Various improvements for Scala 3 macro to match Scala 2 implementation (

#148)

These issues were found while porting Mill to Scala 3.

example/optseq/src/Main.scala

@@ -1,5 +1,5 @@
 package example.optseq
-import mainargs.{main, arg, ParserForMethods, ArgReader}
+import mainargs.{main, arg, ParserForMethods, TokensReader}
 
 object Main {
   @main

mainargs/src-3/Macros.scala

@@ -32,23 +32,34 @@ object Macros {
     val companionModuleType = typeSymbolOfB.companionModule.tree.asInstanceOf[ValDef].tpt.tpe.asType
     val companionModuleExpr = Ident(companionModule).asExpr
     val mainAnnotationInstance = typeSymbolOfB.getAnnotation(mainAnnotation).getOrElse {
-      report.throwError(
-        s"cannot find @main annotation on ${companionModule.name}",
-        typeSymbolOfB.pos.get
+      '{new mainargs.main()}.asTerm // construct a default if not found.
+    }
+    val ctor = typeSymbolOfB.primaryConstructor
+    val ctorParams = ctor.paramSymss.flatten
+    // try to match the apply method with the constructor parameters, this is a good heuristic
+    // for if the apply method is overloaded.
+    val annotatedMethod = typeSymbolOfB.companionModule.memberMethod("apply").filter(p =>
+      p.paramSymss.flatten.corresponds(ctorParams) { (p1, p2) =>
+        p1.name == p2.name
+      }
+    ).headOption.getOrElse {
+      report.errorAndAbort(
+        s"Cannot find apply method in companion object of ${typeReprOfB.show}",
+        typeSymbolOfB.companionModule.pos.getOrElse(Position.ofMacroExpansion)
       )
     }
-    val annotatedMethod = TypeRepr.of[B].typeSymbol.companionModule.memberMethod("apply").head
     companionModuleType match
       case '[bCompanion] =>
-        val mainData = createMainData[B, Any](
+        val mainData = createMainData[B, bCompanion](
           annotatedMethod,
           mainAnnotationInstance,
           // Somehow the `apply` method parameter annotations don't end up on
           // the `apply` method parameters, but end up in the `<init>` method
           // parameters, so use those for getting the annotations instead
           TypeRepr.of[B].typeSymbol.primaryConstructor.paramSymss
         )
-        '{ new ParserForClass[B](${ mainData }, () => ${ Ident(companionModule).asExpr }) }
+        val erasedMainData = '{$mainData.asInstanceOf[MainData[B, Any]]}
+        '{ new ParserForClass[B]($erasedMainData, () => ${ Ident(companionModule).asExpr }) }
   }
 
   def createMainData[T: Type, B: Type](using Quotes)
@@ -57,41 +68,84 @@ object Macros {
     createMainData[T, B](method, mainAnnotation, method.paramSymss)
   }
 
+  private object VarargTypeRepr {
+    def unapply(using Quotes)(tpe: quotes.reflect.TypeRepr): Option[quotes.reflect.TypeRepr] = {
+      import quotes.reflect.*
+      tpe match {
+        case AnnotatedType(AppliedType(_, Seq(arg)), x)
+          if x.tpe =:= defn.RepeatedAnnot.typeRef => Some(arg)
+        case _ => None
+      }
+    }
+  }
+
+  private object AsType {
+    def unapply(using Quotes)(tpe: quotes.reflect.TypeRepr): Some[Type[?]] = {
+      Some(tpe.asType)
+    }
+  }
+
   def createMainData[T: Type, B: Type](using Quotes)
                                       (method: quotes.reflect.Symbol,
                                        mainAnnotation: quotes.reflect.Term,
                                        annotatedParamsLists: List[List[quotes.reflect.Symbol]]): Expr[MainData[T, B]] = {
 
