Deprecate auto-application of (non-Java-defined) methods with a single empty parameter list

project/GenerateFunctionConverters.scala

@@ -348,7 +348,7 @@ object GenerateFunctionConverters {
 
   def sameText(f: java.io.File, text: String): Boolean = {
     val x = scala.io.Source.fromFile(f)
-    val lines = try { x.getLines.toVector } finally { x.close }
+    val lines = try { x.getLines().toVector } finally { x.close }
     // work around scala/bug#11125
     lines.iterator.filter(_.nonBlank) == Predef.augmentString(text).lines.filter(_.nonBlank)
   }

spec/03-types.md

@@ -685,7 +685,7 @@ An overloaded type consisting of type alternatives $T_1 \commadots T_n (n \geq 2
 
 ###### Example
 ```scala
-def println: Unit
+def println(): Unit
 def println(s: String): Unit = $\ldots$
 def println(x: Float): Unit = $\ldots$
 def println(x: Float, width: Int): Unit = $\ldots$
@@ -694,7 +694,7 @@ def println[A](x: A)(tostring: A => String): Unit = $\ldots$
 define a single function `println` which has an overloaded
 type.
 ```
-println:  => Unit $\overload$
+println:  () Unit $\overload$
           (String) Unit $\overload$
           (Float) Unit $\overload$
           (Float, Int) Unit $\overload$

src/compiler/scala/tools/nsc/typechecker/Typers.scala

@@ -974,27 +974,23 @@ trait Typers extends Adaptations with Tags with TypersTracking with PatternTyper
         }
 
         def matchNullaryLoosely: Boolean = {
-          def test(sym: Symbol) =
-            sym.isJavaDefined ||
-            sym.owner == AnyClass ||
-            sym == Object_clone
+          def test(sym: Symbol) = sym.isJavaDefined || sym.owner == AnyClass
           test(meth) || meth.overrides.exists(test)
         }
-        // (4.2) condition for auto-application by -Xsource level
+
+        // (4.2) condition for auto-application
         //
-        // until 3.0: none (assuming condition for (4.3) was not met)
-        // in 3.0: `meth.isJavaDefined`
-        //         (TODO decide -- currently the condition is more involved to give slack to Scala methods overriding Java-defined ones;
-        //          I think we should resolve that by introducing slack in overriding e.g. a Java-defined `def toString()` by a Scala-defined `def toString`.
-        //          This also works better for dealing with accessors overriding Java-defined methods. The current strategy in methodSig is problematic:
-        //          > // Add a () parameter section if this overrides some method with () parameters
-        //          > val vparamSymssOrEmptyParamsFromOverride =
-        //          This means an accessor that overrides a Java-defined method gets a MethodType instead of a NullaryMethodType, which breaks lots of assumptions about accessors)
+        // Currently the condition is more involved to give slack to Scala methods overriding Java-defined ones;
+        // I (moors) think we should resolve that by introducing slack in overriding e.g. a Java-defined `def toString()` by a Scala-defined `def toString`.
+        // This also works better for dealing with accessors overriding Java-defined methods. The current strategy in methodSig is problematic:
+        // > // Add a () parameter section if this overrides some method with () parameters
+        // > val vparamSymssOrEmptyParamsFromOverride =
+        // This means an accessor that overrides a Java-defined method gets a MethodType instead of a NullaryMethodType, which breaks lots of assumptions about accessors)
         def checkCanAutoApply(): Boolean = {
-          if (sourceLevel3 && !isPastTyper && !matchNullaryLoosely) {
+          if (!isPastTyper && !matchNullaryLoosely) {
             context.deprecationWarning(tree.pos, NoSymbol, s"Auto-application to `()` is deprecated. Supply the empty argument list `()` explicitly to invoke method ${meth.decodedName},\n" +
                                                            s"or remove the empty argument list from its definition (Java-defined methods are exempt).\n"+
-                                                           s"In Scala 3, an unapplied method like this will be eta-expanded into a function.", "3.0.0")
+                                                           s"In Scala 3, an unapplied method like this will be eta-expanded into a function.", "2.13.3")
           }
           true
         }

src/library/scala/collection/Iterator.scala

@@ -40,7 +40,7 @@ import scala.runtime.Statics
   * {{{
   * def f[A](it: Iterator[A]) = {
   *   if (it.hasNext) {            // Safe to reuse "it" after "hasNext"
-  *     it.next                    // Safe to reuse "it" after "next"
+  *     it.next()                  // Safe to reuse "it" after "next"
   *     val remainder = it.drop(2) // it is *not* safe to use "it" again after this line!
   *     remainder.take(2)          // it is *not* safe to use "remainder" after this line!
   *   } else it

src/library/scala/util/control/Exception.scala

@@ -60,7 +60,7 @@ import scala.language.implicitConversions
  *  def printUrl(url: String) : Unit = {
  *    val con = new URL(url) openConnection()
  *    val source = scala.io.Source.fromInputStream(con.getInputStream())
- *    source.getLines.foreach(println)
+ *    source.getLines().foreach(println)
  *  }
  *
  *  val badUrl = "htt/xx"

src/manual/scala/tools/docutil/EmitManPage.scala

@@ -70,9 +70,9 @@ object EmitManPage {
           for (d <- definitions) {
             out println ".TP"
             emitText(d.term)
-            out.println
+            out.println()
             emitText(d.description)
-            if (n > 1) { out.println; n -= 1 }
+            if (n > 1) { out.println(); n -= 1 }
           }
 
         case Link(label, url) =>
@@ -88,7 +88,7 @@ object EmitManPage {
         case TextParagraph(text) =>
           out println ".PP"
           emitText(text)
-          out.println
+          out.println()
 
         case BlockQuote(text) =>
           out println ".TP"

test/benchmarks/src/main/scala/scala/collection/immutable/VectorIterationBenchmark.scala

