Adding AWS CFN Trait: cfnDefaultValue (#1285)

* cfnDefaultValue trait definition added

docs/source/1.0/spec/aws/aws-cloudformation.rst

@@ -640,6 +640,68 @@ The following example defines a CloudFormation resource that has the
         fooAlias: String
     }
 
+.. smithy-trait:: aws.cloudformation#cfnDefaultValue
+.. _aws.cloudformation#cfnDefaultValue-trait:
+
+----------------------------------------
+``aws.cloudformation#cfnDefaultValue`` trait
+----------------------------------------
+
+Summary
+    Indicates that the member annotated has a default value for the resource.
+Trait selector
+    ``resource > operation -[output]-> structure > member``
+
+    *Only applicable to members of ``@output`` operations*
+Value type
+    Annotation trait
+
+Given the following example, because the ``fooAlias``
+member is annotated with ``cfnDefaultValue``, it can be derived
+that the ``fooAlias`` member has a default value for this resource.
+
+.. code-block:: smithy
+
+    namespace smithy.example
+
+    use aws.cloudformation#cfnDefaultValue
+    use aws.cloudformation#cfnResource
+
+    @cfnResource
+    resource Foo {
+        identifiers: {
+            fooId: String,
+        },
+        read: GetFoo,
+    }
+
+    @readonly
+    @http(method: "GET", uri: "/foos/{fooId}", code: 200)
+    operation GetFoo {
+        input: GetFooRequest,
+        output: GetFooResponse,
+    }
+
+    @input
+    structure GetFooRequest {
+        @httpLabel
+        @required
+        fooId: String,
+
+        fooAlias: String,
+    }
+
+    @output
+    structure GetFooResponse {
+        fooId: String,
+
+        @cfnDefaultValue
+        fooAlias: String,
+
+        @httpResponseCode
+        responseCode: Integer,
+    }
+
 
 -------------
 Example model
@@ -656,6 +718,7 @@ Given the following model,
 
     namespace smithy.example
 
+    use aws.cloudformation#cfnDefaultValue
     use aws.cloudformation#cfnAdditionalIdentifier
     use aws.cloudformation#cfnExcludeProperty
     use aws.cloudformation#cfnMutability
@@ -727,10 +790,11 @@ Given the following model,
         @cfnMutability("read")
         updatedAt: Timestamp
 
-        fooAlias: String
-        createProperty: ComplexProperty
-        mutableProperty: ComplexProperty
-        readProperty: ComplexProperty
+        @cfnDefaultValue
+        fooAlias: String,
+        createProperty: ComplexProperty,
+        mutableProperty: ComplexProperty,
+        readProperty: ComplexProperty,
     }
 
     @idempotent

smithy-aws-cloudformation-traits/src/main/java/software/amazon/smithy/aws/cloudformation/traits/CfnDefaultValueTrait.java

@@ -0,0 +1,43 @@
+/*
+ * Copyright 2022 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License").
+ * You may not use this file except in compliance with the License.
+ * A copy of the License is located at
+ *
+ *  http://aws.amazon.com/apache2.0
+ *
+ * or in the "license" file accompanying this file. This file is distributed
+ * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
+ * express or implied. See the License for the specific language governing
+ * permissions and limitations under the License.
+ */
+
+package software.amazon.smithy.aws.cloudformation.traits;
+
+import software.amazon.smithy.model.node.Node;
+import software.amazon.smithy.model.node.ObjectNode;
+import software.amazon.smithy.model.shapes.ShapeId;
+import software.amazon.smithy.model.traits.AnnotationTrait;
+
+/**
+ * Indicates that the CloudFormation property generated from this member has a
+ * default value for this resource.
+ */
+public final class CfnDefaultValueTrait extends AnnotationTrait {
+    public static final ShapeId ID = ShapeId.from("aws.cloudformation#cfnDefaultValue");
+
+    public CfnDefaultValueTrait(ObjectNode node) {
+        super(ID, node);
+    }
+
+    public CfnDefaultValueTrait() {
+        this(Node.objectNode());
+    }
+
+    public static final class Provider extends AnnotationTrait.Provider<CfnDefaultValueTrait> {
+        public Provider() {
+            super(ID, CfnDefaultValueTrait::new);
+        }
+    }
+}

smithy-aws-cloudformation-traits/src/main/resources/META-INF/services/software.amazon.smithy.model.traits.TraitService

@@ -1,3 +1,4 @@
+software.amazon.smithy.aws.cloudformation.traits.CfnDefaultValueTrait$Provider
 software.amazon.smithy.aws.cloudformation.traits.CfnAdditionalIdentifierTrait$Provider
 software.amazon.smithy.aws.cloudformation.traits.CfnExcludePropertyTrait$Provider
 software.amazon.smithy.aws.cloudformation.traits.CfnMutabilityTrait$Provider

smithy-aws-cloudformation-traits/src/main/resources/META-INF/smithy/aws.cloudformation.smithy

@@ -29,11 +29,21 @@ string cfnName
     conflicts: [
         cfnAdditionalIdentifier,
         cfnMutability,
+        cfnDefaultValue
     ],
     breakingChanges: [{change: "add"}]
 )
 structure cfnExcludeProperty {}
 
+/// Indicates that a structure member has a default value
+/// for the property of the CloudFormation resource.
+@unstable
+@trait(
+    selector: "resource > operation -[input, output]-> structure > member",
+    conflicts: [cfnExcludeProperty]
+)
+structure cfnDefaultValue {}
+
 /// Indicates an explicit CloudFormation mutability of the structure member
 /// when part of a CloudFormation resource.
 @unstable

smithy-aws-cloudformation-traits/src/test/java/software/amazon/smithy/aws/cloudformation/traits/CfnDefaultValueTraitTest.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2022 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License").
+ * You may not use this file except in compliance with the License.
+ * A copy of the License is located at
+ *
+ *  http://aws.amazon.com/apache2.0
+ *
+ * or in the "license" file accompanying this file. This file is distributed
+ * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
+ * express or implied. See the License for the specific language governing
+ * permissions and limitations under the License.
+ */
+
+package software.amazon.smithy.aws.cloudformation.traits;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.Test;
+import software.amazon.smithy.model.Model;
+import software.amazon.smithy.model.shapes.ShapeId;
+
+public final class CfnDefaultValueTraitTest {
+
+    @Test
+    public void detectsDefaultValue() {
+        Model result = Model.assembler()
+                .discoverModels(getClass().getClassLoader())
+                .addImport(getClass().getResource("test-service.smithy"))
+                .assemble()
+                .unwrap();
+
+        assertTrue(result.getShape(ShapeId.from("smithy.example#GetFooResponse$fooId"))
+                .flatMap(shape -> shape.getTrait(CfnDefaultValueTrait.class))
+                .isPresent());
+    }
+}

smithy-aws-cloudformation-traits/src/test/resources/software/amazon/smithy/aws/cloudformation/traits/test-service.smithy

@@ -6,6 +6,7 @@ use aws.cloudformation#cfnResource
 use aws.cloudformation#cfnAdditionalIdentifier
 use aws.cloudformation#cfnExcludeProperty
 use aws.cloudformation#cfnMutability
+use aws.cloudformation#cfnDefaultValue
 
 service TestService {
     version: "2020-07-02",
@@ -55,6 +56,7 @@ structure GetFooRequest {
 }
 
 structure GetFooResponse {
+    @cfnDefaultValue
     fooId: FooId,
 
     fooValidReadProperty: String,