 @@ public final class SmithyIdlModelSerializer {
 
     private SmithyIdlModelSerializer(Builder builder) {
         metadataFilter = builder.metadataFilter;
-        shapeFilter = builder.shapeFilter.and(FunctionalUtils.not(Prelude::isPreludeShape));
+        // If prelude serializing has been enabled, only use the given shape filter.
+        if (builder.serializePrelude) {
+            shapeFilter = builder.shapeFilter;
+        // Default to using the given shape filter and filtering prelude shapes.
+        } else {
+            shapeFilter = builder.shapeFilter.and(FunctionalUtils.not(Prelude::isPreludeShape));
+        }
         // Never serialize synthetic traits.
         traitFilter = builder.traitFilter.and(FunctionalUtils.not(Trait::isSynthetic));
         basePath = builder.basePath;
@@ -236,6 +242,7 @@ public static final class Builder implements SmithyBuilder<SmithyIdlModelSeriali
         private Predicate<Trait> traitFilter = FunctionalUtils.alwaysTrue();
         private Function<Shape, Path> shapePlacer = SmithyIdlModelSerializer::placeShapesByNamespace;
         private Path basePath = null;
+        private boolean serializePrelude = false;
 
         public Builder() {}
 
@@ -302,6 +309,16 @@ public Builder basePath(Path basePath) {
             return this;
         }
 
+        /**
+         * Enables serializing shapes in the Smithy prelude.
+         * Defaults to false.
+         * @return Returns the builder.
+         */
+        public Builder serializePrelude() {
+            this.serializePrelude = true;
+            return this;
+        }
+
         @Override
         public SmithyIdlModelSerializer build() {
             return new SmithyIdlModelSerializer(this);

smithy-model/src/test/java/software/amazon/smithy/model/shapes/SmithyIdlModelSerializerTest.java

@@ -78,6 +78,7 @@ public void filtersShapes() {
         assertThat(serialized, hasKey(Paths.get("ns.structures.smithy")));
         assertThat(serialized.get(Paths.get("ns.structures.smithy")),
                 containsString("namespace ns.structures"));
+        assertThat(serialized, not(hasKey(Paths.get("smithy.api.smithy"))));
     }
 
     @Test
@@ -168,4 +169,17 @@ public void transientTraitsAreNotSerialized() {
         assertThat(results.get(Paths.get("com.foo.smithy")),
                    not(containsString(OriginalShapeIdTrait.ID.toString())));
     }
+
+    @Test
+    public void canEnableSerializingPrelude() {
+        Model model = Model.assembler()
+                .addImport(getClass().getResource("idl-serialization/test-model.json"))
+                .assemble()
+                .unwrap();
+        SmithyIdlModelSerializer serializer = SmithyIdlModelSerializer.builder()
+                .serializePrelude()
+                .build();
+        Map<Path, String> serialized = serializer.serialize(model);
+        assertThat(serialized.get(Paths.get("smithy.api.smithy")), containsString("namespace smithy.api"));
+    }
 }