@@ -31,7 +31,7 @@ class VectorIterationBenchmark {
     var i = 0
     val it = value.iterator
     while (i < size) {
-      bh.consume(it.next)
+      bh.consume(it.next())
       i += 1
     }
   }

test/benchmarks/src/main/scala/scala/collection/mutable/BitSetIteratorBenchmark.scala

@@ -27,7 +27,7 @@ class BitSetIteratorBenchmark {
   @Benchmark def iterateAll(): Unit = {
     var sum = 0
     val it = bs.iterator
-    while (it.hasNext) sum += it.next
+    while (it.hasNext) sum += it.next()
   }
 
 }

test/files/jvm/annotations/Test_2.scala

@@ -120,15 +120,15 @@ object Test4 {
       anns foreach printSourceAnnotation
       if (anns.length > 0) {
         println(target)
-        println
+        println()
       }
     }
     def printParamSourceAnnotations(target: { def getParameterAnnotations(): Array[Array[Annotation]] }): Unit = {
       val anns = target.getParameterAnnotations().flatten
       anns foreach printSourceAnnotation
       if (anns.length > 0) {
         println(target)
-        println
+        println()
       }
     }
     printSourceAnnotations(classOf[Foo1])

test/files/jvm/console.scala

@@ -6,7 +6,7 @@ object Test extends App {
   print(true)
   print(1)
   print(1.0)
-  flush
+  flush()
   println("..")
   println(1)
   printf("Argument nr. %d has value %1.2f\n",

test/files/jvm/future-spec/PromiseTests.scala

@@ -104,7 +104,7 @@ class PromiseTests extends MinimalScalaTest {
     "not be completable with a completed Promise" in {
       {
         val p = Promise[String]().failure(new RuntimeException("unbr0ken"))
-        p.tryCompleteWith(Promise[String].failure(new Exception("br0ken")).future)
+        p.tryCompleteWith(Promise[String]().failure(new Exception("br0ken")).future)
         intercept[RuntimeException] {
           Await.result(p.future, defaultTimeout)
         }.getMessage mustBe ("unbr0ken")

test/files/jvm/scala-concurrent-tck.scala

@@ -117,15 +117,15 @@ class FutureCallbacks extends TestBase {
   }
 
   def testThatNestedCallbacksDoNotYieldStackOverflow(): Unit = {
-    val promise = Promise[Int]
+    val promise = Promise[Int]()
     (0 to 10000).map(Future(_)).foldLeft(promise.future)((pf, f) => f.flatMap(i => pf))
     promise.success(-1)
   }
 
   def stressTestNumberofCallbacks(): Unit = once {
     done =>
-      val promise = Promise[Unit]
-      val otherPromise = Promise[Unit]
+      val promise = Promise[Unit]()
+      val otherPromise = Promise[Unit]()
       def attachMeaninglessCallbacksTo[T](f: Future[T]): Future[T] = {
         (1 to 20000).foreach(_ => f.onComplete(_ => ()))
         f
@@ -359,7 +359,7 @@ def testTransformFailure(): Unit = once {
   def testFlatMapDelayed(): Unit = once {
     done =>
       val f = Future { 5 }
-      val p = Promise[Int]
+      val p = Promise[Int]()
       val g = f flatMap { _ => p.future }
       g onComplete {
         case Success(x) => done(x == 10)

test/files/jvm/serialization.scala

@@ -531,6 +531,6 @@ object Test10_util {
   {
     val random = new Random(345)
     val random2: Random = read(write(random))
-    rep(5) { assert(random.nextInt == random2.nextInt) }
+    rep(5) { assert(random.nextInt() == random2.nextInt()) }
   }
 }

test/files/jvm/throws-annot-from-java.check

@@ -17,7 +17,7 @@ scala> :paste
   	println("atp.typeParams.isEmpty: " + atp.typeParams.isEmpty)
   	println(throwsAnn)
   }
-  println
+  println()
 
   {
   	val method = clazz.info.member(newTermName("bar"))

test/files/jvm/throws-annot-from-java/Test_3.scala

@@ -13,7 +13,7 @@ object Test extends ReplTest {
   	println("atp.typeParams.isEmpty: " + atp.typeParams.isEmpty)
   	println(throwsAnn)
   }
-  println
+  println()
 
