Added support for modeling union types.

.changes/next-release/feature-AWSSDKforJavav2-34a662d.json

@@ -0,0 +1,6 @@
+{
+    "category": "AWS SDK for Java v2", 
+    "contributor": "", 
+    "type": "feature", 
+    "description": "Allow services to model structures with mutually exclusive fields (union types). Such structures have additional static constructors and the ability to query for which field is populated. Services which support this feature at launch: accessanalyzer, appconfig, appconfigdata, appmesh, connect, emrcontainers, evidently, grafana, groundstation, healthlake, inspector2, iottwinmaker, migrationhubstrategy, nimble, panorama, proton, rdsdata, redshiftdata, s3control, snowdevicemanagement, ssmincidents, transcribe, wisdom."
+}

codegen/src/main/java/software/amazon/awssdk/codegen/AddShapes.java

@@ -84,6 +84,7 @@ protected final ShapeModel generateShapeModel(String javaClassName, String shape
         shapeModel.withIsEventStream(shape.isEventstream());
         shapeModel.withIsEvent(shape.isEvent());
         shapeModel.withXmlNamespace(shape.getXmlNamespace());
+        shapeModel.withIsUnion(shape.isUnion());
 
         boolean hasHeaderMember = false;
         boolean hasStatusCodeMember = false;
@@ -188,6 +189,8 @@ private MemberModel generateMemberModel(String c2jMemberName, Member c2jMemberDe
         memberModel.setEventHeader(c2jMemberDefinition.isEventheader());
         memberModel.setEndpointDiscoveryId(c2jMemberDefinition.isEndpointdiscoveryid());
         memberModel.setXmlAttribute(c2jMemberDefinition.isXmlAttribute());
+        memberModel.setUnionEnumTypeName(namingStrategy.getUnionEnumTypeName(memberModel));
+
 
         // Pass the xmlNameSpace from the member reference
         if (c2jMemberDefinition.getXmlNamespace() != null) {

codegen/src/main/java/software/amazon/awssdk/codegen/model/intermediate/MemberModel.java

@@ -84,6 +84,8 @@ public class MemberModel extends DocumentationModel {
 
     private String beanStyleSetterName;
 
+    private String unionEnumTypeName;
+
     private boolean isJsonValue;
 
     private String timestampFormat;
@@ -481,7 +483,7 @@ public String getDeprecatedSetterDocumentation() {
     public String getDefaultConsumerFluentSetterDocumentation() {
         return (StringUtils.isNotBlank(documentation) ? documentation : defaultSetter().replace("%s", name) + "\n")
                + LF
-               + "This is a convenience that creates an instance of the {@link "
+               + "This is a convenience method that creates an instance of the {@link "
                + variable.getSimpleType()
                + ".Builder} avoiding the need to create one manually via {@link "
                + variable.getSimpleType()
@@ -509,6 +511,13 @@ public String getDefaultConsumerFluentSetterDocumentation() {
                + ")";
     }
 
+    public String getUnionConstructorDocumentation() {
+        return "Create an instance of this class with {@link #" + this.getFluentGetterMethodName() +
+               "()} initialized to the given value." +
+               LF + LF +
+               getSetterDocumentation();
+    }
+
     private String getParamDoc() {
         return LF
                + "@param "
@@ -726,4 +735,12 @@ public String getDeprecatedBeanStyleSetterMethodName() {
     public void setDeprecatedBeanStyleSetterMethodName(String deprecatedBeanStyleSetterMethodName) {
         this.deprecatedBeanStyleSetterMethodName = deprecatedBeanStyleSetterMethodName;
     }
+
+    public String getUnionEnumTypeName() {
+        return unionEnumTypeName;
+    }
+
+    public void setUnionEnumTypeName(String unionEnumTypeName) {
+        this.unionEnumTypeName = unionEnumTypeName;
+    }
 }

codegen/src/main/java/software/amazon/awssdk/codegen/model/intermediate/ShapeModel.java

@@ -15,6 +15,7 @@
 
 package software.amazon.awssdk.codegen.model.intermediate;
 
+import static software.amazon.awssdk.codegen.internal.Constant.LF;
 import static software.amazon.awssdk.codegen.internal.Constant.REQUEST_CLASS_SUFFIX;
 import static software.amazon.awssdk.codegen.internal.Constant.RESPONSE_CLASS_SUFFIX;
 import static software.amazon.awssdk.codegen.internal.DocumentationUtils.removeFromEnd;
@@ -71,6 +72,8 @@ public class ShapeModel extends DocumentationModel implements HasDeprecation {
 
     private boolean document;
 
+    private boolean union;
+
     public ShapeModel() {
     }
 
@@ -526,6 +529,16 @@ public String getDocumentationShapeName() {
         }
     }
 
