Add NodeValidationVisitor plugin for @Uniqueitems

smithy-model/src/main/java/software/amazon/smithy/model/validation/node/NodeValidatorPlugin.java

@@ -64,7 +64,8 @@ static List<NodeValidatorPlugin> getBuiltins() {
                 new PatternTraitPlugin(),
                 new RangeTraitPlugin(),
                 new StringEnumPlugin(),
-                new StringLengthPlugin());
+                new StringLengthPlugin(),
+                new UniqueItemsPlugin());
     }
 
     /**

smithy-model/src/main/java/software/amazon/smithy/model/validation/node/UniqueItemsPlugin.java

@@ -0,0 +1,47 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package software.amazon.smithy.model.validation.node;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.LinkedHashSet;
+import java.util.List;
+import java.util.Set;
+import software.amazon.smithy.model.node.ArrayNode;
+import software.amazon.smithy.model.node.Node;
+import software.amazon.smithy.model.shapes.CollectionShape;
+import software.amazon.smithy.model.shapes.Shape;
+import software.amazon.smithy.model.traits.UniqueItemsTrait;
+
+/**
+ * Validates that items in lists with the `@uniqueItems` trait are unique.
+ */
+final class UniqueItemsPlugin extends MemberAndShapeTraitPlugin<CollectionShape, ArrayNode, UniqueItemsTrait> {
+    UniqueItemsPlugin() {
+        super(CollectionShape.class, ArrayNode.class, UniqueItemsTrait.class);
+    }
+
+    @Override
+    protected void check(Shape shape, UniqueItemsTrait trait, ArrayNode value, Context context, Emitter emitter) {
+        Set<Node> uniqueNodes = new HashSet<>(value.getElements());
+        if (uniqueNodes.size() != value.size()) {
+            List<Node> duplicateNodes = new ArrayList<>(value.getElements());
+            for (Node uniqueNode : uniqueNodes) {
+                // Collections remove the first encountered entry, so our unique
+                // nodes through a set will leave behind any duplicates.
+                duplicateNodes.remove(uniqueNode);
+            }
+
+            Set<String> duplicateValues = new LinkedHashSet<>();
+            for (Node duplicateNode : duplicateNodes) {
+                duplicateValues.add(duplicateNode.toString());
+            }
+            emitter.accept(value, String.format(
+                    "Value provided for `%s` must have unique items, but the following items had multiple entries: "
+                    + "[`%s`]", shape.getId(), String.join("`, `", duplicateValues)));
+        }
+    }
+}

smithy-model/src/test/java/software/amazon/smithy/model/validation/NodeValidationVisitorTest.java

@@ -207,6 +207,13 @@ public static Collection<Object[]> data() {
                 {"ns.foo#List", "[10]", new String[] {"0: Expected string value for string shape, `ns.foo#String`; found number value, `10`"}},
                 {"ns.foo#List", "10", new String[] {"Expected array value for list shape, `ns.foo#List`; found number value, `10`"}},
 
+                // unique list
+                {"ns.foo#UniqueList", "[\"a\"]", null},
+                {"ns.foo#UniqueList", "[\"a\", \"b\"]", null},
+                {"ns.foo#UniqueList", "[\"a\", \"a\"]", new String[] {"Value provided for `ns.foo#UniqueList` must have unique items, but the following items had multiple entries: [`a`]"}},
+                {"ns.foo#UniqueList", "[\"a\", \"a\", \"a\"]", new String[] {"Value provided for `ns.foo#UniqueList` must have unique items, but the following items had multiple entries: [`a`]"}},
+                {"ns.foo#UniqueList", "[\"a\", \"a\", \"b\", \"b\"]", new String[] {"Value provided for `ns.foo#UniqueList` must have unique items, but the following items had multiple entries: [`a`, `b`]"}},
+
                 // map
                 {"ns.foo#Map", "{\"a\":[\"b\"]}", null},
                 {"ns.foo#Map", "{\"a\":[\"b\"], \"c\":[\"d\"]}", null},

smithy-model/src/test/resources/software/amazon/smithy/model/validation/node-validator.json

@@ -133,6 +133,15 @@
                 }
             }
         },
+        "ns.foo#UniqueList": {
+            "type": "list",
+            "member": {
+                "target": "ns.foo#String"
+            },
+            "traits": {
+                "smithy.api#uniqueItems": {}
+            }
+        },
         "ns.foo#String": {
             "type": "string"
         },