Allow specifying xml namespace prefix

docs/source/spec/xml.rst

@@ -221,8 +221,9 @@ following document:
     ``-``. Values for an ``xmlName`` adhere to the following ABNF.
 
 .. productionlist:: smithy
-    xml_name       :(ALPHA / "_")
+    xml_identifier :(ALPHA / "_")
                    :*(ALPHA / DIGIT / "-" / "_")
+    xml_name       :xml_identifier / (xml_identifier ":" xml_identifier)
 
 
 .. _xmlNamespace-trait:
@@ -252,6 +253,9 @@ The ``xmlNamespace`` trait is an object that contains the following properties:
     * - uri
       - ``string`` value containing a valid URI
       - **Required**. The namespace URI for scoping this XML element.
+    * - prefix
+      - ``string`` value
+      - The prefix for elements from this namespace.
 
 Given the following structure definition,
 
@@ -306,6 +310,71 @@ following document:
         <bar>def</bar>
     </MyStructure>
 
+Given the following definition with a prefix:
+
+.. tabs::
+
+    .. code-tab:: smithy
+
+        @xmlNamespace(uri: "http://foo.com", prefix: "bar")
+        structure MyStructure {
+            foo: String,
+            @xmlName("baz:bar")
+            bar: String,
+        }
+
+    .. code-tab:: json
+
+        {
+            "smithy": "0.4.0",
+            "smithy.example": {
+                "shapes": {
+                    "MyStructure": {
+                        "type": "structure",
+                        "members": {
+                            "foo": {
+                                "target": "String"
+                            },
+                            "bar": {
+                                "target": "String",
+                                "xmlName": "baz:bar"
+                            }
+                        },
+                        "xmlNamespace": {
+                            "uri": "http://foo.com",
+                            "prefix": "baz"
+                        }
+                    }
+                }
+            }
+        }
+
+and the following values provided for ``MyStructure``,
+
+::
+
+    "foo" = "abc"
+    "bar" = "def"
+
+the XML representation of the value would be serialized with the
+following document:
+
+.. code-block:: xml
+
+    <MyStructure xmlns:baz="http//foo.com">
+        <foo>abc</foo>
+        <baz:bar>def</baz:bar>
+    </MyStructure>
+
+.. note::
+
+    Values for the ``prefix`` option must start with a letter (lower/upper
+    case) or ``_``, followed by letters (lower/upper case), digits, ``_``, or
+    ``-``. Values for ``prefix`` adhere to the following ABNF.
+
+.. productionlist:: smithy
+    xml_prefix      :(ALPHA / "_")
+                    :*(ALPHA / DIGIT / "-" / "_")
 
 .. _xml-examples:
 

smithy-model/src/main/java/software/amazon/smithy/model/traits/XmlNamespaceTrait.java

@@ -17,8 +17,10 @@
 
 import java.util.List;
 import java.util.Objects;
+import java.util.Optional;
 import software.amazon.smithy.model.node.Node;
 import software.amazon.smithy.model.node.ObjectNode;
+import software.amazon.smithy.model.node.StringNode;
 import software.amazon.smithy.model.shapes.ShapeId;
 import software.amazon.smithy.utils.ListUtils;
 import software.amazon.smithy.utils.MapUtils;
@@ -31,23 +33,32 @@
 public final class XmlNamespaceTrait extends AbstractTrait implements ToSmithyBuilder<XmlNamespaceTrait> {
     public static final ShapeId ID = ShapeId.from("smithy.api#xmlNamespace");
 
-    private static final List<String> XML_NAMESPACE_PROPERTIES = ListUtils.of("uri");
+    private static final String PREFIX = "prefix";
+    private static final String URI = "uri";
+    private static final List<String> XML_NAMESPACE_PROPERTIES = ListUtils.of(URI, PREFIX);
 
+    private final String prefix;
     private final String uri;
 
     private XmlNamespaceTrait(Builder builder) {
         super(ID, builder.getSourceLocation());
         uri = SmithyBuilder.requiredState("uri", builder.uri);
+        prefix = builder.prefix;
     }
 
     public String getUri() {
         return uri;
     }
 
+    public Optional<String> getPrefix() {
+        return Optional.ofNullable(prefix);
+    }
+
     @Override
     protected Node createNode() {
         return new ObjectNode(MapUtils.of(), getSourceLocation())
-                .withMember("uri", Node.from(uri));
+                .withMember(URI, Node.from(uri))
+                .withOptionalMember(PREFIX, getPrefix().map(Node::from));
     }
 
     /**
@@ -59,14 +70,18 @@ public static Builder builder() {
 
     @Override
     public Builder toBuilder() {
-        return builder().sourceLocation(getSourceLocation()).uri(uri);
+        return builder()
+                .sourceLocation(getSourceLocation())
+                .uri(uri)
+                .prefix(prefix);
     }
 
     /**
     * Builder used to create an XmlNamespace trait.
     */
     public static final class Builder extends AbstractTraitBuilder<XmlNamespaceTrait, Builder> {
         private String uri;
+        private String prefix;
 
         private Builder() {}
 
@@ -75,6 +90,11 @@ public Builder uri(String uri) {
             return this;
         }
 
