Add Operation helper method to include service errors

smithy-model/src/main/java/software/amazon/smithy/model/knowledge/OperationIndex.java

@@ -18,11 +18,11 @@
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.HashMap;
+import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
 import java.util.Set;
-import java.util.TreeSet;
 import software.amazon.smithy.model.Model;
 import software.amazon.smithy.model.shapes.MemberShape;
 import software.amazon.smithy.model.shapes.OperationShape;
@@ -189,7 +189,7 @@ public List<StructureShape> getErrors(ToShapeId operation) {
      * @return Returns the list of error structures, or an empty list.
      */
     public List<StructureShape> getErrors(ToShapeId service, ToShapeId operation) {
-        Set<StructureShape> result = new TreeSet<>(getErrors(service));
+        Set<StructureShape> result = new LinkedHashSet<>(getErrors(service));
         result.addAll(getErrors(operation));
         return new ArrayList<>(result);
     }

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

@@ -17,9 +17,12 @@
 
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Objects;
 import java.util.Optional;
+import java.util.Set;
+import software.amazon.smithy.model.knowledge.OperationIndex;
 import software.amazon.smithy.utils.ListUtils;
 import software.amazon.smithy.utils.ToSmithyBuilder;
 
@@ -79,18 +82,43 @@ public Optional<ShapeId> getOutput() {
     }
 
     /**
-     * <p>Gets a list of the error shape IDs that can be encountered.</p>
+     * <p>Gets a list of the error shape IDs bound directly to the operation
+     * that can be encountered.
+     *
+     * <p>This DOES NOT include errors that are common to a service. Operations
+     * can be bound to multiple services, so common service errors cannot be
+     * returned by this method. Use {@link #getErrors(ServiceShape)} or
+     * {@link OperationIndex#getErrors(ToShapeId, ToShapeId)} to get all of the
+     * errors an operation can encounter when used within a service.</p>
      *
      * <p>Each returned {@link ShapeId} must resolve to a
      * {@link StructureShape} that is targeted by an error trait; however,
      * this is only guaranteed after a model is validated.</p>
      *
      * @return Returns the errors.
+     * @see #getErrors(ServiceShape)
+     * @see OperationIndex#getErrors(ToShapeId, ToShapeId)
      */
     public List<ShapeId> getErrors() {
         return errors;
     }
 
+    /**
+     * <p>Gets a list of the error shape IDs the operation can encounter,
+     * including any common errors of a service.
+     *
+     * <p>No validation is performed here to ensure that the operation is
+     * actually bound to the given service shape.
+     *
+     * @return Returns the errors.
+     * @see OperationIndex#getErrors(ToShapeId, ToShapeId)
+     */
+    public List<ShapeId> getErrors(ServiceShape service) {
+        Set<ShapeId> result = new LinkedHashSet<>(service.getErrors());
+        result.addAll(getErrors());
+        return new ArrayList<>(result);
+    }
+
     @Override
     public boolean equals(Object other) {
         if (!super.equals(other)) {
@@ -109,7 +137,7 @@ public boolean equals(Object other) {
     public static final class Builder extends AbstractShapeBuilder<Builder, OperationShape> {
         private ShapeId input;
         private ShapeId output;
-        private List<ShapeId> errors = new ArrayList<>();
+        private final List<ShapeId> errors = new ArrayList<>();
 
         @Override
         public ShapeType getShapeType() {

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

@@ -0,0 +1,46 @@
+/*
+ * Copyright 2021 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.model.shapes;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.contains;
+
+import java.util.List;
+import org.junit.jupiter.api.Test;
+
+public class OperationShapeTest {
+    @Test
+    public void combinesErrorsWithServiceErrors() {
+        ServiceShape service = ServiceShape.builder()
+                .id("com.foo#Example")
+                .version("x")
+                .addError("com.foo#Common1")
+                .addError(ShapeId.from("com.foo#Common2"))
+                .build();
+
+        OperationShape operation = OperationShape.builder()
+                .id("com.foo#Operation")
+                .addError("com.foo#OperationError")
+                .build();
+
+        List<ShapeId> allErrors = operation.getErrors(service);
+
+        assertThat(allErrors, contains(
+                ShapeId.from("com.foo#Common1"),
+                ShapeId.from("com.foo#Common2"),
+                ShapeId.from("com.foo#OperationError")));
+    }
+}