Add support for json schema oneOf enumStrategy (#2504)

This adds support for a new json schema setting, `enumStrategy`, that allows for variants
`enum` (current behaviour, and default) and `oneOf` (gets converted to a oneOf with const
string values, allowing for documentation of individual enum variants.)

Author: nated0g

smithy-jsonschema/src/main/java/software/amazon/smithy/jsonschema/JsonSchemaConfig.java

@@ -85,11 +85,42 @@ public String toString() {
         }
     }
 
+    /**
+     * Configures how Smithy enum shapes are converted to JSON Schema
+     */
+    public enum EnumStrategy {
+
+        /**
+         * Converts to a schema that uses enum, which contains an array of strings
+         *
+         * <p>This is the default setting used if not configured.
+         */
+        ENUM("enum"),
+
+        /**
+         * Converts to a schema that uses oneOf, with an array of const strings and optional
+         * descriptions for documentation purposes
+         */
+        ONE_OF("oneOf");
+
+        private final String stringValue;
+
+        EnumStrategy(String stringValue) {
+            this.stringValue = stringValue;
+        }
+
+        @Override
+        public String toString() {
+            return stringValue;
+        }
+    }
+
     private boolean alphanumericOnlyRefs;
     private boolean useJsonName;
     private TimestampFormatTrait.Format defaultTimestampFormat = TimestampFormatTrait.Format.DATE_TIME;
     private UnionStrategy unionStrategy = UnionStrategy.ONE_OF;
     private MapStrategy mapStrategy = MapStrategy.PROPERTY_NAMES;
+    private EnumStrategy enumStrategy = EnumStrategy.ENUM;
     private String definitionPointer;
     private ObjectNode schemaDocumentExtensions = Node.objectNode();
     private ObjectNode extensions = Node.objectNode();
@@ -186,6 +217,18 @@ public void setMapStrategy(MapStrategy mapStrategy) {
         this.mapStrategy = mapStrategy;
     }
 
+    public EnumStrategy getEnumStrategy() {
+        return enumStrategy;
+    }
+
+    /**
+     * Configures how Smithy enum shapes ae converted to JSON Schema
+     * @param enumStrategy The enum strategy to use
+     */
+    public void setEnumStrategy(EnumStrategy enumStrategy) {
+        this.enumStrategy = enumStrategy;
+    }
+
     public String getDefinitionPointer() {
         return definitionPointer != null ? definitionPointer : jsonSchemaVersion.getDefaultDefinitionPointer();
     }

smithy-jsonschema/src/main/java/software/amazon/smithy/jsonschema/JsonSchemaShapeVisitor.java

@@ -7,18 +7,21 @@
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
+import java.util.Map;
 import java.util.Optional;
 import java.util.Set;
 import java.util.regex.Pattern;
 import software.amazon.smithy.model.Model;
 import software.amazon.smithy.model.node.Node.NonNumericFloat;
+import software.amazon.smithy.model.node.StringNode;
 import software.amazon.smithy.model.shapes.BigDecimalShape;
 import software.amazon.smithy.model.shapes.BigIntegerShape;
 import software.amazon.smithy.model.shapes.BlobShape;
 import software.amazon.smithy.model.shapes.BooleanShape;
 import software.amazon.smithy.model.shapes.ByteShape;
 import software.amazon.smithy.model.shapes.DocumentShape;
 import software.amazon.smithy.model.shapes.DoubleShape;
+import software.amazon.smithy.model.shapes.EnumShape;
 import software.amazon.smithy.model.shapes.FloatShape;
 import software.amazon.smithy.model.shapes.IntegerShape;
 import software.amazon.smithy.model.shapes.ListShape;
@@ -248,6 +251,43 @@ public Schema unionShape(UnionShape shape) {
         }
     }
 