+        public Builder prefix(String prefix) {
+            this.prefix = prefix;
+            return this;
+        }
+
         @Override
         public XmlNamespaceTrait build() {
             return new XmlNamespaceTrait(this);
@@ -92,7 +112,8 @@ public XmlNamespaceTrait createTrait(ShapeId target, Node value) {
             Builder builder = builder().sourceLocation(value);
             ObjectNode node = value.expectObjectNode();
             node.warnIfAdditionalProperties(XML_NAMESPACE_PROPERTIES);
-            builder.uri(node.expectStringMember("uri").getValue());
+            builder.uri(node.expectStringMember(URI).getValue());
+            node.getStringMember(PREFIX).map(StringNode::getValue).ifPresent(builder::prefix);
             return builder.build();
         }
     }

smithy-model/src/main/resources/software/amazon/smithy/model/loader/prelude-traits.smithy

@@ -156,7 +156,7 @@ structure xmlFlattened {}
 /// used in the model.
 @trait
 @tags(["diff.error.const"])
-@pattern("^[a-zA-Z_][a-zA-Z_0-9-]*$")
+@pattern("^[a-zA-Z_][a-zA-Z_0-9-]*(:[a-zA-Z_][a-zA-Z_0-9-]*)?$")
 string xmlName
 
 /// Adds an xmlns namespace definition URI to an XML element.
@@ -166,6 +166,9 @@ structure xmlNamespace {
     /// The namespace URI for scoping this XML element.
     @required
     uri: NonEmptyString,
+    /// The prefix for the given namespace.
+    @pattern("^[a-zA-Z_][a-zA-Z_0-9-]*$")
+    prefix: NonEmptyString,
 }
 
 @private

smithy-model/src/test/java/software/amazon/smithy/model/traits/XmlNameTraitTest.java

@@ -38,4 +38,17 @@ public void loadsTraitWithString() {
         assertThat(xmlNameTrait.getValue(), equalTo("Text"));
         assertThat(xmlNameTrait.toNode(), equalTo(node));
     }
+
+    @Test
+    public void loadsWithColonInValue() {
+        Node node = Node.from("xsi:type");
+        TraitFactory provider = TraitFactory.createServiceFactory();
+        Optional<Trait> trait = provider.createTrait(ShapeId.from("smithy.api#xmlName"), ShapeId.from("ns.qux#foo"), node);
+
+        assertTrue(trait.isPresent());
+        assertThat(trait.get(), instanceOf(XmlNameTrait.class));
+        XmlNameTrait xmlNameTrait = (XmlNameTrait) trait.get();
+        assertThat(xmlNameTrait.getValue(), equalTo("xsi:type"));
+        assertThat(xmlNameTrait.toNode(), equalTo(node));
+    }
 }

smithy-model/src/test/java/software/amazon/smithy/model/traits/XmlNamespaceTraitTest.java

@@ -55,4 +55,21 @@ public void omitsEmptiesFromSerializedNode() {
 
         assertFalse(serialized.getMember("prefix").isPresent());
     }
+
+    @Test
+    public void loadsTraitWithPrefix() {
+        TraitFactory provider = TraitFactory.createServiceFactory();
+        ObjectNode node = Node.objectNode()
+                .withMember("uri", Node.from("https://www.amazon.com"))
+                .withMember("prefix", Node.from("xsi"));
+        Optional<Trait> trait = provider.createTrait(
+                ShapeId.from("smithy.api#xmlNamespace"), ShapeId.from("ns.qux#foo"), node);
+        assertTrue(trait.isPresent());
+        assertThat(trait.get(), instanceOf(XmlNamespaceTrait.class));
+        XmlNamespaceTrait xmlNamespace = (XmlNamespaceTrait) trait.get();
+
+        assertThat(xmlNamespace.getUri(), equalTo("https://www.amazon.com"));
+        assertTrue(xmlNamespace.getPrefix().isPresent());
+        assertThat(xmlNamespace.getPrefix().get(), equalTo("xsi"));
+    }
 }

smithy-model/src/test/resources/software/amazon/smithy/model/errorfiles/validators/xml-name.errors

@@ -0,0 +1 @@
+[ERROR] ns.foo#InvalidName$a: Error validating trait `xmlName`: String value provided for `smithy.api#xmlName` must match regular expression: ^[a-zA-Z_][a-zA-Z_0-9-]*(:[a-zA-Z_][a-zA-Z_0-9-]*)?$ | TraitValue

smithy-model/src/test/resources/software/amazon/smithy/model/errorfiles/validators/xml-name.json

@@ -0,0 +1,34 @@
+{
+    "smithy": "0.4.0",
+    "ns.foo": {
+        "shapes": {
+            "ValidName1": {
+                "type": "structure",
+                "members": {
+                    "a": {
+                        "target": "smithy.api#String",
+                        "smithy.api#xmlName": "customname"
+                    }
+                }
+            },
+            "ValidName2": {
+                "type": "structure",
+                "members": {
+                    "a": {
+                        "target": "smithy.api#String",
+                        "smithy.api#xmlName": "customprefix:customname"
+                    }
+                }
+            },
+            "InvalidName": {
+                "type": "structure",
+                "members": {
+                    "a": {
+                        "target": "smithy.api#String",
+                        "smithy.api#xmlName": "too:many:colons"
+                    }
+                }
+            }
+        }
+    }
+}

smithy-model/src/test/resources/software/amazon/smithy/model/errorfiles/validators/xml-namespace.json

@@ -13,6 +13,18 @@
           "uri": "http://foo.com"
         }
       },
+      "ValidNamespace2": {
+        "type": "structure",
+        "members": {
+          "a": {
+            "target": "String"
+          }
+        },
+        "smithy.api#xmlNamespace": {
+          "uri": "http://www.w3.org/2001/XMLSchema-instance",
+          "prefix": "xsi"
+        }
+      },
       "InvalidNamespace": {
         "type": "structure",
         "members": {