+    public String getUnionTypeGetterDocumentation() {
+        return "Retrieve an enum value representing which member of this object is populated. "
+               + LF + LF
+               + "When this class is returned in a service response, this will be {@link Type#UNKNOWN_TO_SDK_VERSION} if the "
+               + "service returned a member that is only known to a newer SDK version."
+               + LF + LF
+               + "When this class is created directly in your code, this will be {@link Type#UNKNOWN_TO_SDK_VERSION} if zero "
+               + "members are set, and {@code null} if more than one member is set.";
+    }
+
     @Override
     public String toString() {
         return shapeName;
@@ -617,4 +630,12 @@ public ShapeModel withIsDocument(boolean document) {
         this.document = document;
         return this;
     }
+
+    public boolean isUnion() {
+        return union;
+    }
+
+    public void withIsUnion(boolean union) {
+        this.union = union;
+    }
 }

codegen/src/main/java/software/amazon/awssdk/codegen/model/service/Shape.java

@@ -74,6 +74,8 @@ public class Shape {
 
     private boolean document;
 
+    private boolean union;
+
     public boolean isFault() {
         return fault;
     }
@@ -318,4 +320,11 @@ public void setDocument(boolean document) {
         this.document = document;
     }
 
+    public boolean isUnion() {
+        return union;
+    }
+
+    public void setUnion(boolean union) {
+        this.union = union;
+    }
 }

codegen/src/main/java/software/amazon/awssdk/codegen/naming/DefaultNamingStrategy.java

@@ -363,6 +363,11 @@ public String getSdkFieldFieldName(MemberModel memberModel) {
         return screamCase(memberModel.getName()) + "_FIELD";
     }
 
+    @Override
+    public String getUnionEnumTypeName(MemberModel memberModel) {
+        return screamCase(memberModel.getName());
+    }
+
     private String rewriteInvalidMemberName(String memberName, Shape parentShape) {
         if (isJavaKeyword(memberName) || isDisallowedNameForShape(memberName, parentShape)) {
             return Utils.unCapitalize(memberName + CONFLICTING_NAME_SUFFIX);
@@ -372,6 +377,11 @@ private String rewriteInvalidMemberName(String memberName, Shape parentShape) {
     }
 
     private boolean isDisallowedNameForShape(String name, Shape parentShape) {
+        // Reserve the name "type" for union shapes.
+        if (parentShape.isUnion() && name.equals("type")) {
+            return true;
+        }
+
         if (parentShape.isException()) {
             return RESERVED_EXCEPTION_METHOD_NAMES.contains(name);
         } else {

codegen/src/main/java/software/amazon/awssdk/codegen/naming/NamingStrategy.java

@@ -147,6 +147,14 @@ public interface NamingStrategy {
      */
     String getSdkFieldFieldName(MemberModel memberModel);
 
+    /**
+     * Returns the name of the provided member as if it will be included in an enum (as in, when the parent shape is a union
+     * and we need to create an enum with each member name in it).
+     *
+     * @param memberModel Member to generate the union enum type name for.
+     */
+    String getUnionEnumTypeName(MemberModel memberModel);
+
     /**
      * Names a method that would check for existence of the member in the response.
      *

codegen/src/main/java/software/amazon/awssdk/codegen/poet/model/AbstractMemberSetters.java

@@ -201,13 +201,26 @@ private MethodSpec.Builder setterDeclaration(String methodName, ParameterSpec pa
     }
 
     private CodeBlock copySetterBody(String copyAssignment, String regularAssignment, String copyMethodName) {
+        CodeBlock.Builder body = CodeBlock.builder();
+
+        if (shapeModel.isUnion()) {
+            body.addStatement("Object oldValue = this.$N", fieldName());
+        }
+
         Optional<ClassName> copierClass = serviceModelCopiers.copierClassFor(memberModel);
 
-        return copierClass.map(className -> CodeBlock.builder().addStatement(copyAssignment,
-                                                                             fieldName(),
-                                                                             className,
-                                                                             copyMethodName)
-                                                     .build())
-                          .orElseGet(() -> CodeBlock.builder().addStatement(regularAssignment, fieldName()).build());
+        if (copierClass.isPresent()) {
+            body.addStatement(copyAssignment, fieldName(), copierClass.get(), copyMethodName);
+        } else {
+            body.addStatement(regularAssignment, fieldName());
+        }
+
+        if (shapeModel.isUnion()) {
+            body.addStatement("handleUnionValueChange(Type.$N, oldValue, this.$N)",
+                              memberModel.getUnionEnumTypeName(),
+                              fieldName());
+        }
+
+        return body.build();
     }
 }