feat: support Smithy default trait (#857)

.changes/d3ec877c-68c6-4c21-881f-8767d1f87e1c.json

@@ -0,0 +1,8 @@
+{
+    "id": "d3ec877c-68c6-4c21-881f-8767d1f87e1c",
+    "type": "feature",
+    "description": "Support Smithy default trait",
+    "issues": [
+        "https://github.com/awslabs/smithy-kotlin/issues/718"
+    ]
+}

codegen/smithy-kotlin-codegen-testutils/src/main/kotlin/software/amazon/smithy/kotlin/codegen/test/ModelTestUtils.kt

@@ -28,14 +28,14 @@ import java.net.URL
 
 /**
  * Unless necessary to deviate for test reasons, the following literals should be used in test models:
- *  smithy version: "1"
- *  model version: "1.0.0"
+ *  smithy version: "2"
+ *  model version: "2.0.0"
  *  namespace: TestDefault.NAMESPACE
  *  service name: "Test"
  */
 object TestModelDefault {
-    const val SMITHY_IDL_VERSION = "1"
-    const val MODEL_VERSION = "1.0.0"
+    const val SMITHY_IDL_VERSION = "2"
+    const val MODEL_VERSION = "2.0.0"
     const val NAMESPACE = "com.test"
     const val SERVICE_NAME = "Test"
     const val SDK_ID = "Test"

codegen/smithy-kotlin-codegen/src/main/kotlin/software/amazon/smithy/kotlin/codegen/core/KotlinSymbolProvider.kt

@@ -8,9 +8,11 @@ import software.amazon.smithy.codegen.core.*
 import software.amazon.smithy.kotlin.codegen.KotlinSettings
 import software.amazon.smithy.kotlin.codegen.lang.kotlinReservedWords
 import software.amazon.smithy.kotlin.codegen.model.*
+import software.amazon.smithy.kotlin.codegen.utils.dq
 import software.amazon.smithy.model.Model
 import software.amazon.smithy.model.knowledge.NullableIndex
 import software.amazon.smithy.model.shapes.*
+import software.amazon.smithy.model.traits.DefaultTrait
 import software.amazon.smithy.model.traits.SparseTrait
 import software.amazon.smithy.model.traits.StreamingTrait
 import java.util.logging.Logger
@@ -75,31 +77,29 @@ class KotlinSymbolProvider(private val model: Model, private val settings: Kotli
 
     override fun longShape(shape: LongShape): Symbol = numberShape(shape, "Long", "0L")
 
-    override fun floatShape(shape: FloatShape): Symbol = numberShape(shape, "Float", "0.0f")
+    override fun floatShape(shape: FloatShape): Symbol = numberShape(shape, "Float", "0f")
 
     override fun doubleShape(shape: DoubleShape): Symbol = numberShape(shape, "Double", "0.0")
 
     private fun numberShape(shape: Shape, typeName: String, defaultValue: String = "0"): Symbol =
-        createSymbolBuilder(shape, typeName, namespace = "kotlin")
-            .defaultValue(defaultValue)
-            .build()
+        createSymbolBuilder(shape, typeName, namespace = "kotlin").defaultValue(defaultValue).build()
 
     override fun bigIntegerShape(shape: BigIntegerShape?): Symbol = createBigSymbol(shape, "BigInteger")
 
     override fun bigDecimalShape(shape: BigDecimalShape?): Symbol = createBigSymbol(shape, "BigDecimal")
 
     private fun createBigSymbol(shape: Shape?, symbolName: String): Symbol =
-        createSymbolBuilder(shape, symbolName, namespace = "java.math", boxed = true).build()
+        createSymbolBuilder(shape, symbolName, namespace = "java.math", nullable = true).build()
 
     override fun stringShape(shape: StringShape): Symbol = if (shape.isEnum) {
         createEnumSymbol(shape)
     } else {
-        createSymbolBuilder(shape, "String", boxed = true, namespace = "kotlin").build()
+        createSymbolBuilder(shape, "String", nullable = true, namespace = "kotlin").build()
     }
 
