Fix toString for Scala 3 enums with no parameters

build.sbt

@@ -106,7 +106,7 @@ val betterToString =
     .settings(
       commonSettings,
       (publish / skip) := true,
-      addCommandAlias("generateAll", List("githubWorkflowGenerate", "mergifyWrite", "readmeWrite").mkString(";"))
+      addCommandAlias("generateAll", List("githubWorkflowGenerate", "mergifyWrite", "readmeWrite", "headerCreateAll").mkString(";"))
     )
     .aggregate(plugin, tests)
     .enablePlugins(NoPublishPlugin)

plugin/src/main/scala-2/Scala2CompilerApi.scala

@@ -106,14 +106,24 @@ object Scala2CompilerApi {
         case d: ValDef => d.name.toString
       }
 
-      def isCaseClass(clazz: Clazz): Boolean = clazz.merge.mods.isCase
+      // No enums in scala 2
+      def isEnum(clazz: Clazz): Boolean = false
+
+      def isViableDefinition(clazz: Clazz): Boolean = {
+        val isCaseClassOrObject = clazz.merge.mods.isCase
+
+        isCaseClassOrObject
+      }
 
       // Always return true for ModuleDef - apparently ModuleDef doesn't have the module flag...
       def isObject(clazz: Clazz): Boolean = clazz.fold(
         clazz = _.mods.hasModuleFlag,
         obj = _ => true
       )
 
+      def productPrefixParam: Nothing = sys.error("invalid state: this shouldn't be called in Scala 2")
+
+      def report(str: String): Unit = reporter.echo(str)
     }
 
 }

plugin/src/main/scala-3.1.x/ParentTypes.scala

@@ -0,0 +1,31 @@
+/*
+ * Copyright 2020 Polyvariant
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.polyvariant
+
+import dotty.tools.dotc.core.Symbols.ClassSymbol
+import dotty.tools.dotc.core.Contexts.Context
+import dotty.tools.dotc.core.Types.Type
+import dotty.tools.dotc.core.Types.ClassInfo
+
+extension (clazz: ClassSymbol) {
+
+  // 3.1.x/3.2.x doesn't have this method, this is the inlined definition from 3.3.x
+  def parentTypes(using Context): List[Type] = clazz.info match
+    case classInfo: ClassInfo => classInfo.declaredParents
+    case _                    => Nil
+
+}

plugin/src/main/scala-3.2.x/ParentTypes.scala

@@ -0,0 +1,31 @@
+/*
+ * Copyright 2020 Polyvariant
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.polyvariant
+
+import dotty.tools.dotc.core.Symbols.ClassSymbol
+import dotty.tools.dotc.core.Contexts.Context
+import dotty.tools.dotc.core.Types.Type
+import dotty.tools.dotc.core.Types.ClassInfo
+
+extension (clazz: ClassSymbol) {
+
+  // 3.1.x/3.2.x doesn't have this method, this is the inlined definition from 3.3.x
+  def parentTypes(using Context): List[Type] = clazz.info match
+    case classInfo: ClassInfo => classInfo.declaredParents
+    case _                    => Nil
+
+}

plugin/src/main/scala-3/Scala3CompilerApi.scala

@@ -94,11 +94,22 @@ object Scala3CompilerApi:
         d.name.toString
       }
 
-    def isCaseClass(clazz: Clazz): Boolean =
-      // for some reason, this is true for case objects too
-      clazz.clazz.flags.is(CaseClass)
+    def isEnum(clazz: Clazz): Boolean =
+      // the class is an enum if its direct supertypes include scala.reflect.Enum
+      clazz.clazz.parentTypes.map(_.typeSymbol).contains(Symbols.defn.EnumClass)
+
+    def isViableDefinition(clazz: Clazz): Boolean = {
+      val isCaseClassOrObject = clazz.clazz.flags.is(CaseClass)
+
+      isCaseClassOrObject || isEnum(clazz)
+    }
 
     def isObject(clazz: Clazz): Boolean =
       clazz.clazz.flags.is(Module)
 
+    def report(str: String): Unit =
+      dotty.tools.dotc.report.echo(str)
+
+    def productPrefixParam: ParamName = "productPrefix".toTermName
+
 end Scala3CompilerApi

plugin/src/main/scala/BetterToStringImpl.scala

@@ -39,9 +39,13 @@ trait CompilerApi {
   def createToString(clazz: Clazz, body: Tree): Method
   def addMethod(clazz: Clazz, method: Method): Clazz
   def methodNames(clazz: Clazz): List[String]
-  // better name: "is case class or object"
-  def isCaseClass(clazz: Clazz): Boolean
+  def isViableDefinition(clazz: Clazz): Boolean
+  def isEnum(clazz: Clazz): Boolean
   def isObject(clazz: Clazz): Boolean
+  def productPrefixParam: ParamName
+
+  // debugging
+  def report(str: String): Unit
 }
 
 trait BetterToStringImpl[+C <: CompilerApi] {
@@ -73,7 +77,7 @@ object BetterToStringImpl {
         // technically, the method found by this can be even something like "def toString(s: String): Unit", but we're ignoring that
         val hasToString: Boolean = methodNames(clazz).contains("toString")
 
-        val shouldModify = isCaseClass(clazz) && !isNested && !hasToString
+        val shouldModify = isViableDefinition(clazz) && !isNested && !hasToString
 
         if (shouldModify) overrideToString(clazz, enclosingObject)
         else clazz
@@ -101,6 +105,7 @@ object BetterToStringImpl {
 
         val paramParts =
           if (api.isObject(clazz)) Nil
+          else if (api.isEnum(clazz)) List(literalConstant("."), selectInThis(clazz, productPrefixParam))
           else
             List(
               List(literalConstant("(")),

tests/src/test/scala-3/Scala3Tests.scala

@@ -20,15 +20,11 @@ class Scala3Tests extends FunSuite:
   test("an enum made of constants should have a normal toString") {
     assertEquals(
       ScalaVersion.Scala2.toString,
-      // https://github.com/polyvariant/better-tostring/issues/60
-      // should be "ScalaVersion.Scala2"
-      "Scala2"
+      "ScalaVersion.Scala2"
     )
     assertEquals(
       ScalaVersion.Scala3.toString,
-      // https://github.com/polyvariant/better-tostring/issues/60
-      // should be "ScalaVersion.Scala3"
-      "Scala3"
+      "ScalaVersion.Scala3"
     )
   }
 
@@ -39,9 +35,7 @@ class Scala3Tests extends FunSuite:
     )
     assertEquals(
       User.Unauthorized.toString,
-      // https://github.com/polyvariant/better-tostring/issues/60
-      // should be "User.Unauthorized"
-      "Unauthorized"
+      "User.Unauthorized"
     )
   }