Make run signature more explicit

Author: nicolasstucki

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

@@ -162,7 +162,7 @@ object MainProxies {
    *         val args0: () => S = cmd.argGetter[S](0, None)
    *         val args1: () => Seq[T] = cmd.varargGetter[T]
    *
-   *         cmd.run(f(args0(), args1()*))
+   *         cmd.run(() => f(args0(), args1()*))
    *       }
    *     }
    */
@@ -352,7 +352,7 @@ object MainProxies {
       None
     else mainFun.info match {
       case _: ExprType =>
-        Some(generateMainClass(ref(mainFun.termRef), Nil, Nil))
+        Some(generateMainClass(unitToValue(ref(mainFun.termRef)), Nil, Nil))
       case mt: MethodType =>
         if (mt.isImplicitMethod)
           report.error(s"main method cannot have implicit parameters", pos)
@@ -362,7 +362,7 @@ object MainProxies {
             report.error(s"main method cannot be curried", pos)
             None
           case _ =>
-            Some(generateMainClass(Apply(ref(mainFun.termRef), argRefs(mt)), argValDefs(mt), parameterInfos(mt)))
+            Some(generateMainClass(unitToValue(Apply(ref(mainFun.termRef), argRefs(mt))), argValDefs(mt), parameterInfos(mt)))
       case _: PolyType =>
         report.error(s"main method cannot have type parameters", pos)
         None

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

@@ -28,7 +28,7 @@ object foo {
     )
     val args0 = cmd.argGetter[Int](0, None) // using cmd.Parser[Int]
     val args1 = cmd.varargGetter[Int] // using cmd.Parser[Int]
-    cmd.run(sum(args0(), args1()*))
+    cmd.run(() => sum(args0(), args1()*))
   }
 }
 ```
@@ -78,9 +78,9 @@ class myMain extends MainAnnotation:
     def varargGetter[T](using parser: Parser[T]): () => Seq[T] =
       () => varargs.map(arg => parser.fromString(arg))
 
-    def run(program: => Result): Unit =
+    def run(program: () => Result): Unit =
       println("executing program")
-      val result = program
+      val result = program()
       println("result: " + result)
       println("executed program")
   end MyCommand

library/src/scala/annotation/MainAnnotation.scala

@@ -80,7 +80,7 @@ object MainAnnotation:
     /** Run `program` if all arguments are valid,
      *  or print usage information and/or error messages.
      */
-    def run(program: => Result): Unit
+    def run(program: () => Result): Unit
   end Command
 
   /** Marker trait for annotations that will be included in the ParameterInfo annotations. */

tests/run/main-annotation-example.scala

@@ -55,9 +55,9 @@ class myMain extends MainAnnotation:
     def varargGetter[T](using parser: Parser[T]): () => Seq[T] =
       () => varargs.map(arg => parser.fromString(arg))
 
-    def run(program: => Result): Unit =
+    def run(program: () => Result): Unit =
       println("executing program")
-      val result = program
+      val result = program()
       println("result: " + result)
       println("executed program")
   end MyCommand

tests/run/main-annotation-homemade-annot-1.scala

@@ -43,5 +43,5 @@ class mainAwait(timeout: Int = 2) extends MainAnnotation:
       override def varargGetter[T](using p: Parser[T]): () => Seq[T] =
         () => for i <- ((parameterInfos.length-1) until args.length) yield p.fromString(args(i))
 
-      override def run(f: => Result): Unit = println(Await.result(f, Duration(timeout, SECONDS)))
+      override def run(f: () => Result): Unit = println(Await.result(f(), Duration(timeout, SECONDS)))
 end mainAwait

tests/run/main-annotation-homemade-annot-2.scala

@@ -43,9 +43,9 @@ class myMain(runs: Int = 3)(after: String*) extends MainAnnotation:
       override def varargGetter[T](using p: Parser[T]): () => Seq[T] =
         () => for i <- (parameterInfos.length until args.length) yield p.fromString(args(i))
 
-      override def run(f: => Result): Unit =
+      override def run(f: () => Result): Unit =
         for (_ <- 1 to runs)
-          f
+          f()
           if after.length > 0 then println(after.mkString(", "))
       end run
   end command

tests/run/main-annotation-homemade-annot-3.scala

@@ -22,5 +22,5 @@ class mainNoArgs extends MainAnnotation:
 
       override def varargGetter[T](using p: Parser[T]): () => Seq[T] = ???
 
-      override def run(f: => Result): Unit = f
+      override def run(program: () => Result): Unit = program()
   end command

tests/run/main-annotation-homemade-annot-4.scala

@@ -22,5 +22,5 @@ class mainManyArgs(i1: Int, s2: String, i3: Int) extends MainAnnotation:
 
       override def varargGetter[T](using p: Parser[T]): () => Seq[T] = ???
 
-      override def run(f: => Result): Unit = f
+      override def run(program: () => Result): Unit = program()
   end command

tests/run/main-annotation-homemade-annot-5.scala

@@ -24,5 +24,5 @@ class mainManyArgs(o: Option[Int]) extends MainAnnotation:
 
       override def varargGetter[T](using p: Parser[T]): () => Seq[T] = ???
 
-      override def run(f: => Result): Unit = f
+      override def run(program: () => Result): Unit = program()
   end command

tests/run/main-annotation-homemade-annot-6.scala

@@ -43,9 +43,9 @@ class myMain extends MainAnnotation:
         println("varargGetter()")
         () => Seq(p.make, p.make)
 
-      override def run(f: => Result): Unit =
+      override def run(f: () => Result): Unit =
         println("run()")
-        f
+        f()
         println()
   end command