Validate default parameter values

burst-kotlin-plugin-tests/src/test/kotlin/app/cash/burst/kotlin/BurstKotlinPluginTest.kt

@@ -106,6 +106,33 @@ class BurstKotlinPluginTest {
       .contains("CoffeeTest.kt:7:12 Expected an enum for @Burst test parameter")
   }
 
+  @Test
+  fun unexpectedDefaultArgumentValue() {
+    val result = compile(
+      sourceFile = SourceFile.kotlin(
+        "CoffeeTest.kt",
+        """
+        import app.cash.burst.Burst
+        import kotlin.test.Test
+
+        val defaultEspresso = Espresso.Regular
+
+        @Burst
+        class CoffeeTest {
+          @Test
+          fun test(espresso: Espresso = defaultEspresso) {
+          }
+        }
+
+        enum class Espresso { Decaf, Regular, Double }
+        """,
+      ),
+    )
+    assertEquals(KotlinCompilation.ExitCode.COMPILATION_ERROR, result.exitCode, result.messages)
+    assertThat(result.messages)
+      .contains("CoffeeTest.kt:9:12 @Burst default parameter must be an enum constant (or absent)")
+  }
+
   @Test
   fun constructorParameters() {
     val result = compile(

burst-kotlin-plugin/src/main/kotlin/app/cash/burst/kotlin/Argument.kt

@@ -61,7 +61,18 @@ internal fun IrPluginContext.allPossibleArguments(
   val referenceClass = referenceClass(classId)?.owner ?: return null
   if (!referenceClass.isEnumClass) return null
   val enumEntries = referenceClass.declarations.filterIsInstance<IrEnumEntry>()
-  val defaultValueSymbol = (parameter.defaultValue?.expression as? IrGetEnumValue)?.symbol
+
+  val defaultValueSymbol = parameter.defaultValue?.let { defaultValue ->
+    val expression = defaultValue.expression
+    if (expression !is IrGetEnumValue) {
+      throw BurstCompilationException(
+        "@Burst default parameter must be an enum constant (or absent)",
+        parameter,
+      )
+    }
+    expression.symbol
+  }
+
   return enumEntries.map {
     Argument(
       original = parameter,

burst-kotlin-plugin/src/main/kotlin/app/cash/burst/kotlin/package.kt

@@ -1,6 +1,5 @@
 package app.cash.burst.kotlin
 
-import org.jetbrains.kotlin.name.CallableId
 import org.jetbrains.kotlin.name.ClassId
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.Name
@@ -9,18 +8,6 @@ import org.jetbrains.kotlin.name.Name
 @JvmInline
 value class FqPackageName(val fqName: FqName)
 
-fun FqPackageName(name: String): FqPackageName {
-  return FqPackageName(FqName(name))
-}
+fun FqPackageName(name: String) = FqPackageName(FqName(name))
 
-fun FqPackageName.classId(name: String): ClassId {
-  return ClassId(fqName, Name.identifier(name))
-}
-
-fun FqPackageName.callableId(name: String): CallableId {
-  return CallableId(fqName, Name.identifier(name))
-}
-
-fun ClassId.callableId(name: String): CallableId {
-  return CallableId(this, Name.identifier(name))
-}
+fun FqPackageName.classId(name: String) = ClassId(fqName, Name.identifier(name))