Merge pull request #735 from retronym/ticket/4842-2

SI-4842 Forbid access to in-construction this in self-constructor args

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

@@ -222,7 +222,13 @@ trait ContextErrors {
         NormalTypeError(tree, "super constructor cannot be passed a self reference unless parameter is declared by-name")
 
       def SuperConstrArgsThisReferenceError(tree: Tree) =
-        NormalTypeError(tree, "super constructor arguments cannot reference unconstructed `this`")
+        ConstrArgsThisReferenceError("super", tree)
+
+      def SelfConstrArgsThisReferenceError(tree: Tree) =
+        ConstrArgsThisReferenceError("self", tree)
+
+      private def ConstrArgsThisReferenceError(prefix: String, tree: Tree) =
+        NormalTypeError(tree, s"$prefix constructor arguments cannot reference unconstructed `this`")
 
       def TooManyArgumentListsForConstructor(tree: Tree) = {
         issueNormalTypeError(tree, "too many argument lists for constructor invocation")

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

@@ -1846,16 +1846,13 @@ trait Typers extends Modes with Adaptations with Tags {
       val pending = ListBuffer[AbsTypeError]()
       // an object cannot be allowed to pass a reference to itself to a superconstructor
       // because of initialization issues; bug #473
-      for (arg <- superArgs ; tree <- arg) {
-        val sym = tree.symbol
-        if (sym != null && (sym.info.baseClasses contains clazz)) {
-          if (sym.isModule)
-            pending +=  SuperConstrReferenceError(tree)
-          tree match {
-            case This(qual) =>
-              pending += SuperConstrArgsThisReferenceError(tree)
-            case _ => ()
-          }
+      foreachSubTreeBoundTo(superArgs, clazz) { tree =>
+        if (tree.symbol.isModule)
+          pending += SuperConstrReferenceError(tree)
+        tree match {
+          case This(qual) =>
+            pending += SuperConstrArgsThisReferenceError(tree)
+          case _ => ()
         }
       }
 
@@ -1889,7 +1886,39 @@ trait Typers extends Modes with Adaptations with Tags {
       pending.foreach(ErrorUtils.issueTypeError)
     }
 
-    /** Check if a structurally defined method violates implementation restrictions.
+    // Check for SI-4842.
+    private def checkSelfConstructorArgs(ddef: DefDef, clazz: Symbol) {
+      val pending = ListBuffer[AbsTypeError]()
+      ddef.rhs match {
+        case Block(stats, expr) =>
+          val selfConstructorCall = stats.headOption.getOrElse(expr)
+          foreachSubTreeBoundTo(List(selfConstructorCall), clazz) {
+            case tree @ This(qual) =>
+              pending += SelfConstrArgsThisReferenceError(tree)
+            case _ => ()
+          }
+        case _ =>
+      }
+      pending.foreach(ErrorUtils.issueTypeError)
+    }
+
+    /**
+     * Run the provided function for each sub tree of `trees` that
+     * are bound to a symbol with `clazz` as a base class.
+     *
+     * @param f This function can assume that `tree.symbol` is non null
+     */
+    private def foreachSubTreeBoundTo[A](trees: List[Tree], clazz: Symbol)(f: Tree => Unit): Unit =
+      for {
+        tree <- trees
+        subTree <- tree
+      } {
+        val sym = subTree.symbol
+        if (sym != null && sym.info.baseClasses.contains(clazz))
+          f(subTree)
+      }
+
+      /** Check if a structurally defined method violates implementation restrictions.
      *  A method cannot be called if it is a non-private member of a refinement type
      *  and if its parameter's types are any of:
      *    - the self-type of the refinement
@@ -2007,11 +2036,14 @@ trait Typers extends Modes with Adaptations with Tags {
           transformedOrTyped(ddef.rhs, EXPRmode, tpt1.tpe)
         }
 
-        if (meth.isPrimaryConstructor && meth.isClassConstructor && !isPastTyper && !reporter.hasErrors && !meth.owner.isSubClass(AnyValClass)) {
-          // At this point in AnyVal there is no supercall, which will blow up
-          // in computeParamAliases; there's nothing to be computed for Anyval anyway.
+      if (meth.isClassConstructor && !isPastTyper && !reporter.hasErrors && !meth.owner.isSubClass(AnyValClass)) {
+        // At this point in AnyVal there is no supercall, which will blow up
+        // in computeParamAliases; there's nothing to be computed for Anyval anyway.
+        if (meth.isPrimaryConstructor)
           computeParamAliases(meth.owner, vparamss1, rhs1)
-        }
+        else
+          checkSelfConstructorArgs(ddef, meth.owner)
+      }
 
       if (tpt1.tpe.typeSymbol != NothingClass && !context.returnsSeen && rhs1.tpe.typeSymbol != NothingClass)
         rhs1 = checkDead(rhs1)

test/files/neg/t4842a.check

@@ -0,0 +1,4 @@
+t4842a.scala:2: error: self constructor arguments cannot reference unconstructed `this`
+  def this(x: Int) = this(new { println(Foo.this)}) // error
+                                        ^
+one error found

test/files/neg/t4842a.scala

@@ -0,0 +1,3 @@
+class Foo (x: AnyRef) {
+  def this(x: Int) = this(new { println(Foo.this)}) // error
+}

test/files/neg/t4842b.check

@@ -0,0 +1,4 @@
+t4842b.scala:2: error: self constructor arguments cannot reference unconstructed `this`
+  def this() = { this(???)(new { println(TypeArg.this.x) } ); println("next") } // error
+                                         ^
+one error found

test/files/neg/t4842b.scala

@@ -0,0 +1,3 @@
+class TypeArg[X](val x: X)(a: AnyRef) {
+  def this() = { this(???)(new { println(TypeArg.this.x) } ); println("next") } // error
+}

test/files/pos/t4842.scala

@@ -0,0 +1,26 @@
+class Foo (x: AnyRef) {
+  def this() = {
+    this(new { } ) // okay
+  }
+}
+
+
+class Blerg (x: AnyRef) {
+   def this() = {
+     this(new { class Bar { println(Bar.this); new { println(Bar.this) } }; new Bar } ) // okay
+   }
+}
+
+
+class Outer {
+	class Inner (x: AnyRef) {
+	  def this() = {
+	    this(new { class Bar { println(Bar.this); new { println(Bar.this) } }; new Bar } ) // okay
+	  }
+
+	  def this(x: Boolean) = {
+	    this(new { println(Outer.this) } ) // okay
+	  }
+	}
+}
+