Simplify MainAnnotation interface

Remove the `Command` class and place the `argGetter`, `varargsGetter`
and `run` methods directly in the `MainAnnotation` interface.

Now `command` pre-processes the arguments which clearly states which
strings will be used for each argument. This simplifies the implementation
of the `MainAnnotation` methods.

Author: nicolasstucki

compiler/src/dotty/tools/dotc/ast/MainProxies.scala

@@ -141,29 +141,31 @@ object MainProxies {
    *       */
    *     @myMain(80) def f(
    *       @myMain.Alias("myX") x: S,
+   *       y: S,
    *       ys: T*
    *     ) = ...
    *
    *  would be translated to something like
    *
    *     final class f {
    *       static def main(args: Array[String]): Unit = {
-   *         val cmd = new myMain(80).command(
-   *           info = new CommandInfo(
-   *             name = "f",
-   *             documentation = "Lorem ipsum dolor sit amet consectetur adipiscing elit.",
-   *             parameters = Seq(
-   *               new scala.annotation.MainAnnotation.ParameterInfo("x", "S", false, false, "my param x", Seq(new scala.main.Alias("myX")))
-   *               new scala.annotation.MainAnnotation.ParameterInfo("ys", "T", false, false, "all my params y", Seq())
-   *             )
+   *         val annotation = new myMain(80)
+   *         val info = new Info(
+   *           name = "f",
+   *           documentation = "Lorem ipsum dolor sit amet consectetur adipiscing elit.",
+   *           parameters = Seq(
+   *             new scala.annotation.MainAnnotation.Parameter("x", "S", false, false, "my param x", Seq(new scala.main.Alias("myX"))),
+   *             new scala.annotation.MainAnnotation.Parameter("y", "S", true, false, "", Seq()),
+   *             new scala.annotation.MainAnnotation.Parameter("ys", "T", false, true, "all my params y", Seq())
    *           )
-   *           args = args
-   *         )
-   *
-   *         val args0: () => S = cmd.argGetter[S](0, None)
-   *         val args1: () => Seq[T] = cmd.varargGetter[T]
-   *
-   *         cmd.run(() => f(args0(), args1()*))
+   *         ),
+   *         val command = annotation.command(info, args)
+   *         if command.isDefined then
+   *           val cmd = command.get
+   *           val args0: () => S = annotation.argGetter[S](info.parameters(0), cmd(0), None)
+   *           val args1: () => S = annotation.argGetter[S](info.parameters(1), mainArgs(1), Some(() => sum$default$1()))
+   *           val args2: () => Seq[T] = annotation.varargGetter[T](info.parameters(2), cmd.drop(2))
+   *           annotation.run(() => f(args0(), args1(), args2()*))
    *       }
    *     }
    */
@@ -227,7 +229,7 @@ object MainProxies {
      *
      *  A ParamInfo has the following shape
      *  ```
-     *  new scala.annotation.MainAnnotation.ParameterInfo("x", "S", false, false, "my param x", Seq(new scala.main.Alias("myX")))
+     *  new scala.annotation.MainAnnotation.Parameter("x", "S", false, false, "my param x", Seq(new scala.main.Alias("myX")))
      *  ```
      */
     def parameterInfos(mt: MethodType): List[Tree] =
@@ -250,33 +252,34 @@ object MainProxies {
         val constructorArgs = List(param, paramTypeStr, hasDefault, isRepeated, paramDoc)
           .map(value => Literal(Constant(value)))
 
