Add httpPayload trait support

Author: JordonPhillips

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

@@ -19,6 +19,7 @@
 import software.amazon.smithy.docgen.core.interceptors.HttpHeaderInterceptor;
 import software.amazon.smithy.docgen.core.interceptors.HttpInterceptor;
 import software.amazon.smithy.docgen.core.interceptors.HttpLabelInterceptor;
+import software.amazon.smithy.docgen.core.interceptors.HttpPayloadInterceptor;
 import software.amazon.smithy.docgen.core.interceptors.HttpPrefixHeadersInterceptor;
 import software.amazon.smithy.docgen.core.interceptors.HttpQueryInterceptor;
 import software.amazon.smithy.docgen.core.interceptors.HttpQueryParamsInterceptor;
@@ -94,6 +95,7 @@ public List<? extends CodeInterceptor<? extends CodeSection, DocWriter>> interce
                 new XmlAttributeInterceptor(),
                 new XmlNameInterceptor(),
                 new XmlFlattenedInterceptor(),
+                new HttpPayloadInterceptor(),
                 new HttpErrorInterceptor(),
                 new HttpHeaderInterceptor(),
                 new HttpPrefixHeadersInterceptor(),

smithy-docgen-core/src/main/java/software/amazon/smithy/docgen/core/interceptors/HttpPayloadInterceptor.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.ProtocolSection;
+import software.amazon.smithy.docgen.core.writers.DocWriter;
+import software.amazon.smithy.model.shapes.ShapeId;
+import software.amazon.smithy.model.traits.HttpPayloadTrait;
+import software.amazon.smithy.utils.SmithyInternalApi;
+
+/**
+ * Adds information about payload bindings from the
+ * <a href="https://smithy.io/2.0/spec/http-bindings.html#httppayload-trait">
+ * httpPayload trait</a> if the protocol supports it.
+ */
+@SmithyInternalApi
+public final class HttpPayloadInterceptor extends ProtocolTraitInterceptor<HttpPayloadTrait> {
+    @Override
+    protected Class<HttpPayloadTrait> getTraitClass() {
+        return HttpPayloadTrait.class;
+    }
+
+    @Override
+    protected ShapeId getTraitId() {
+        return HttpPayloadTrait.ID;
+    }
+
+    @Override
+    void write(DocWriter writer, String previousText, ProtocolSection section, HttpPayloadTrait trait) {
+        writer.write("""
+                This is bound directly to the HTTP message body without wrapping.
+
+                $L""", previousText);
+    }
+}