Cleanup Tailrec

Author: allanrenucci

compiler/src/dotty/tools/dotc/config/Printers.scala

@@ -32,6 +32,7 @@ object Printers {
   val plugins: Printer = noPrinter
   val simplify: Printer = noPrinter
   val subtyping: Printer = noPrinter
+  val tailrec: Printer = noPrinter
   val transforms: Printer = noPrinter
   val typr: Printer = noPrinter
   val unapp: Printer = noPrinter

compiler/src/dotty/tools/dotc/reporting/diagnostic/messages.scala

@@ -1801,12 +1801,11 @@ object messages {
   case class TailrecNotApplicable(symbol: Symbol)(implicit ctx: Context)
     extends Message(TailrecNotApplicableID) {
     val kind: String = "Syntax"
-    val symbolKind: String = symbol.showKind
     val msg: String =
       if (symbol.is(Method))
-        hl"TailRec optimisation not applicable, $symbol is neither ${"private"} nor ${"final"}."
+        "TailRec optimisation not applicable, method not tail recursive"
       else
-        hl"TailRec optimisation not applicable, ${symbolKind} isn't a method."
+        hl"TailRec optimisation not applicable, ${symbol.showKind} isn't a method."
     val explanation: String =
       hl"A method annotated ${"@tailrec"} must be declared ${"private"} or ${"final"} so it can't be overridden."
   }

compiler/src/dotty/tools/dotc/transform/TailRec.scala

@@ -1507,8 +1507,8 @@ class ErrorMessagesTests extends ErrorMessagesTest {
       implicit val ctx: Context = ictx
       assertMessageCount(4, messages)
 
-      val tailRegMessages = messages.map({ case m: TailrecNotApplicable => m.symbolKind }).toSet
-      assertEquals(tailRegMessages, Set("variable", "value", "object", "class"))
+      val tailRecMessages = messages.map({ case TailrecNotApplicable(sym) => sym.showKind }).toSet
+      assertEquals(tailRecMessages, Set("variable", "value", "object", "class"))
     }
 
   @Test def notAnExtractor() =

compiler/test/dotty/tools/dotc/reporting/ErrorMessagesTests.scala

@@ -1,5 +1,7 @@
+import annotation.tailrec
+
 object Test1772B {
-  @annotation.tailrec
+  @tailrec
   def bar : Nothing = { // error: TailRec optimisation not applicable
     try {
       throw new RuntimeException
@@ -10,7 +12,7 @@ object Test1772B {
     }
   }
 
-  @annotation.tailrec
+  @tailrec
   def baz : Nothing = { // error: TailRec optimisation not applicable
     try {
       throw new RuntimeException
@@ -21,7 +23,7 @@ object Test1772B {
     }
   }
 
-  @annotation.tailrec
+  @tailrec
   def boz : Nothing = { // error: TailRec optimisation not applicable
     try {
       throw new RuntimeException
@@ -30,7 +32,7 @@ object Test1772B {
     }
   }
 
-  @annotation.tailrec
+  @tailrec
   def bez : Nothing = { // error: TailRec optimisation not applicable
     try {
       bez // error: it is not in tail position
@@ -40,7 +42,7 @@ object Test1772B {
   }
 
   // the `liftedTree` local method will prevent a tail call here.
-  @annotation.tailrec
+  @tailrec
   def bar(i : Int) : Int = { // error: TailRec optimisation not applicable
     if (i == 0) 0
     else 1 + (try {

tests/neg-tailcall/t1672b.check

@@ -1,3 +1,3 @@
 object Test {
-  @annotation.tailrec def foo() = 5                   // error
+  @annotation.tailrec def foo() = 5 // error: not recursive
 }

tests/neg-tailcall/t1672b.scala

@@ -1,10 +1,12 @@
+import annotation.tailrec
+
 class Bad[X, Y](val v: Int) extends AnyVal {
-  @annotation.tailrec final def notTailPos[Z](a: Int)(b: String): Unit = {   // error
-    this.notTailPos[Z](a)(b)          // error
+  @tailrec final def notTailPos[Z](a: Int)(b: String): Unit = { // error: TailRec optimisation not applicable
+    this.notTailPos[Z](a)(b) // error: it is not in tail position
     println("tail")
   }
 
-  @annotation.tailrec final def differentTypeArgs: Unit = {
+  @tailrec final def differentTypeArgs: Unit = {
     {(); new Bad[String, Unit](0)}.differentTypeArgs
   }
 }

tests/neg-tailcall/t3275.check

@@ -1,22 +1,26 @@
+import annotation.tailrec
+
 sealed abstract class Super[+A] {
   def f[B >: A](mem: List[B]) : List[B]
   def g(mem: List[_]) = ???
 }
 // This one should fail, target is a supertype
 class Bop1[+A](val element: A) extends Super[A] {
 