-        New(TypeTree(defn.MainAnnotationParameterInfo.typeRef), List(constructorArgs :+ paramAnnots))
+        New(TypeTree(defn.MainAnnotationParameter.typeRef), List(constructorArgs :+ paramAnnots))
 
     end parameterInfos
 
     /**
       * Creates a list of references and definitions of arguments.
       * The goal is to create the
-      *   `val args0: () => S = cmd.argGetter[S](0, None)`
+      *   `val args0: () => S = annotation.argGetter[S](0, cmd(0), None)`
       * part of the code.
       */
     def argValDefs(mt: MethodType): List[ValDef] =
       for ((formal, paramName), idx) <- mt.paramInfos.zip(mt.paramNames).zipWithIndex yield
-          val argName = nme.args ++ idx.toString
-          val isRepeated = formal.isRepeatedParam
-          val formalType = if isRepeated then formal.argTypes.head else formal
-          val getterName = if isRepeated then nme.varargGetter else nme.argGetter
-          val defaultValueGetterOpt = defaultValueSymbols.get(idx) match
-            case None => ref(defn.NoneModule.termRef)
-            case Some(dvSym) =>
-               val value = unitToValue(ref(dvSym.termRef))
-               Apply(ref(defn.SomeClass.companionModule.termRef), value)
-          val argGetter0 = TypeApply(Select(Ident(nme.cmd), getterName), TypeTree(formalType) :: Nil)
-          val argGetter =
-            if isRepeated then argGetter0
-            else Apply(argGetter0, List(Literal(Constant(idx)), defaultValueGetterOpt))
-
-          ValDef(argName, TypeTree(), argGetter)
+        val argName = nme.args ++ idx.toString
+        val isRepeated = formal.isRepeatedParam
+        val formalType = if isRepeated then formal.argTypes.head else formal
+        val getterName = if isRepeated then nme.varargGetter else nme.argGetter
+        val defaultValueGetterOpt = defaultValueSymbols.get(idx) match
+          case None => ref(defn.NoneModule.termRef)
+          case Some(dvSym) =>
+              val value = unitToValue(ref(dvSym.termRef))
+              Apply(ref(defn.SomeClass.companionModule.termRef), value)
+        val argGetter0 = TypeApply(Select(Ident(nme.annotation), getterName), TypeTree(formalType) :: Nil)
+        val index = Literal(Constant(idx))
+        val paramInfo = Apply(Select(Ident(nme.info), nme.parameters), index)
+        val argGetter =
+          if isRepeated then Apply(argGetter0, List(paramInfo, Apply(Select(Ident(nme.cmd), nme.drop), List(index))))
+          else Apply(argGetter0, List(paramInfo, Apply(Ident(nme.cmd), List(index)), defaultValueGetterOpt))
+        ValDef(argName, TypeTree(), argGetter)
     end argValDefs
 
 
@@ -316,18 +319,39 @@ object MainProxies {
         val nameTree = Literal(Constant(mainFun.showName))
         val docTree = Literal(Constant(documentation.mainDoc))
         val paramInfos = Apply(ref(defn.SeqModule.termRef), parameterInfos)
-        New(TypeTree(defn.MainAnnotationCommandInfo.typeRef), List(List(nameTree, docTree, paramInfos)))
+        New(TypeTree(defn.MainAnnotationInfo.typeRef), List(List(nameTree, docTree, paramInfos)))
 
-      val cmd = ValDef(
-        nme.cmd,
+      val annotVal = ValDef(
+        nme.annotation,
+        TypeTree(),
+        instantiateAnnotation(mainAnnot)
+      )
+      val infoVal = ValDef(
+        nme.info,
+        TypeTree(),
+        cmdInfo
+      )
+      val command = ValDef(
+        nme.command,
         TypeTree(),
         Apply(
-          Select(instantiateAnnotation(mainAnnot), nme.command),
-          List(cmdInfo, Ident(nme.args))
+          Select(Ident(nme.annotation), nme.command),
+          List(Ident(nme.info), Ident(nme.args))
         )
       )
-      val run = Apply(Select(Ident(nme.cmd), nme.run), mainCall)
-      val body = Block(cmdInfo :: cmd :: args, run)
+      val argsVal = ValDef(
+        nme.cmd,
+        TypeTree(),
+        Select(Ident(nme.command), nme.get)
+      )
+      val run = Apply(Select(Ident(nme.annotation), nme.run), mainCall)
+      val body0 = If(
+        Select(Ident(nme.command), nme.isDefined),
+        Block(argsVal :: args, run),
+        EmptyTree
+      )
+      val body = Block(List(annotVal, infoVal, command), body0) // TODO add `if (cmd.nonEmpty)`
+
       val mainArg = ValDef(nme.args, TypeTree(defn.ArrayType.appliedTo(defn.StringType)), EmptyTree)
         .withFlags(Param)
       /** Replace typed `Ident`s that have been typed with a TypeSplice with the reference to the symbol.