     import quotes.reflect.*
     val params = method.paramSymss.headOption.getOrElse(report.throwError("Multiple parameter lists not supported"))
-    val defaultParams = getDefaultParams(method)
+    val defaultParams = if (params.exists(_.flags.is(Flags.HasDefault))) getDefaultParams(method) else Map.empty
     val argSigsExprs = params.zip(annotatedParamsLists.flatten).map { paramAndAnnotParam =>
       val param = paramAndAnnotParam._1
       val annotParam = paramAndAnnotParam._2
       val paramTree = param.tree.asInstanceOf[ValDef]
       val paramTpe = paramTree.tpt.tpe
+      val readerTpe = paramTpe match {
+        case VarargTypeRepr(AsType('[t])) => TypeRepr.of[Leftover[t]]
+        case _ => paramTpe
+      }
       val arg = annotParam.getAnnotation(argAnnotation).map(_.asExprOf[mainargs.arg]).getOrElse('{ new mainargs.arg() })
-      val paramType = paramTpe.asType
-      paramType match
+      readerTpe.asType match {
         case '[t] =>
+          def applyAndCast(f: Expr[Any] => Expr[Any], arg: Expr[B]): Expr[t] = {
+            f(arg) match {
+              case '{ $v: `t` } => v
+              case expr => {
+                // this case will be activated when the found default parameter is not of type `t`
+                val recoveredType =
+                  try
+                    expr.asExprOf[t]
+                  catch
+                    case err: Exception =>
+                      report.errorAndAbort(
+                        s"""Failed to convert default value for parameter ${param.name},
+                        |expected type: ${paramTpe.show},
+                        |but default value ${expr.show} is of type: ${expr.asTerm.tpe.widen.show}
+                        |while converting type caught an exception with message: ${err.getMessage}
+                        |There might be a bug in mainargs.""".stripMargin,
+                        param.pos.getOrElse(Position.ofMacroExpansion)
+                      )
+                recoveredType
+              }
+            }
+          }
           val defaultParam: Expr[Option[B => t]] = defaultParams.get(param) match {
-            case Some('{ $v: `t`}) => '{ Some(((_: B) => $v)) }
+            case Some(f) => '{ Some((b: B) => ${ applyAndCast(f, 'b) }) }
             case None => '{ None }
           }
           val tokensReader = Expr.summon[mainargs.TokensReader[t]].getOrElse {
-            report.throwError(
-              s"No mainargs.ArgReader found for parameter ${param.name}",
-              param.pos.get
+            report.errorAndAbort(
+              s"No mainargs.TokensReader[${Type.show[t]}] found for parameter ${param.name} of method ${method.name} in ${method.owner.fullName}",
+              method.pos.getOrElse(Position.ofMacroExpansion)
             )
           }
           '{ (ArgSig.create[t, B](${ Expr(param.name) }, ${ arg }, ${ defaultParam })(using ${ tokensReader })) }
+      }
     }
     val argSigs = Expr.ofList(argSigsExprs)
 
     val invokeRaw: Expr[(B, Seq[Any]) => T] = {
 
       def callOf(methodOwner: Expr[Any], args: Expr[Seq[Any]]) =
-        call(methodOwner, method, '{ Seq($args) }).asExprOf[T]
+        call(methodOwner, method, args).asExprOf[T]
 
       '{ (b: B, params: Seq[Any]) => ${ callOf('b, 'params) } }
     }
@@ -120,37 +174,50 @@ object Macros {
   private def call(using Quotes)(
       methodOwner: Expr[Any],
       method: quotes.reflect.Symbol,
-      argss: Expr[Seq[Seq[Any]]]
+      args: Expr[Seq[Any]]
   ): Expr[_] = {
     // Copy pasted from Cask.
     // https://github.com/com-lihaoyi/cask/blob/65b9c8e4fd528feb71575f6e5ef7b5e2e16abbd9/cask/src-3/cask/router/Macros.scala#L106
     import quotes.reflect._
     val paramss = method.paramSymss
 
     if (paramss.isEmpty) {
-      report.throwError("At least one parameter list must be declared.", method.pos.get)
+      report.errorAndAbort("At least one parameter list must be declared.", method.pos.get)
     }
-
-    val accesses: List[List[Term]] = for (i <- paramss.indices.toList) yield {
-      for (j <- paramss(i).indices.toList) yield {
-        val tpe = paramss(i)(j).tree.asInstanceOf[ValDef].tpt.tpe
-        tpe.asType match
-          case '[t] => '{ $argss(${Expr(i)})(${Expr(j)}).asInstanceOf[t] }.asTerm
-      }
+    if (paramss.sizeIs > 1) {
+      report.errorAndAbort("Multiple parameter lists are not supported.", method.pos.get)
     }
+    val params = paramss.head
+
+    val methodType = methodOwner.asTerm.tpe.memberType(method)
+
+    def accesses(ref: Expr[Seq[Any]]): List[Term] =
+      for (i <- params.indices.toList) yield {
+        val param = params(i)
+        val tpe = methodType.memberType(param)
+        val untypedRef = '{ $ref(${Expr(i)}) }
+        tpe match {
+          case VarargTypeRepr(AsType('[t])) =>
+            Typed(
+              '{ $untypedRef.asInstanceOf[Leftover[t]].value }.asTerm,
+              Inferred(AppliedType(defn.RepeatedParamClass.typeRef, List(TypeRepr.of[t])))
+            )
+          case _ => tpe.asType match
+            case '[t] => '{ $untypedRef.asInstanceOf[t] }.asTerm
+        }
+      }
 
-    methodOwner.asTerm.select(method).appliedToArgss(accesses).asExpr
+    methodOwner.asTerm.select(method).appliedToArgs(accesses(args)).asExpr
   }
-
 