-  @annotation.tailrec final def f[B >: A](mem: List[B]): List[B] = (null: Super[A]).f(mem)
-  @annotation.tailrec final def f1[B >: A](mem: List[B]): List[B] = this.g(mem)
+  @tailrec final def f[B >: A](mem: List[B]): List[B] = // error: TailRec optimisation not applicable
+    (null: Super[A]).f(mem)
+
+  @tailrec final def f1[B >: A](mem: List[B]): List[B] = this.g(mem) // error: TailRec optimisation not applicable
 }
 // These succeed
 class Bop2[+A](val element: A) extends Super[A] {
-  @annotation.tailrec final def f[B >: A](mem: List[B]): List[B] = (null: Bop2[A]).f(mem)
+  @tailrec final def f[B >: A](mem: List[B]): List[B] = (null: Bop2[A]).f(mem)
 }
 object Bop3 extends Super[Nothing] {
-  @annotation.tailrec final def f[B](mem: List[B]): List[B] = (???: Bop3.type).f(mem) // error // error
+  @tailrec final def f[B](mem: List[B]): List[B] = (??? : Bop3.type).f(mem)
 }
 class Bop4[+A](val element: A) extends Super[A] {
-  @annotation.tailrec final def f[B >: A](mem: List[B]): List[B] = Other.f[A].f(mem)
+  @tailrec final def f[B >: A](mem: List[B]): List[B] = Other.f[A].f(mem)
 }
 
 object Other {

tests/neg-tailcall/t3275.scala

@@ -1,14 +1,19 @@
+
 import annotation.tailrec
 
 object Test {
-  @tailrec private def quux(xs: List[String]): List[String] = quux(quux(xs)) // error
+  @tailrec private def quux(xs: List[String]): List[String] =
+    quux(
+      quux(xs) // error: not in tail position
+    )
   @tailrec private def quux2(xs: List[String]): List[String] = xs match {
-    case x1 :: x2 :: rest => quux2(x1 :: quux2(rest))                        // error
-    case _                => Nil
+    case x1 :: x2 :: rest => quux2(
+      x1 :: quux2(rest)) // error: not in tail position
+    case _ => Nil
   }
   @tailrec private def quux3(xs: List[String]): Boolean = xs match {
-    case x :: xs if quux3(List("abc"))  => quux3(xs) // error
-    case _                              => false
+    case x :: xs if quux3(List("abc")) => // error: not in tail position
+      quux3(xs)
+    case _ => false
   }
 }
-

tests/neg-tailcall/t6574.check

@@ -1,6 +1,29 @@
+import annotation.tailrec
+
 object Test4649 {
-  // @annotation.tailrec
+  @tailrec
   def lazyFilter[E](s: Stream[E], p: E => Boolean): Stream[E] = s match {
-    case h #:: t => if (p(h)) h #:: lazyFilter(t, p) else lazyFilter(t, p)
+    case h #:: t =>
+      if (p(h)) h #:: lazyFilter(t, p) // Ok: not a tail call but in a closure
+      else lazyFilter(t, p)
+    case _ =>
+      Stream.empty
+  }
+
+  def cond: Boolean = ???
+  def foo(x: => Int): Int = ???
+
+  @tailrec
+  def bar: Int = {
+    if (cond) foo(bar) // Ok: not a tail call but in a closure
+    else bar
+  }
+
+  def foo2(x: Int => Int) = ???
+
+  @tailrec
+  def bar2: Int = {
+    if (cond) foo2(_ => bar2) // Ok: not a tail call but in a closure
+    else bar2
   }
 }

tests/neg-tailcall/t6574.scala

@@ -1,26 +1,22 @@
+import annotation.tailrec
+
 object O6891 {
   implicit class Foo[A](val value: String) extends AnyVal {
     def bippy() = {
-      @annotation.tailrec def loop(x: A): Unit = loop(x)
+      @tailrec def loop(x: A): Unit = loop(x)
       ()
     }
 
     def boppy() = {
-      @annotation.tailrec def loop(x: value.type): Unit = loop(x)
+      @tailrec def loop(x: value.type): Unit = loop(x)
       ()
     }
 
     def beppy[C](c: => C) = {
       () => c
-      @annotation.tailrec def loop(x: value.type): Unit = loop(x)
+      @tailrec def loop(x: value.type): Unit = loop(x)
         () => c
       ()
     }
   }
-  // uncaught exception during compilation: Types$TypeError("type mismatch;
-  //  found   : A(in method bippy$extension)
-  //  required: A(in class Foo)") @ scala.tools.nsc.typechecker.Contexts$Context.issueCommon(Contexts.scala:396)
-  // error: scala.reflect.internal.Types$TypeError: type mismatch;
-  //  found   : A(in method bippy$extension)
-  //  required: A(in class Foo)
 }