Add uniqueItems trait information

Author: JordonPhillips

smithy-docgen-core/src/main/java/software/amazon/smithy/docgen/core/integrations/BuiltinsIntegration.java

@@ -24,6 +24,7 @@
 import software.amazon.smithy.docgen.core.interceptors.RecommendedInterceptor;
 import software.amazon.smithy.docgen.core.interceptors.SensitiveInterceptor;
 import software.amazon.smithy.docgen.core.interceptors.SinceInterceptor;
+import software.amazon.smithy.docgen.core.interceptors.UniqueItemsInterceptor;
 import software.amazon.smithy.docgen.core.interceptors.UnstableInterceptor;
 import software.amazon.smithy.docgen.core.writers.DocWriter;
 import software.amazon.smithy.docgen.core.writers.MarkdownWriter;
@@ -68,6 +69,7 @@ public List<? extends CodeInterceptor<? extends CodeSection, DocWriter>> interce
         return List.of(
                 new NoReplaceBindingInterceptor(),
                 new NoReplaceOperationInterceptor(),
+                new UniqueItemsInterceptor(),
                 new PatternInterceptor(),
                 new RangeInterceptor(),
                 new LengthInterceptor(),

smithy-docgen-core/src/main/java/software/amazon/smithy/docgen/core/interceptors/UniqueItemsInterceptor.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package software.amazon.smithy.docgen.core.interceptors;
+
+import software.amazon.smithy.docgen.core.sections.ShapeSubheadingSection;
+import software.amazon.smithy.docgen.core.writers.DocWriter;
+import software.amazon.smithy.model.traits.UniqueItemsTrait;
+import software.amazon.smithy.utils.CodeInterceptor;
+import software.amazon.smithy.utils.SmithyInternalApi;
+
+/**
+ * Adds an annotation to docs for lists with the
+ * <a href="https://smithy.io/2.0/spec/constraint-traits.html#uniqueitems-trait">
+ * uniqueItems trait</a>.
+ */
+@SmithyInternalApi
+public final class UniqueItemsInterceptor implements CodeInterceptor<ShapeSubheadingSection, DocWriter> {
+    @Override
+    public Class<ShapeSubheadingSection> sectionType() {
+        return ShapeSubheadingSection.class;
+    }
+
+    @Override
+    public boolean isIntercepted(ShapeSubheadingSection section) {
+        return section.shape().getMemberTrait(section.context().model(), UniqueItemsTrait.class).isPresent();
+    }
+
+    @Override
+    public void write(DocWriter writer, String previousText, ShapeSubheadingSection section) {
+        writer.write("""
+                Items in this list MUST be unique.
+
+                $L""", previousText);
+    }
+}

smithy-docgen-test/model/main.smithy

@@ -122,12 +122,14 @@ structure LengthTraitExamples {
     blob: Blob
 
     @length(min: 2, max: 4)
-    list: StringList
+    list: StringSet
 
     map: StringMap
 }
 
-list StringList {
+/// A set of strings.
+@uniqueItems
+list StringSet {
     member: String
 }