   /** Lookup default values for a method's parameters. */
-  private def getDefaultParams(using Quotes)(method: quotes.reflect.Symbol): Map[quotes.reflect.Symbol, Expr[Any]] = {
+  private def getDefaultParams(using Quotes)(method: quotes.reflect.Symbol): Map[quotes.reflect.Symbol, Expr[Any] => Expr[Any]] = {
     // Copy pasted from Cask.
     // https://github.com/com-lihaoyi/cask/blob/65b9c8e4fd528feb71575f6e5ef7b5e2e16abbd9/cask/src-3/cask/router/Macros.scala#L38
     import quotes.reflect._
 
     val params = method.paramSymss.flatten
-    val defaults = collection.mutable.Map.empty[Symbol, Expr[Any]]
+    val defaults = collection.mutable.Map.empty[Symbol, Expr[Any] => Expr[Any]]
 
     val Name = (method.name + """\$default\$(\d+)""").r
     val InitName = """\$lessinit\$greater\$default\$(\d+)""".r
@@ -159,13 +226,13 @@ object Macros {
 
     idents.foreach{
       case deff @ DefDef(Name(idx), _, _, _) =>
-        val expr = Ref(deff.symbol).asExpr
+        val expr = (owner: Expr[Any]) => Select(owner.asTerm, deff.symbol).asExpr
         defaults += (params(idx.toInt - 1) -> expr)
 
       // The `apply` method re-uses the default param factory methods from `<init>`,
       // so make sure to check if those exist too
       case deff @ DefDef(InitName(idx), _, _, _) if method.name == "apply" =>
-        val expr = Ref(deff.symbol).asExpr
+        val expr = (owner: Expr[Any]) => Select(owner.asTerm, deff.symbol).asExpr
         defaults += (params(idx.toInt - 1) -> expr)
 
       case _ =>

mainargs/test/src/ClassTests.scala

@@ -12,9 +12,56 @@ object ClassTests extends TestSuite {
   @main
   case class Qux(moo: String, b: Bar)
 
+  case class Cli(@arg(short = 'd') debug: Flag)
+
+  @main
+  class Compat(
+      @arg(short = 'h') val home: String,
+      @arg(short = 's') val silent: Flag,
+      val leftoverArgs: Leftover[String]
+  ) {
+    override def equals(obj: Any): Boolean =
+      obj match {
+        case c: Compat =>
+          home == c.home && silent == c.silent && leftoverArgs == c.leftoverArgs
+        case _ => false
+      }
+  }
+  object Compat {
+    def apply(
+        home: String = "/home",
+        silent: Flag = Flag(),
+        leftoverArgs: Leftover[String] = Leftover()
+    ) = new Compat(home, silent, leftoverArgs)
+
+    @deprecated("bin-compat shim", "0.1.0")
+    private[mainargs] def apply(
+        home: String,
+        silent: Flag,
+        noDefaultPredef: Flag,
+        leftoverArgs: Leftover[String]
+    ) = new Compat(home, silent, leftoverArgs)
+  }
+
   implicit val fooParser: ParserForClass[Foo] = ParserForClass[Foo]
   implicit val barParser: ParserForClass[Bar] = ParserForClass[Bar]
   implicit val quxParser: ParserForClass[Qux] = ParserForClass[Qux]
+  implicit val cliParser: ParserForClass[Cli] = ParserForClass[Cli]
+  implicit val compatParser: ParserForClass[Compat] = ParserForClass[Compat]
+
+  class PathWrap {
+    @main
+    case class Foo(x: Int = 23, y: Int = 47)
+
+    object Main {
+      @main
+      def run(bar: Bar, bool: Boolean = false) = {
+        s"${bar.w.value} ${bar.f.x} ${bar.f.y} ${bar.zzzz} $bool"
+      }
+    }
+
+    implicit val fooParser: ParserForClass[Foo] = ParserForClass[Foo]
+  }
 
   object Main {
     @main
@@ -161,5 +208,27 @@ object ClassTests extends TestSuite {
         Seq("-x", "1", "-y", "2", "-z", "hello")
       ) ==> "false 1 2 hello false"
     }
+    test("mill-compat") {
+      test("apply-overload-class") {
+        compatParser.constructOrThrow(Seq("foo")) ==> Compat(
+          home = "/home",
+          silent = Flag(false),
+          leftoverArgs = Leftover("foo")
+        )
+      }
+      test("no-main-on-class") {
+        cliParser.constructOrThrow(Seq("-d")) ==> Cli(Flag(true))
+      }
+      test("path-dependent-default") {
+        val p = new PathWrap
+        p.fooParser.constructOrThrow(Seq()) ==> p.Foo(23, 47)
+      }
+      test("path-dependent-default-method") {
+        val p = new PathWrap
+        ParserForMethods(p.Main).runOrThrow(
+          Seq("-x", "1", "-y", "2", "-z", "hello")
+        ) ==> "false 1 2 hello false"
+      }
+    }
   }
 }

mainargs/test/src-2/VarargsOldTests.scala → mainargs/test/src/VarargsOldTests.scala

@@ -9,7 +9,7 @@ object VarargsOldTests extends VarargsBaseTests {
 
     @main
     def mixedVariadic(@arg(short = 'f') first: Int, args: String*) =
-      first + args.mkString
+      first.toString + args.mkString
   }
 
   val check = new Checker(ParserForMethods(Base), allowPositional = true)