Merge pull request #748 from dotty-staging/add/non-local/returns

Implement non-local returns

Author: odersky

src/dotty/tools/dotc/Compiler.scala

@@ -48,6 +48,7 @@ class Compiler {
            new ExtensionMethods,
            new ExpandSAMs,
            new TailRec,
+           new LiftTry,
            new ClassOf),
       List(new PatternMatcher,
            new ExplicitOuter,
@@ -68,6 +69,7 @@ class Compiler {
            new LazyVals,
            new Memoize,
            new LinkScala2ImplClasses,
+           new NonLocalReturns,
            new CapturedVars, // capturedVars has a transformUnit: no phases should introduce local mutable vars here
            new Constructors,
            new FunctionalInterfaces,

src/dotty/tools/dotc/ast/tpd.scala

@@ -13,6 +13,7 @@ import config.Printers._
 import typer.Mode
 import collection.mutable
 import typer.ErrorReporting._
+import transform.Erasure
 
 import scala.annotation.tailrec
 
@@ -161,6 +162,10 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
   def Bind(sym: TermSymbol, body: Tree)(implicit ctx: Context): Bind =
     ta.assignType(untpd.Bind(sym.name, body), sym)
 
+  /** A pattern corresponding to `sym: tpe` */
+  def BindTyped(sym: TermSymbol, tpe: Type)(implicit ctx: Context): Bind =
+    Bind(sym, Typed(Underscore(tpe), TypeTree(tpe)))
+
   def Alternative(trees: List[Tree])(implicit ctx: Context): Alternative =
     ta.assignType(untpd.Alternative(trees), trees)
 
@@ -733,9 +738,14 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
       tree.select(defn.Any_asInstanceOf).appliedToType(tp)
     }
 
-    /** `tree.asInstanceOf[tp]` unless tree's type already conforms to `tp` */
+    /** `tree.asInstanceOf[tp]` (or its box/unbox/cast equivalent when after
+     *  erasure and value and non-value types are mixed),
+     *  unless tree's type already conforms to `tp`.
+     */
     def ensureConforms(tp: Type)(implicit ctx: Context): Tree =
-      if (tree.tpe <:< tp) tree else asInstance(tp)
+      if (tree.tpe <:< tp) tree
+      else if (!ctx.erasedTypes) asInstance(tp)
+      else Erasure.Boxing.adaptToType(tree, tp)
 
     /** If inititializer tree is `_', the default value of its type,
      *  otherwise the tree itself.

src/dotty/tools/dotc/core/Contexts.scala

@@ -177,26 +177,25 @@ object Contexts {
     /** The new implicit references that are introduced by this scope */
     private var implicitsCache: ContextualImplicits = null
     def implicits: ContextualImplicits = {
-      if (implicitsCache == null ) {
-        val outerImplicits =
-          if (isImportContext && importInfo.hiddenRoot.exists)
-            outer.implicits exclude importInfo.hiddenRoot
-          else
-            outer.implicits
-        try
-          implicitsCache = {
-            val implicitRefs: List[TermRef] =
-              if (isClassDefContext) owner.thisType.implicitMembers
-              else if (isImportContext) importInfo.importedImplicits
-              else if (isNonEmptyScopeContext) scope.implicitDecls
-              else Nil
-            if (implicitRefs.isEmpty) outerImplicits
-            else new ContextualImplicits(implicitRefs, outerImplicits)(this)
-          }
-        catch {
-          case ex: CyclicReference => implicitsCache = outerImplicits
+      if (implicitsCache == null )
+        implicitsCache = {
+          val implicitRefs: List[TermRef] =
+            if (isClassDefContext)
+              try owner.thisType.implicitMembers
+              catch {
+                case ex: CyclicReference => Nil
+              }
+            else if (isImportContext) importInfo.importedImplicits
+            else if (isNonEmptyScopeContext) scope.implicitDecls
+            else Nil
+          val outerImplicits =
+            if (isImportContext && importInfo.hiddenRoot.exists)
+              outer.implicits exclude importInfo.hiddenRoot
+            else
+              outer.implicits
+          if (implicitRefs.isEmpty) outerImplicits
+          else new ContextualImplicits(implicitRefs, outerImplicits)(this)
         }
-      }
       implicitsCache
     }
 

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

@@ -326,6 +326,7 @@ class Definitions {
     lazy val Product_productArity = ProductClass.requiredMethod(nme.productArity)
     lazy val Product_productPrefix = ProductClass.requiredMethod(nme.productPrefix)
   lazy val LanguageModuleClass          = ctx.requiredModule("dotty.language").moduleClass.asClass
+  lazy val NonLocalReturnControlClass   = ctx.requiredClass("scala.runtime.NonLocalReturnControl")
 
