Add smol caching & a utility method

workflow-core/src/commonMain/kotlin/com/squareup/workflow1/WorkflowIdentifier.kt

@@ -9,6 +9,7 @@ import okio.Buffer
 import okio.ByteString
 import okio.EOFException
 import kotlin.LazyThreadSafetyMode.PUBLICATION
+import kotlin.concurrent.Volatile
 import kotlin.jvm.JvmMultifileClass
 import kotlin.jvm.JvmName
 import kotlin.reflect.KClass
@@ -58,6 +59,17 @@ public class WorkflowIdentifier internal constructor(
 
   private val proxiedIdentifiers = generateSequence(this) { it.proxiedIdentifier }
 
+  @Volatile
+  private var cachedToString: String? = null
+
+  /**
+   * Either a [KClass] or [KType] representing the "real" type that this identifier
+   * identifies – i.e. which is not an [ImpostorWorkflow].
+   */
+  public val realType: WorkflowIdentifierType by lazy(PUBLICATION) {
+    proxiedIdentifiers.last().type
+  }
+
   /**
    * If this identifier is snapshottable, returns the serialized form of the identifier.
    * If it is not snapshottable, returns null.
@@ -83,23 +95,24 @@ public class WorkflowIdentifier internal constructor(
     }
   }
 
-  /**
-   * Returns either a [KClass] or [KType] representing the "real" type that this identifier
-   * identifies – i.e. which is not an [ImpostorWorkflow].
-   */
-  public fun getRealIdentifierType(): WorkflowIdentifierType = proxiedIdentifiers.last().type
+  @Deprecated("This is now a lazily computed val", ReplaceWith("realType"))
+  public fun getRealIdentifierType(): WorkflowIdentifierType = realType
 
   /**
    * If this identifier identifies an [ImpostorWorkflow], returns the result of that workflow's
    * [ImpostorWorkflow.describeRealIdentifier] method, otherwise returns a description of this
    * identifier including the name of its workflow type and any [ImpostorWorkflow.realIdentifier]s.
    *
    */
-  override fun toString(): String =
-    description?.invoke()
+  override fun toString(): String {
+    return cachedToString ?: (description?.invoke()
       ?: proxiedIdentifiers
         .joinToString { it.typeName }
-        .let { "WorkflowIdentifier($it)" }
+        .let { "WorkflowIdentifier($it)" })
+      .also {
+        cachedToString = it
+      }
+  }
 
   override fun equals(other: Any?): Boolean = when {
     this === other -> true

workflow-core/src/commonTest/kotlin/com/squareup/workflow1/WorkflowIdentifierTest.kt

@@ -153,22 +153,22 @@ internal class WorkflowIdentifierTest {
 
   @Test fun getRealIdentifierType_returns_self_for_non_impostor_workflow() {
     val id = TestWorkflow1.identifier
-    assertEquals(Snapshottable(TestWorkflow1::class), id.getRealIdentifierType())
+    assertEquals(Snapshottable(TestWorkflow1::class), id.realType)
   }
 
   @Test fun getRealIdentifierType_returns_real_identifier_for_impostor_workflow() {
     val id = TestImpostor1(TestWorkflow1).identifier
-    assertEquals(Snapshottable(TestWorkflow1::class), id.getRealIdentifierType())
+    assertEquals(Snapshottable(TestWorkflow1::class), id.realType)
   }
 
   @Test fun getRealIdentifierType_returns_leaf_real_identifier_for_impostor_workflow_chain() {
     val id = TestImpostor2(TestImpostor1(TestWorkflow1)).identifier
-    assertEquals(Snapshottable(TestWorkflow1::class), id.getRealIdentifierType())
+    assertEquals(Snapshottable(TestWorkflow1::class), id.realType)
   }
 
   @Test fun getRealIdentifierType_returns_KType_of_unsnapshottable_identifier() {
     val id = TestUnsnapshottableImpostor(typeOf<List<String>>()).identifier
-    assertEquals(Unsnapshottable(typeOf<List<String>>()), id.getRealIdentifierType())
+    assertEquals(Unsnapshottable(typeOf<List<String>>()), id.realType)
   }
 
   public object TestWorkflow1 : Workflow<Nothing, Nothing, Nothing> {

workflow-runtime/src/commonMain/kotlin/com/squareup/workflow1/WorkflowInterceptor.kt

@@ -152,6 +152,12 @@ public interface WorkflowInterceptor {
     /** The parent [WorkflowSession] of this workflow, or null if this is the root workflow. */
     public val parent: WorkflowSession?
 
+    /**
+     * true if this is the root workflow, in which case [parent] is null.
+     */
+    public val isRootWorkflow: Boolean
+      get() = parent == null
+
     /** The [RuntimeConfig] of the runtime this session is executing in. */
     public val runtimeConfig: RuntimeConfig
   }

workflow-testing/src/main/java/com/squareup/workflow1/testing/RealRenderTester.kt

@@ -360,8 +360,8 @@ internal fun createRenderChildInvocation(
 internal fun WorkflowIdentifier.realTypeMatchesExpectation(
   expected: WorkflowIdentifier
 ): Boolean {
-  val expectedType = expected.getRealIdentifierType()
-  val actualType = getRealIdentifierType()
+  val expectedType = expected.realType
+  val actualType = realType
   return actualType.matchesExpectation(expectedType)
 }
 

workflow-tracing/src/main/java/com/squareup/workflow1/diagnostic/tracing/TracingWorkflowInterceptor.kt

@@ -494,7 +494,7 @@ public class TracingWorkflowInterceptor internal constructor(
 }
 
 private fun WorkflowIdentifier.toLoggingName(): String {
-  val type = getRealIdentifierType()
+  val type = realType
   return when {
     type is Snapshottable && type.kClass != null -> type.kClass!!.toLoggingName()
     type is Unsnapshottable -> type.kType.toLoggingName()