Merge pull request #14841 from dotty-staging/implement-new-main

Implement new main annotation

Author: nicolasstucki

library/src/scala/annotation/newMain.scala

@@ -0,0 +1,17 @@
+object myProgram:
+
+  /** Adds two numbers */
+  @main def add(num: Int, inc: => Int): Unit =  // error
+    println(s"$num + $inc = ${num + inc}")
+
+end myProgram
+
+object Test:
+  def callMain(args: Array[String]): Unit =
+    val clazz = Class.forName("add")
+    val method = clazz.getMethod("main", classOf[Array[String]])
+    method.invoke(null, args)
+
+  def main(args: Array[String]): Unit =
+    callMain(Array("2", "3"))
+end Test

tests/neg/main-annotation-by-name-param.scala

@@ -0,0 +1,8 @@
+import scala.annotation.newMain
+
+object myProgram:
+
+  @newMain def add(num: Int)(inc: Int): Unit = // error
+    println(s"$num + $inc = ${num + inc}")
+
+end myProgram

tests/neg/main-annotation-currying.scala

@@ -0,0 +1,8 @@
+import scala.annotation.newMain
+
+object myProgram:
+
+  @newMain def nop[T](t: T): T = // error
+    t
+
+end myProgram

tests/neg/main-annotation-generic.scala

@@ -0,0 +1,13 @@
+import scala.annotation.newMain
+
+object myProgram:
+  implicit val x: Int = 2
+  given Int = 3
+
+  @newMain def showImplicit(implicit num: Int): Unit = // error
+    println(num)
+
+  @newMain def showUsing(using num: Int): Unit = // error
+    println(num)
+
+end myProgram

tests/neg/main-annotation-implicit-given.scala

@@ -0,0 +1,8 @@
+import scala.annotation.newMain
+
+object myProgram:
+
+  @newMain @newMain def add1(num: Int, inc: Int): Unit = // error
+    println(s"$num + $inc = ${num + inc}")
+
+end myProgram

tests/neg/main-annotation-multiple-annot.scala

@@ -0,0 +1,11 @@
+import scala.annotation.newMain
+
+object myProgram:
+
+  @newMain val n = 2 // error
+
+  @newMain class A // error
+
+  @newMain val f = ((s: String) => println(s)) // error
+
+end myProgram

tests/neg/main-annotation-nonmethod.scala

@@ -0,0 +1,4 @@
+import scala.annotation.newMain
+
+class A:
+  @newMain def foo(bar: Int) = () // error

tests/neg/main-annotation-nonstatic.scala

@@ -0,0 +1,12 @@
+import scala.annotation.newMain
+
+class MyNumber(val value: Int) {
+  def +(other: MyNumber): MyNumber = MyNumber(value + other.value)
+}
+
+object myProgram:
+
+  @newMain def add(num: MyNumber, inc: MyNumber): Unit = // error
+    println(s"$num + $inc = ${num + inc}")
+
+end myProgram

tests/neg/main-annotation-unknown-parser-1.scala

@@ -0,0 +1,27 @@
+import scala.annotation.newMain
+import scala.util.CommandLineParser.FromString
+
+object myProgram:
+
+  @newMain def add(num: Test.MyNumber, inc: Test.MyNumber): Unit = // error
+    val numV = Test.value(num)
+    val incV = Test.value(inc)
+    println(s"$numV + $incV = ${numV + incV}")
+
+end myProgram
+
+
+object Test:
+  opaque type MyNumber = Int
+
+  def create(n: Int): MyNumber = n
+  def value(n: MyNumber): Int = n
+
+  def callMain(args: Array[String]): Unit =
+    val clazz = Class.forName("add")
+    val method = clazz.getMethod("main", classOf[Array[String]])
+    method.invoke(null, args)
+
+  def main(args: Array[String]): Unit =
+    callMain(Array("2", "3"))
+end Test