   // Annotation base classes
   lazy val AnnotationClass              = ctx.requiredClass("scala.annotation.Annotation")

src/dotty/tools/dotc/core/SymDenotations.scala

@@ -299,7 +299,11 @@ object SymDenotations {
     /** The expanded name of this denotation. */
     final def expandedName(implicit ctx: Context) =
       if (is(ExpandedName) || isConstructor) name
-      else name.expandedName(initial.asSymDenotation.owner)
+      else {
+        def legalize(name: Name): Name = // JVM method names may not contain `<' or `>' characters
+          if (is(Method)) name.replace('<', '(').replace('>', ')') else name
+        legalize(name.expandedName(initial.asSymDenotation.owner))
+      }
         // need to use initial owner to disambiguate, as multiple private symbols with the same name
         // might have been moved from different origins into the same class
 

src/dotty/tools/dotc/transform/LiftTry.scala

@@ -0,0 +1,66 @@
+package dotty.tools.dotc
+package transform
+
+import TreeTransforms._
+import core.DenotTransformers._
+import core.Symbols._
+import core.Contexts._
+import core.Types._
+import core.Flags._
+import core.Decorators._
+import NonLocalReturns._
+
+/** Lifts try's that might be executed on non-empty expression stacks
+ *  to their own methods. I.e.
+ *
+ *      try body catch handler
+ *
+ *  is lifted to
+ *
+ *      { def liftedTree$n() = try body catch handler; liftedTree$n() }
+ */
+class LiftTry extends MiniPhase with IdentityDenotTransformer { thisTransform =>
+  import ast.tpd._
+
+  /** the following two members override abstract members in Transform */
+  val phaseName: String = "liftTry"
+
+  val treeTransform = new Transform(needLift = false)
+  val liftingTransform = new Transform(needLift = true)
+
+  class Transform(needLift: Boolean) extends TreeTransform {
+    def phase = thisTransform
+
+    override def prepareForApply(tree: Apply)(implicit ctx: Context) =
+      if (tree.fun.symbol.is(Label)) this
+      else liftingTransform
+
+    override def prepareForValDef(tree: ValDef)(implicit ctx: Context) =
+      if (!tree.symbol.exists  ||
+          tree.symbol.isSelfSym ||
+          tree.symbol.owner == ctx.owner.enclosingMethod) this
+      else liftingTransform
+
+    override def prepareForAssign(tree: Assign)(implicit ctx: Context) =
+      if (tree.lhs.symbol.maybeOwner == ctx.owner.enclosingMethod) this
+      else liftingTransform
+
+    override def prepareForReturn(tree: Return)(implicit ctx: Context) =
+      if (!isNonLocalReturn(tree)) this
+      else liftingTransform
+
+    override def prepareForTemplate(tree: Template)(implicit ctx: Context) =
+      treeTransform
+
+    override def transformTry(tree: Try)(implicit ctx: Context, info: TransformerInfo): Tree =
+      if (needLift) {
+        ctx.debuglog(i"lifting tree at ${tree.pos}, current owner = ${ctx.owner}")
+        val fn = ctx.newSymbol(
+          ctx.owner, ctx.freshName("liftedTree").toTermName, Synthetic | Method,
+          MethodType(Nil, tree.tpe), coord = tree.pos)
+        tree.changeOwnerAfter(ctx.owner, fn, thisTransform)
+        Block(DefDef(fn, tree) :: Nil, ref(fn).appliedToNone)
+      }
+      else tree
+  }
+}