     private fun createEnumSymbol(shape: Shape): Symbol {
         val namespace = "$rootNamespace.model"
-        return createSymbolBuilder(shape, shape.defaultName(service), namespace, boxed = true)
+        return createSymbolBuilder(shape, shape.defaultName(service), namespace, nullable = true)
             .definitionFile("${shape.defaultName(service)}.kt")
             .build()
     }
@@ -110,7 +110,7 @@ class KotlinSymbolProvider(private val model: Model, private val settings: Kotli
     override fun structureShape(shape: StructureShape): Symbol {
         val name = shape.defaultName(service)
         val namespace = "$rootNamespace.model"
-        val builder = createSymbolBuilder(shape, name, namespace, boxed = true)
+        val builder = createSymbolBuilder(shape, name, namespace, nullable = true)
             .definitionFile("$name.kt")
 
         // add a reference to each member symbol
@@ -149,7 +149,7 @@ class KotlinSymbolProvider(private val model: Model, private val settings: Kotli
     override fun listShape(shape: ListShape): Symbol {
         val reference = toSymbol(shape.member)
         val valueType = if (shape.hasTrait<SparseTrait>()) "${reference.name}?" else reference.name
-        return createSymbolBuilder(shape, "List<$valueType>", boxed = true)
+        return createSymbolBuilder(shape, "List<$valueType>", nullable = true)
             .addReferences(reference)
             .putProperty(SymbolProperty.MUTABLE_COLLECTION_FUNCTION, "mutableListOf<$valueType>")
             .putProperty(SymbolProperty.IMMUTABLE_COLLECTION_FUNCTION, "listOf<$valueType>")
@@ -160,7 +160,7 @@ class KotlinSymbolProvider(private val model: Model, private val settings: Kotli
         val reference = toSymbol(shape.value)
         val valueType = if (shape.hasTrait<SparseTrait>()) "${reference.name}?" else reference.name
 
-        return createSymbolBuilder(shape, "Map<String, $valueType>", boxed = true)
+        return createSymbolBuilder(shape, "Map<String, $valueType>", nullable = true)
             .addReferences(reference)
             .putProperty(SymbolProperty.MUTABLE_COLLECTION_FUNCTION, "mutableMapOf<String, $valueType>")
             .putProperty(SymbolProperty.IMMUTABLE_COLLECTION_FUNCTION, "mapOf<String, $valueType>")
@@ -172,11 +172,17 @@ class KotlinSymbolProvider(private val model: Model, private val settings: Kotli
         val targetShape =
             model.getShape(shape.target).orElseThrow { CodegenException("Shape not found: ${shape.target}") }
 
-        val targetSymbol = if (nullableIndex.isMemberNullable(shape, NullableIndex.CheckMode.CLIENT_ZERO_VALUE_V1_NO_INPUT)) {
-            toSymbol(targetShape).toBuilder().boxed().build()
-        } else {
-            toSymbol(targetShape)
-        }
+        val targetSymbol = toSymbol(targetShape)
+            .toBuilder()
+            .apply {
+                if (nullableIndex.isMemberNullable(shape, NullableIndex.CheckMode.CLIENT_ZERO_VALUE_V1_NO_INPUT)) nullable()
+
+                shape.getTrait<DefaultTrait>()?.let {
+                    defaultValue(it.getDefaultValue(targetShape), DefaultValueType.MODELED)
+                }
+            }
+            .build()
+
         // figure out if we are referencing an event stream or not.
         // NOTE: unlike blob streams we actually re-use the target (union) shape which is why we can't do this
         // when visiting a unionShape() like we can for blobShape()
@@ -197,9 +203,18 @@ class KotlinSymbolProvider(private val model: Model, private val settings: Kotli
         }
     }
 
