Add httpHeader trait support

Author: JordonPhillips

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

@@ -15,6 +15,7 @@
 import software.amazon.smithy.docgen.core.interceptors.DeprecatedInterceptor;
 import software.amazon.smithy.docgen.core.interceptors.ErrorFaultInterceptor;
 import software.amazon.smithy.docgen.core.interceptors.ExternalDocsInterceptor;
+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.HttpPrefixHeadersInterceptor;
@@ -92,6 +93,7 @@ public List<? extends CodeInterceptor<? extends CodeSection, DocWriter>> interce
                 new XmlAttributeInterceptor(),
                 new XmlNameInterceptor(),
                 new XmlFlattenedInterceptor(),
+                new HttpHeaderInterceptor(),
                 new HttpPrefixHeadersInterceptor(),
                 new HttpQueryParamsInterceptor(),
                 new HttpQueryInterceptor(),

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

@@ -0,0 +1,44 @@
+/*
+ * 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.HttpHeaderTrait;
+import software.amazon.smithy.utils.SmithyInternalApi;
+
+/**
+ * Adds information about header bindings from the
+ * <a href="https://smithy.io/2.0/spec/http-bindings.html#httpheader-trait">
+ * httpHeader trait</a> if the protocol supports it.
+ */
+@SmithyInternalApi
+public final class HttpHeaderInterceptor extends ProtocolTraitInterceptor<HttpHeaderTrait> {
+    @Override
+    protected Class<HttpHeaderTrait> getTraitClass() {
+        return HttpHeaderTrait.class;
+    }
+
+    @Override
+    protected ShapeId getTraitId() {
+        return HttpHeaderTrait.ID;
+    }
+
+    @Override
+    void write(DocWriter writer, String previousText, ProtocolSection section, HttpHeaderTrait trait) {
+        var target = section.context().model().expectShape(section.shape().asMemberShape().get().getTarget());
+        writer.putContext("key", trait.getValue());
+        writer.putContext("list", target.isListShape());
+        writer.write("""
+                This is bound to the HTTP header ${param:`}.${?list} Each element in \
+                the list should be sent as its own header using the same key for each \
+                value. The list may instead be concatenated with commas separating each \
+                value.${/list}
+
+                $L""", previousText);
+    }
+}