src/dotty/tools/dotc/transform/NonLocalReturns.scala

@@ -0,0 +1,92 @@
+package dotty.tools.dotc
+package transform
+
+import core._
+import Contexts._, Symbols._, Types._, Flags._, Decorators._, StdNames._, Constants._, Phases._
+import TreeTransforms._
+import ast.Trees._
+import collection.mutable
+
+object NonLocalReturns {
+  import ast.tpd._
+  def isNonLocalReturn(ret: Return)(implicit ctx: Context) =
+    ret.from.symbol != ctx.owner.enclosingMethod || ctx.owner.is(Lazy)
+}
+
+/** Implement non-local returns using NonLocalReturnControl exceptions.
+ */
+class NonLocalReturns extends MiniPhaseTransform { thisTransformer =>
+  override def phaseName = "nonLocalReturns"
+
+  import NonLocalReturns._
+  import ast.tpd._
+
+  override def runsAfter: Set[Class[_ <: Phase]] = Set(classOf[ElimByName])
+
+  private def ensureConforms(tree: Tree, pt: Type)(implicit ctx: Context) =
+    if (tree.tpe <:< pt) tree
+    else Erasure.Boxing.adaptToType(tree, pt)
+
+  /** The type of a non-local return expression with given argument type */
+  private def nonLocalReturnExceptionType(argtype: Type)(implicit ctx: Context) =
+    defn.NonLocalReturnControlClass.typeRef.appliedTo(argtype)
+
+  /** A hashmap from method symbols to non-local return keys */
+  private val nonLocalReturnKeys = mutable.Map[Symbol, TermSymbol]()
+
+  /** Return non-local return key for given method */
+  private def nonLocalReturnKey(meth: Symbol)(implicit ctx: Context) =
+    nonLocalReturnKeys.getOrElseUpdate(meth,
+      ctx.newSymbol(
+        meth, ctx.freshName("nonLocalReturnKey").toTermName, Synthetic, defn.ObjectType, coord = meth.pos))
+
+  /** Generate a non-local return throw with given return expression from given method.
+   *  I.e. for the method's non-local return key, generate:
+   *
+   *    throw new NonLocalReturnControl(key, expr)
+   *  todo: maybe clone a pre-existing exception instead?
+   *  (but what to do about exceptions that miss their targets?)
+   */
+  private def nonLocalReturnThrow(expr: Tree, meth: Symbol)(implicit ctx: Context) =
+    Throw(
+      New(
+        defn.NonLocalReturnControlClass.typeRef,
+        ref(nonLocalReturnKey(meth)) :: expr.ensureConforms(defn.ObjectType) :: Nil))
+
+  /** Transform (body, key) to:
+   *
+   *  {
+   *    val key = new Object()
+   *    try {
+   *      body
+   *    } catch {
+   *      case ex: NonLocalReturnControl =>
+   *        if (ex.key().eq(key)) ex.value().asInstanceOf[T]
+   *        else throw ex
+   *    }
+   *  }
+   */
+  private def nonLocalReturnTry(body: Tree, key: TermSymbol, meth: Symbol)(implicit ctx: Context) = {
+    val keyDef = ValDef(key, New(defn.ObjectType, Nil))
+    val nonLocalReturnControl = defn.NonLocalReturnControlClass.typeRef
+    val ex = ctx.newSymbol(meth, nme.ex, EmptyFlags, nonLocalReturnControl, coord = body.pos)
+    val pat = BindTyped(ex, nonLocalReturnControl)
+    val rhs = If(
+        ref(ex).select(nme.key).appliedToNone.select(nme.eq).appliedTo(ref(key)),
+        ref(ex).select(nme.value).ensureConforms(meth.info.finalResultType),
+        Throw(ref(ex)))
+    val catches = CaseDef(pat, EmptyTree, rhs) :: Nil
+    val tryCatch = Try(body, catches, EmptyTree)
+    Block(keyDef :: Nil, tryCatch)
+  }
+
+  override def transformDefDef(tree: DefDef)(implicit ctx: Context, info: TransformerInfo): Tree =
+    nonLocalReturnKeys.remove(tree.symbol) match {
+      case Some(key) => cpy.DefDef(tree)(rhs = nonLocalReturnTry(tree.rhs, key, tree.symbol))
+      case _ => tree
+    }
+
+  override def transformReturn(tree: Return)(implicit ctx: Context, info: TransformerInfo): Tree =
+    if (isNonLocalReturn(tree)) nonLocalReturnThrow(tree.expr, tree.from.symbol).withPos(tree.pos)
+    else tree
+}

test/dotc/tests.scala

@@ -115,7 +115,7 @@ class tests extends CompilerTest {
   @Test def neg_zoo = compileFile(negDir, "zoo", xerrors = 12)
 
   val negTailcallDir = negDir + "tailcall/"
-  @Test def neg_tailcall_t1672b = compileFile(negTailcallDir, "t1672b", xerrors = 6)
+  @Test def neg_tailcall_t1672b = compileFile(negTailcallDir, "t1672b", xerrors = 5)
   @Test def neg_tailcall_t3275 = compileFile(negTailcallDir, "t3275", xerrors = 1)
   @Test def neg_tailcall_t6574 = compileFile(negTailcallDir, "t6574", xerrors = 2)
   @Test def neg_tailcall = compileFile(negTailcallDir, "tailrec", xerrors = 7)

tests/pending/run/StackMap.scala renamed to tests/run/StackMap.scala

@@ -0,0 +1,21 @@
+object Test {
+
+  def raise(x: Int) = { throw new Exception(s"$x"); 0 }
+  def handle: Throwable => Int = { case ex: Exception => ex.getMessage().toInt }
+
+  val x = try raise(1) catch handle
+
+  def foo(x: Int) = {
+    val y = try raise(x) catch handle
+    y
+  }
+
+  foo(try 3 catch handle)
+
+  def main(args: Array[String]) = {
+    assert(x == 1)
+    assert(foo(2) == 2)
+    assert(foo(try raise(3) catch handle) == 3)
+  }
+}
+

tests/run/liftedTry.scala

@@ -0,0 +1,32 @@
+object Test {
+
+  def foo(xs: List[Int]): Int = {
+    xs.foreach(x => return x)
+    0
+  }
+
+  def bar(xs: List[Int]): Int = {
+    lazy val y = if (xs.isEmpty) return -1 else xs.head
+    y
+  }
+
+  def baz(x: Int): Int =
+    byName { return -2; 3 }
+
+  def byName(x: => Int): Int = x
+
+  def bam(): Int = { // no non-local return needed here
+    val foo = {
+      return -3
+      3
+    }
+    foo
+  }
+
+  def main(args: Array[String]) = {
+    assert(foo(List(1, 2, 3)) == 1)
+    assert(bar(Nil) == -1)
+    assert(baz(3) == -2)
+    assert(bam() == -3)
+  }
+}