+    private fun DefaultTrait.getDefaultValue(targetShape: Shape): String? = when {
+        toNode().toString() == "null" || targetShape is BlobShape && toNode().toString() == "" -> null
+        toNode().isNumberNode -> getDefaultValueForNumber(targetShape, toNode().toString())
+        toNode().isArrayNode -> "listOf()"
+        toNode().isObjectNode -> "mapOf()"
+        toNode().isStringNode -> toNode().toString().dq()
+        else -> toNode().toString()
+    }
+
     override fun timestampShape(shape: TimestampShape?): Symbol {
         val dependency = KotlinDependency.CORE
-        return createSymbolBuilder(shape, "Instant", boxed = true)
+        return createSymbolBuilder(shape, "Instant", nullable = true)
             .namespace("${dependency.namespace}.time", ".")
             .addDependency(dependency)
             .build()
@@ -208,7 +223,7 @@ class KotlinSymbolProvider(private val model: Model, private val settings: Kotli
     override fun blobShape(shape: BlobShape): Symbol = if (shape.hasTrait<StreamingTrait>()) {
         RuntimeTypes.Core.Content.ByteStream.asNullable()
     } else {
-        createSymbolBuilder(shape, "ByteArray", boxed = true, namespace = "kotlin").build()
+        createSymbolBuilder(shape, "ByteArray", nullable = true, namespace = "kotlin").build()
     }
 
     override fun documentShape(shape: DocumentShape?): Symbol =
@@ -217,7 +232,7 @@ class KotlinSymbolProvider(private val model: Model, private val settings: Kotli
     override fun unionShape(shape: UnionShape): Symbol {
         val name = shape.defaultName(service)
         val namespace = "$rootNamespace.model"
-        val builder = createSymbolBuilder(shape, name, namespace, boxed = true)
+        val builder = createSymbolBuilder(shape, name, namespace, nullable = true)
             .definitionFile("$name.kt")
 
         // add a reference to each member symbol
@@ -243,16 +258,23 @@ class KotlinSymbolProvider(private val model: Model, private val settings: Kotli
     /**
      * Creates a symbol builder for the shape with the given type name in the root namespace.
      */
-    private fun createSymbolBuilder(shape: Shape?, typeName: String, boxed: Boolean = false): Symbol.Builder {
+    private fun createSymbolBuilder(shape: Shape?, typeName: String, nullable: Boolean = false): Symbol.Builder {
         val builder = Symbol.builder()
             .putProperty(SymbolProperty.SHAPE_KEY, shape)
             .name(typeName)
-        if (boxed) {
-            builder.boxed()
+        if (nullable) {
+            builder.nullable()
         }
         return builder
     }
 
+    private fun getDefaultValueForNumber(shape: Shape, value: String) = when (shape) {
+        is LongShape -> "${value}L"
+        is FloatShape -> "${value}f"
+        is DoubleShape -> if (value.matches("[0-9]*\\.[0-9]+".toRegex())) value else "$value.0"
+        else -> value
+    }
+
     /**
      * Creates a symbol builder for the shape with the given type name in a child namespace relative
      * to the root namespace e.g. `relativeNamespace = bar` with a root namespace of `foo` would set
@@ -262,8 +284,8 @@ class KotlinSymbolProvider(private val model: Model, private val settings: Kotli
         shape: Shape?,
         typeName: String,
         namespace: String,
-        boxed: Boolean = false,
-    ): Symbol.Builder = createSymbolBuilder(shape, typeName, boxed).namespace(namespace, ".")
+        nullable: Boolean = false,
+    ): Symbol.Builder = createSymbolBuilder(shape, typeName, nullable).namespace(namespace, ".")
 }
 
 // Add a reference and it's children

codegen/smithy-kotlin-codegen/src/main/kotlin/software/amazon/smithy/kotlin/codegen/core/KotlinWriter.kt

@@ -320,7 +320,7 @@ class KotlinPropertyFormatter(
             is Symbol -> {
                 writer.addImport(type)
                 var formatted = if (fullyQualifiedNames) type.fullName else type.name
-                if (includeNullability && type.isBoxed) {
+                if (includeNullability && type.isNullable) {
                     formatted += "?"
                 }
 

codegen/smithy-kotlin-codegen/src/main/kotlin/software/amazon/smithy/kotlin/codegen/model/SymbolBuilder.kt