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -852,8 +852,8 @@ class Definitions {
   @tu lazy val XMLTopScopeModule: Symbol = requiredModule("scala.xml.TopScope")
 
   @tu lazy val MainAnnotationClass: ClassSymbol = requiredClass("scala.annotation.MainAnnotation")
-  @tu lazy val MainAnnotationCommandInfo: ClassSymbol = requiredClass("scala.annotation.MainAnnotation.CommandInfo")
-  @tu lazy val MainAnnotationParameterInfo: ClassSymbol = requiredClass("scala.annotation.MainAnnotation.ParameterInfo")
+  @tu lazy val MainAnnotationInfo: ClassSymbol = requiredClass("scala.annotation.MainAnnotation.Info")
+  @tu lazy val MainAnnotationParameter: ClassSymbol = requiredClass("scala.annotation.MainAnnotation.Parameter")
   @tu lazy val MainAnnotationParameterAnnotation: ClassSymbol = requiredClass("scala.annotation.MainAnnotation.ParameterAnnotation")
   @tu lazy val MainAnnotationCommand: ClassSymbol = requiredClass("scala.annotation.MainAnnotation.Command")
 

compiler/src/dotty/tools/dotc/core/StdNames.scala

@@ -543,6 +543,7 @@ object StdNames {
     val ordinalDollar: N        = "$ordinal"
     val ordinalDollar_ : N      = "_$ordinal"
     val origin: N               = "origin"
+    val parameters: N           = "parameters"
     val parts: N                = "parts"
     val postfixOps: N           = "postfixOps"
     val prefix : N              = "prefix"

docs/_docs/reference/experimental/main-annotation.md

@@ -13,33 +13,35 @@ When a users annotates a method with an annotation that extends `MainAnnotation`
  *  @param first Fist number to sum
  *  @param rest The rest of the numbers to sum
  */
-@myMain def sum(first: Int, rest: Int*): Int = first + rest.sum
+@myMain def sum(first: Int, second: Int = 0, rest: Int*): Int = first + second + rest.sum
 ```
 
