Merge pull request #143 from retronym/ticket/prescompiler-nested-async

Avoid spurious "illegal await" error in IDE with nesting

Author: retronym

src/main/scala/scala/async/internal/AsyncAnalysis.scala

@@ -4,6 +4,7 @@
 
 package scala.async.internal
 
+import scala.collection.mutable.ListBuffer
 import scala.reflect.macros.Context
 import scala.collection.mutable
 
@@ -53,14 +54,13 @@ trait AsyncAnalysis {
     }
 
     override def traverse(tree: Tree) {
-      def containsAwait = tree exists isAwait
       tree match {
-        case Try(_, _, _) if containsAwait                    =>
+        case Try(_, _, _) if containsAwait(tree)              =>
           reportUnsupportedAwait(tree, "try/catch")
           super.traverse(tree)
         case Return(_)                                        =>
           c.abort(tree.pos, "return is illegal within a async block")
-        case DefDef(mods, _, _, _, _, _) if mods.hasFlag(Flag.LAZY) && containsAwait =>
+        case DefDef(mods, _, _, _, _, _) if mods.hasFlag(Flag.LAZY) && containsAwait(tree) =>
           reportUnsupportedAwait(tree, "lazy val initializer")
         case CaseDef(_, guard, _) if guard exists isAwait     =>
           // TODO lift this restriction
@@ -74,9 +74,19 @@ trait AsyncAnalysis {
      * @return true, if the tree contained an unsupported await.
      */
     private def reportUnsupportedAwait(tree: Tree, whyUnsupported: String): Boolean = {
-      val badAwaits: List[RefTree] = tree collect {
-        case rt: RefTree if isAwait(rt) => rt
+      val badAwaits = ListBuffer[Tree]()
+      object traverser extends Traverser {
+        override def traverse(tree: Tree): Unit = {
+          if (!isAsync(tree))
+            super.traverse(tree)
+          tree match {
+            case rt: RefTree if isAwait(rt) =>
+              badAwaits += rt
+            case _ =>
+          }
+        }
       }
+      traverser(tree)
       badAwaits foreach {
         tree =>
           reportError(tree.pos, s"await must not be used under a $whyUnsupported.")

src/main/scala/scala/async/internal/AsyncBase.scala

@@ -53,6 +53,11 @@ abstract class AsyncBase {
     c.Expr[futureSystem.Fut[T]](code)
   }
 
+  protected[async] def asyncMethod(u: Universe)(asyncMacroSymbol: u.Symbol): u.Symbol = {
+    import u._
+    asyncMacroSymbol.owner.typeSignature.member(newTermName("async"))
+  }
+
   protected[async] def awaitMethod(u: Universe)(asyncMacroSymbol: u.Symbol): u.Symbol = {
     import u._
     asyncMacroSymbol.owner.typeSignature.member(newTermName("await"))

src/main/scala/scala/async/internal/AsyncMacro.scala

@@ -11,7 +11,7 @@ object AsyncMacro {
       // These members are required by `ExprBuilder`:
       val futureSystem: FutureSystem                             = base.futureSystem
       val futureSystemOps: futureSystem.Ops {val c: self.c.type} = futureSystem.mkOps(c)
-      val containsAwait: c.Tree => Boolean = containsAwaitCached(body0)
+      var containsAwait: c.Tree => Boolean = containsAwaitCached(body0)
     }
   }
 }
@@ -22,7 +22,7 @@ private[async] trait AsyncMacro
 
   val c: scala.reflect.macros.Context
   val body: c.Tree
-  val containsAwait: c.Tree => Boolean
+  var containsAwait: c.Tree => Boolean
 
   lazy val macroPos = c.macroApplication.pos.makeTransparent
   def atMacroPos(t: c.Tree) = c.universe.atPos(macroPos)(t)

src/main/scala/scala/async/internal/AsyncTransform.scala

@@ -26,6 +26,9 @@ trait AsyncTransform {
 
     val anfTree = futureSystemOps.postAnfTransform(anfTree0)
 
+    cleanupContainsAwaitAttachments(anfTree)
+    containsAwait = containsAwaitCached(anfTree)
+
     val applyDefDefDummyBody: DefDef = {
       val applyVParamss = List(List(ValDef(Modifiers(Flag.PARAM), name.tr, TypeTree(futureSystemOps.tryType[Any]), EmptyTree)))
       DefDef(NoMods, name.apply, Nil, applyVParamss, TypeTree(definitions.UnitTpe), literalUnit)

src/main/scala/scala/async/internal/ExprBuilder.scala

@@ -237,10 +237,8 @@ trait ExprBuilder {
     var stateBuilder = new AsyncStateBuilder(startState, symLookup)
     var currState    = startState
 