@@ -78,7 +78,7 @@ open class SymbolBuilder {
     fun build(): Symbol {
         builder.name(name)
         if (nullable) {
-            builder.boxed()
+            builder.nullable()
         }
         builder.putProperty(SymbolProperty.IS_EXTENSION, isExtension)
         if (objectRef != null) {

codegen/smithy-kotlin-codegen/src/main/kotlin/software/amazon/smithy/kotlin/codegen/model/SymbolExt.kt

@@ -18,8 +18,11 @@ object SymbolProperty {
     // The key that holds the default value for a type (symbol) as a string
     const val DEFAULT_VALUE_KEY: String = "defaultValue"
 
-    // Boolean property indicating this symbol should be boxed
-    const val BOXED_KEY: String = "boxed"
+    // The key that holds the type of default value
+    const val DEFAULT_VALUE_TYPE_KEY: String = "defaultValueType"
+
+    // Boolean property indicating this symbol is nullable
+    const val NULLABLE_KEY: String = "nullable"
 
     // the original shape the symbol was created from
     const val SHAPE_KEY: String = "shape"
@@ -47,21 +50,21 @@ object SymbolProperty {
 }
 
 /**
- * Test if a symbol is boxed
+ * Test if a symbol is nullable
  */
-val Symbol.isBoxed: Boolean
-    get() = getProperty(SymbolProperty.BOXED_KEY).map {
+val Symbol.isNullable: Boolean
+    get() = getProperty(SymbolProperty.NULLABLE_KEY).map {
         when (it) {
             is Boolean -> it
             else -> false
         }
     }.orElse(false)
 
 /**
- * Test if a symbol is not boxed
+ * Test if a symbol is not nullable
  */
-val Symbol.isNotBoxed: Boolean
-    get() = !isBoxed
+val Symbol.isNotNullable: Boolean
+    get() = !isNullable
 
 enum class PropertyTypeMutability {
     /**
@@ -82,6 +85,21 @@ enum class PropertyTypeMutability {
     }
 }
 
+enum class DefaultValueType {
+    /**
+     * A default value which has been inferred, such as 0f for floats and false for booleans
+     */
+    INFERRED,
+
+    /**
+     * A default value which has been modeled using Smithy's default trait.
+     */
+    MODELED,
+}
+
+val Symbol.defaultValueType: DefaultValueType?
+    get() = getProperty(SymbolProperty.DEFAULT_VALUE_TYPE_KEY, DefaultValueType::class.java).getOrNull()
+
 /**
  * Get the property type mutability of this symbol if set.
  */
@@ -92,27 +110,30 @@ val Symbol.propertyTypeMutability: PropertyTypeMutability?
 
 /**
  * Gets the default value for the symbol if present, else null
- * @param defaultBoxed the string to pass back for boxed values
+ * @param defaultNullable the string to pass back for nullable values
  */
-fun Symbol.defaultValue(defaultBoxed: String? = "null"): String? {
-    // boxed types should always be defaulted to null
-    if (isBoxed) {
-        return defaultBoxed
-    }
-
+fun Symbol.defaultValue(defaultNullable: String? = "null"): String? {
     val default = getProperty(SymbolProperty.DEFAULT_VALUE_KEY, String::class.java)
-    return if (default.isPresent) default.get() else null
+
+    // nullable types should default to null if there is no modeled default
+    if (isNullable && (!default.isPresent || defaultValueType == DefaultValueType.INFERRED)) {
+        return defaultNullable
+    }
+    return default.getOrNull()
 }
 
 /**
- * Mark a symbol as being boxed (nullable) i.e. `T?`
+ * Mark a symbol as being nullable (i.e. `T?`)
  */
-fun Symbol.Builder.boxed(): Symbol.Builder = apply { putProperty(SymbolProperty.BOXED_KEY, true) }
+fun Symbol.Builder.nullable(): Symbol.Builder = apply { putProperty(SymbolProperty.NULLABLE_KEY, true) }
 