 ```scala
 object foo {
   def main(args: Array[String]): Unit = {
-
-    val cmd = new myMain().command(
-      info = new CommandInfo(
-        name = "sum",
-        documentation = "Sum all the numbers",
-        parameters = Seq(
-          new ParameterInfo("first", "scala.Int", hasDefault=false, isVarargs=false, "Fist number to sum", Seq()),
-          new ParameterInfo("rest", "scala.Int" , hasDefault=false, isVarargs=true, "The rest of the numbers to sum", Seq())
-        )
-      ),
-      args = args
+    val mainAnnot = new myMain()
+    val info = new Info(
+      name = "foo.main",
+      documentation = "Sum all the numbers",
+      parameters = Seq(
+        new Parameter("first", "scala.Int", hasDefault=false, isVarargs=false, "Fist number to sum", Seq()),
+        new Parameter("second", "scala.Int", hasDefault=true, isVarargs=false, "", Seq()),
+        new Parameter("rest", "scala.Int" , hasDefault=false, isVarargs=true, "The rest of the numbers to sum", Seq())
+      )
     )
-    val args0 = cmd.argGetter[Int](0, None) // using a parser of Int
-    val args1 = cmd.varargGetter[Int] // using a parser of Int
-    cmd.run(() => sum(args0(), args1()*))
+    val mainArgsOpt = mainAnnot.command(info, args)
+    if mainArgsOpt.isDefined then
+      val mainArgs = mainArgsOpt.get
+      val args0 = mainAnnot.argGetter[Int](info.parameters(0), mainArgs(0), None) // using a parser of Int
+      val args1 = mainAnnot.argGetter[Int](info.parameters(1), mainArgs(1), Some(() => sum$default$1())) // using a parser of Int
+      val args2 = mainAnnot.varargGetter[Int](info.parameters(2), mainArgs.drop(2)) // using a parser of Int
+      mainAnnot.run(() => sum(args0(), args1(), args2()*))
   }
 }
 ```
 
-The implementation of the `main` method first instantiates the annotation and then creates a `Command`.
-When creating the `Command`, the arguments can be checked and preprocessed.
+The implementation of the `main` method first instantiates the annotation and then call `command`.
+When calling the `command`, the arguments can be checked and preprocessed.
 Then it defines a series of argument getters calling `argGetter` for each parameter and `varargGetter` for the last one if it is a varargs. `argGetter` gets an optional lambda that computes the default argument.
 Finally, the `run` method is called to run the application. It receives a by-name argument that contains the call the annotated method with the instantiations arguments (using the lambdas from `argGetter`/`varargGetter`).
 
@@ -50,42 +52,46 @@ Example of implementation of `myMain` that takes all arguments positionally. It
 // Parser used to parse command line arguments
 import scala.util.CommandLineParser.FromString[T]
 
-// Result type of the annotated method is Int
-class myMain extends MainAnnotation:
-  import MainAnnotation.{ ParameterInfo, Command }
+// Result type of the annotated method is Int and arguments are parsed using FromString
+@experimental class myMain extends MainAnnotation[FromString, Int]:
+  import MainAnnotation.{ Info, Parameter }
 
-  /** A new command with arguments from `args` */
-  def command(info: CommandInfo, args: Array[String]): Command[FromString, Int] =
+  def command(info: Info, args: Seq[String]): Option[Seq[String]] =
     if args.contains("--help") then
       println(info.documentation)
-      // TODO: Print documentation of the parameters
-      System.exit(0)
-    assert(info.parameters.forall(!_.hasDefault), "Default arguments are not supported")
-    val (plainArgs, varargs) =
-      if info.parameters.last.isVarargs then
-        val numPlainArgs = info.parameters.length - 1
-        assert(numPlainArgs <= args.length, "Not enough arguments")
-        (args.take(numPlainArgs), args.drop(numPlainArgs))
+      None // do not parse or run the program
+    else if info.parameters.exists(_.hasDefault) then
+      println("Default arguments are not supported")
+      None
+    else if info.hasVarargs then
+      val numPlainArgs = info.parameters.length - 1
+      if numPlainArgs <= args.length then
+        println("Not enough arguments")
+        None
+      else
+        Some(args)
+    else
+      if info.parameters.length <= args.length then
+        println("Not enough arguments")
+        None
+      else if info.parameters.length >= args.length then
+        println("Too many arguments")
+        None
       else
-        assert(info.parameters.length <= args.length, "Not enough arguments")
-        assert(info.parameters.length >= args.length, "Too many arguments")
-        (args, Array.empty[String])
-    new MyCommand(plainArgs, varargs)
+        Some(args)
 
-  @experimental
-  class MyCommand(plainArgs: Seq[String], varargs: Seq[String]) extends Command[FromString, Int]:
+  def argGetter[T](param: Parameter, arg: String, defaultArgument: Option[() => T])(using parser: FromString[T]): () => T =
+    () => parser.fromString(arg)
 
-    def argGetter[T](idx: Int, defaultArgument: Option[() => T])(using parser: FromString[T]): () => T =
-      () => parser.fromString(plainArgs(idx))
+  def varargGetter[T](param: Parameter, args: Seq[String])(using parser: FromString[T]): () => Seq[T] =
+    () => args.map(arg => parser.fromString(arg))
 
-    def varargGetter[T](using parser: FromString[T]): () => Seq[T] =
-      () => varargs.map(arg => parser.fromString(arg))
+  def run(program: () => Int): Unit =
+    println("executing program")
 
-    def run(program: () => Int): Unit =
-      println("executing program")
+    try {
       val result = program()
       println("result: " + result)
       println("executed program")
-  end MyCommand
 end myMain
 ```