+    @Override
+    public Schema enumShape(EnumShape shape) {
+        JsonSchemaConfig.EnumStrategy enumStrategy = converter.getConfig().getEnumStrategy();
+
+        switch (enumStrategy) {
+            case ENUM:
+                return super.enumShape(shape);
+            case ONE_OF:
+                Map<String, String> enumValues = shape.getEnumValues();
+                List<Schema> schemas = new ArrayList<>();
+
+                for (Map.Entry<String, MemberShape> entry : shape.getAllMembers().entrySet()) {
+                    String memberName = entry.getKey();
+                    MemberShape member = entry.getValue();
+                    Schema enumSchema = Schema.builder()
+                            .constValue(StringNode.from(enumValues.get(memberName)))
+                            .description(member.getTrait(DocumentationTrait.class)
+                                    .map(DocumentationTrait::getValue)
+                                    .orElse(null))
+                            .build();
+
+                    schemas.add(enumSchema);
+                }
+
+                return buildSchema(shape,
+                        Schema.builder()
+                                .description(shape.getTrait(DocumentationTrait.class)
+                                        .map(DocumentationTrait::getValue)
+                                        .orElse(null))
+                                .type("string")
+                                .oneOf(schemas));
+            default: {
+                throw new SmithyJsonSchemaException(String.format("Unsupported enum strategy: %s", enumStrategy));
+            }
+        }
+    }
+
     @Override
     public Schema timestampShape(TimestampShape shape) {
         return buildSchema(shape, createBuilder(shape, "string"));

smithy-jsonschema/src/test/java/software/amazon/smithy/jsonschema/JsonSchemaConverterTest.java

@@ -817,6 +817,43 @@ public void supportsIntEnumsByDefault() {
         Node.assertEquals(document.toNode(), expected);
     }
 
+    @Test
+    public void supportsDefaultEnumStrategy() {
+        Model model = Model.assembler()
+                .addImport(getClass().getResource("string-enums.smithy"))
+                .assemble()
+                .unwrap();
+
+        SchemaDocument document = JsonSchemaConverter.builder()
+                .model(model)
+                .build()
+                .convert();
+
+        Node expected = Node.parse(
+                IoUtils.toUtf8String(getClass().getResourceAsStream("string-enums.jsonschema.v07.json")));
+        Node.assertEquals(document.toNode(), expected);
+    }
+
+    @Test
+    public void supportsOneOfEnumStrategy() {
+        Model model = Model.assembler()
+                .addImport(getClass().getResource("string-enums.smithy"))
+                .assemble()
+                .unwrap();
+
+        JsonSchemaConfig config = new JsonSchemaConfig();
+        config.setEnumStrategy(JsonSchemaConfig.EnumStrategy.ONE_OF);
+        SchemaDocument document = JsonSchemaConverter.builder()
+                .model(model)
+                .config(config)
+                .build()
+                .convert();
+
+        Node expected = Node.parse(
+                IoUtils.toUtf8String(getClass().getResourceAsStream("string-enums-one-of.jsonschema.v07.json")));
+        Node.assertEquals(document.toNode(), expected);
+    }
+
     @Test
     public void intEnumsCanBeDisabled() {
         Model model = Model.assembler()

smithy-jsonschema/src/test/resources/software/amazon/smithy/jsonschema/string-enums-one-of.jsonschema.v07.json

@@ -0,0 +1,25 @@
+{
+  "definitions": {
+    "Foo": {
+      "type": "object",
+      "properties": {
+        "bar": {
+          "$ref": "#/definitions/TestEnum"
+        }
+      }
+    },
+    "TestEnum": {
+      "type": "string",
+      "description": "This is a test enum",
+      "oneOf": [
+        {
+          "const": "Foo",
+          "description": "it really does foo"
+        },
+        {
+          "const": "Bar"
+        }
+      ]
+    }
+  }
+}

smithy-jsonschema/src/test/resources/software/amazon/smithy/jsonschema/string-enums.jsonschema.v07.json

@@ -0,0 +1,20 @@
+{
+    "definitions": {
+        "Foo": {
+            "type": "object",
+            "properties": {
+                "bar": {
+                    "$ref": "#/definitions/TestEnum"
+                }
+            }
+        },
+        "TestEnum": {
+            "type": "string",
+            "enum": [
+                "Foo",
+                "Bar"
+            ],
+            "description": "This is a test enum"
+        }
+    }
+}

smithy-jsonschema/src/test/resources/software/amazon/smithy/jsonschema/string-enums.smithy

@@ -0,0 +1,14 @@
+$version: "2.0"
+
+namespace smithy.example
+
+structure Foo {
+    bar: TestEnum
+}
+
+@documentation("This is a test enum")
+enum TestEnum {
+    @documentation("it really does foo")
+    FOO = "Foo"
+    BAR = "Bar"
+}