 /**
  * Set the default value used when formatting the symbol
  */
-fun Symbol.Builder.defaultValue(value: String): Symbol.Builder = apply { putProperty(SymbolProperty.DEFAULT_VALUE_KEY, value) }
+fun Symbol.Builder.defaultValue(value: String?, type: DefaultValueType = DefaultValueType.INFERRED): Symbol.Builder = apply {
+    putProperty(SymbolProperty.DEFAULT_VALUE_KEY, value)
+    putProperty(SymbolProperty.DEFAULT_VALUE_TYPE_KEY, type)
+}
 
 /**
  * Convenience function for specifying kotlin namespace
@@ -177,7 +198,7 @@ val Symbol.shape: Shape?
 /**
  * Get the nullable version of a symbol
  */
-fun Symbol.asNullable(): Symbol = toBuilder().boxed().build()
+fun Symbol.asNullable(): Symbol = toBuilder().nullable().build()
 
 /**
  * Check whether a symbol represents an extension

codegen/smithy-kotlin-codegen/src/main/kotlin/software/amazon/smithy/kotlin/codegen/rendering/StructureGenerator.kt

@@ -170,7 +170,7 @@ class StructureGenerator(
     // Return the appropriate hashCode fragment based on ShapeID of member target.
     private fun selectHashFunctionForShape(member: MemberShape): String {
         val targetShape = model.expectShape(member.target)
-        val isNullable = memberNameSymbolIndex[member]!!.second.isBoxed
+        val isNullable = memberNameSymbolIndex[member]!!.second.isNullable
         return when (targetShape.type) {
             ShapeType.INTEGER ->
                 when (isNullable) {

codegen/smithy-kotlin-codegen/src/main/kotlin/software/amazon/smithy/kotlin/codegen/rendering/UnionGenerator.kt

@@ -10,7 +10,7 @@ import software.amazon.smithy.kotlin.codegen.core.*
 import software.amazon.smithy.kotlin.codegen.lang.KotlinTypes
 import software.amazon.smithy.kotlin.codegen.model.filterEventStreamErrors
 import software.amazon.smithy.kotlin.codegen.model.hasTrait
-import software.amazon.smithy.kotlin.codegen.model.isBoxed
+import software.amazon.smithy.kotlin.codegen.model.isNullable
 import software.amazon.smithy.model.Model
 import software.amazon.smithy.model.shapes.*
 import software.amazon.smithy.model.traits.SensitiveTrait
@@ -126,12 +126,12 @@ class UnionGenerator(
 
         return when (targetShape.type) {
             ShapeType.INTEGER ->
-                when (targetSymbol.isBoxed) {
+                when (targetSymbol.isNullable) {
                     true -> " ?: 0"
                     else -> ""
                 }
             ShapeType.BYTE ->
-                when (targetSymbol.isBoxed) {
+                when (targetSymbol.isNullable) {
                     true -> ".toInt() ?: 0"
                     else -> ".toInt()"
                 }
@@ -144,7 +144,7 @@ class UnionGenerator(
                     ".contentHashCode()"
                 }
             else ->
-                when (targetSymbol.isBoxed) {
+                when (targetSymbol.isNullable) {
                     true -> ".hashCode() ?: 0"
                     else -> ".hashCode()"
                 }

codegen/smithy-kotlin-codegen/src/main/kotlin/software/amazon/smithy/kotlin/codegen/rendering/protocol/HttpBindingProtocolGenerator.kt

@@ -703,7 +703,7 @@ abstract class HttpBindingProtocolGenerator : ProtocolGenerator {
             val headerName = hdrBinding.locationName
 
             val targetSymbol = ctx.symbolProvider.toSymbol(hdrBinding.member)
-            val defaultValuePostfix = if (targetSymbol.isNotBoxed && targetSymbol.defaultValue() != null) {
+            val defaultValuePostfix = if (targetSymbol.isNotNullable && targetSymbol.defaultValue() != null) {
                 " ?: ${targetSymbol.defaultValue()}"
             } else {
                 ""