   {
   	val method = clazz.info.member(newTermName("bar"))

test/files/jvm/typerep.scala

@@ -49,7 +49,7 @@ object testPrimitives {
   println(getType("abc"))
   println(getType(())) // Unit
   println(getType(classOf[Int])) // Class
-  println
+  println()
 }
 
 object testOptions {
@@ -62,7 +62,7 @@ object testOptions {
   println(getType(None: Option[Int]))
   val y: Option[Int] = None
   println(getType(y))
-  println
+  println()
 }
 
 object testLists {
@@ -71,7 +71,7 @@ object testLists {
   println(getType(List(List(3))))
   println(getType(Nil: List[Int]))
   println(getType(List(1, "abc")))
-  println
+  println()
 }
 
 object testArrays {
@@ -81,7 +81,7 @@ object testArrays {
   println(getType(List(1).toArray))
   println(getType(List[Int]().toArray))
   println(getType(Array(3).drop(1).toArray)) // empty
-  println
+  println()
 }
 
 object testTuples {
@@ -90,7 +90,7 @@ object testTuples {
   println(getType(((3, "abc"), (4, "xyz"))))
   println(getType(((Some('b'), 3), (Some('a'), 4))))
   //println(getType(((Some('b'), 3), (None, 4))))
-  println
+  println()
 }
 
 object testFuncs {
@@ -109,7 +109,7 @@ object testFuncs {
   def f5(f: Int => Int, x: Int) = f(x)
   println(getType(f5 _))
   println(getType(f5(f1, 1)))
-  println
+  println()
 }
 
 class Foo {
@@ -135,12 +135,12 @@ object testClasses {
   val foo2 = new Foo
   println(getType(foo2))
   println(getType(new foo2.Bar(1)))
-  println
+  println()
 
   println(getType(pkg1.c1))
   val c1 = new pkg1.C1
   println(getType(c1))
-  println
+  println()
   */
 }
 

test/files/jvm/unittest_io_Jvm.scala

@@ -8,7 +8,7 @@ object Test {
          |it is split on several lines.
          |
          |isn't it?
-         |""".stripMargin).getLines.toList
+         |""".stripMargin).getLines().toList
     println("lines.size = " + lines.size)
     lines.foreach(println)
   }

test/files/jvm/unreachable/Foo_1.scala

@@ -9,14 +9,14 @@ class Foo_1 {
 
   def unreachableIf: Int = {
     return 42
-    if (util.Random.nextInt % 2 == 0)
+    if (util.Random.nextInt() % 2 == 0)
       0
     else
       1
   }
 
   def unreachableIfBranches: Int = {
-    if (util.Random.nextInt % 2 == 0)
+    if (util.Random.nextInt() % 2 == 0)
       return 42
     else
       return 42
@@ -25,14 +25,14 @@ class Foo_1 {
   }
 
   def unreachableOneLegIf: Int = {
-    if (util.Random.nextInt % 2 == 0)
+    if (util.Random.nextInt() % 2 == 0)
       return 42
 
     return 42
   }
 
   def unreachableLeftBranch: Int = {
-    val result = if (util.Random.nextInt % 2 == 0)
+    val result = if (util.Random.nextInt() % 2 == 0)
       return 42
     else
       42
@@ -41,7 +41,7 @@ class Foo_1 {
   }
 
   def unreachableRightBranch: Int = {
-    val result = if (util.Random.nextInt % 2 == 0)
+    val result = if (util.Random.nextInt() % 2 == 0)
       42
     else
       return 42
@@ -92,7 +92,7 @@ class Foo_1 {
 
   def unreachableSwitch: Int = {
   	return 42
-    val x = util.Random.nextInt % 2
+    val x = util.Random.nextInt() % 2
     x match {
       case 0 => return 0
       case 1 => return 1
@@ -102,7 +102,7 @@ class Foo_1 {
   }
 
   def unreachableAfterSwitch: Int = {
-    val x = util.Random.nextInt % 2
+    val x = util.Random.nextInt() % 2
     x match {
       case 0 => return 42
       case 1 => return 41 + x

test/files/neg/auto-application.check

@@ -1,10 +1,16 @@
-auto-application.scala:2: error: Int does not take parameters
+auto-application.scala:4: error: Int does not take parameters
   ("": Any).##()
               ^
-auto-application.scala:3: error: Int does not take parameters
+auto-application.scala:5: error: Int does not take parameters
   ("": AnyRef).##()
                  ^
-auto-application.scala:4: error: Int does not take parameters
+auto-application.scala:6: error: Int does not take parameters
   ("": Object).##()
                  ^
+auto-application.scala:9: warning: Auto-application to `()` is deprecated. Supply the empty argument list `()` explicitly to invoke method meth,
+or remove the empty argument list from its definition (Java-defined methods are exempt).
+In Scala 3, an unapplied method like this will be eta-expanded into a function.
+  meth // warn, auto-application (of nilary methods) is deprecated
+  ^
+1 warning
 3 errors

test/files/neg/auto-application.scala

@@ -1,5 +1,10 @@
+// scalac: -deprecation -Werror
+
 class Test {
   ("": Any).##()
   ("": AnyRef).##()
   ("": Object).##()
+
+  def meth() = ""
+  meth // warn, auto-application (of nilary methods) is deprecated
 }