-    def checkForUnsupportedAwait(tree: Tree) = if (tree exists {
-      case Apply(fun, _) if isAwait(fun) => true
-      case _                             => false
-    }) c.abort(tree.pos, "await must not be used in this position")
+    def checkForUnsupportedAwait(tree: Tree) = if (containsAwait(tree))
+      c.abort(tree.pos, "await must not be used in this position")
 
     def nestedBlockBuilder(nestedTree: Tree, startState: Int, endState: Int) = {
       val (nestedStats, nestedExpr) = statsAndExpr(nestedTree)

src/main/scala/scala/async/internal/TransformUtils.scala

@@ -38,6 +38,9 @@ private[async] trait TransformUtils {
     def fresh(name: String): String = c.freshName(name)
   }
 
+  def isAsync(fun: Tree) =
+    fun.symbol == defn.Async_async
+
   def isAwait(fun: Tree) =
     fun.symbol == defn.Async_await
 
@@ -164,6 +167,7 @@ private[async] trait TransformUtils {
 
     val NonFatalClass = rootMirror.staticModule("scala.util.control.NonFatal")
     val ThrowableClass = rootMirror.staticClass("java.lang.Throwable")
+    val Async_async   = asyncBase.asyncMethod(c.universe)(c.macroApplication.symbol).ensuring(_ != NoSymbol)
     val Async_await   = asyncBase.awaitMethod(c.universe)(c.macroApplication.symbol).ensuring(_ != NoSymbol)
     val IllegalStateExceptionClass = rootMirror.staticClass("java.lang.IllegalStateException")
   }
@@ -281,6 +285,8 @@ private[async] trait TransformUtils {
 
     override def traverse(tree: Tree) {
       tree match {
+        case _ if isAsync(tree) =>
+          // Under -Ymacro-expand:discard, used in the IDE, nested async blocks will be visible to the outer blocks
         case cd: ClassDef          => nestedClass(cd)
         case md: ModuleDef         => nestedModule(md)
         case dd: DefDef            => nestedMethod(dd)
@@ -398,7 +404,7 @@ private[async] trait TransformUtils {
   final def containsAwaitCached(t: Tree): Tree => Boolean = {
     def treeCannotContainAwait(t: Tree) = t match {
       case _: Ident | _: TypeTree | _: Literal => true
-      case _ => false
+      case _ => isAsync(t)
     }
     def shouldAttach(t: Tree) = !treeCannotContainAwait(t)
     val symtab = c.universe.asInstanceOf[scala.reflect.internal.SymbolTable]
@@ -417,11 +423,15 @@ private[async] trait TransformUtils {
       override def traverse(tree: Tree): Unit = {
         stack ::= tree
         try {
-          if (isAwait(tree))
-            stack.foreach(attachContainsAwait)
-          else
-            attachNoAwait(tree)
-          super.traverse(tree)
+          if (isAsync(tree)) {
+            ;
+          } else {
+            if (isAwait(tree))
+              stack.foreach(attachContainsAwait)
+            else
+              attachNoAwait(tree)
+            super.traverse(tree)
+          }
         } finally stack = stack.tail
       }
     }

src/test/scala/scala/async/run/WarningsSpec.scala

@@ -74,4 +74,24 @@ class WarningsSpec {
     run.compileSources(sourceFile :: Nil)
     assert(!global.reporter.hasErrors, global.reporter.asInstanceOf[StoreReporter].infos)
   }
+
+  @Test
+  def ignoreNestedAwaitsInIDE_t1002561() {
+    // https://www.assembla.com/spaces/scala-ide/tickets/1002561
+    val global = mkGlobal("-cp ${toolboxClasspath} -Yrangepos -Ystop-after:typer ")
+    val source = """
+        | class Test {
+        |  def test = {
+        |    import scala.async.Async._, scala.concurrent._, ExecutionContext.Implicits.global
+        |    async {
+        |      1 + await({def foo = (async(await(async(2)))); foo})
+        |    }
+        |  }
+        |}
+      """.stripMargin
+    val run = new global.Run
+    val sourceFile = global.newSourceFile(source)
+    run.compileSources(sourceFile :: Nil)
+    assert(!global.reporter.hasErrors, global.reporter.asInstanceOf[StoreReporter].infos)
+  }
 }