Merge pull request scala#1338 from scalamacros/ticket/5418

existentially typed macro expansions now work fine

Author: gkossakowski

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

@@ -710,7 +710,7 @@ trait Macros extends scala.tools.reflect.FastTrack with Traces {
             if (isNullaryInvocation(expandee)) expectedTpe = expectedTpe.finalResultType
             var typechecked = typecheck("macro def return type", expanded, expectedTpe)
             typechecked = typecheck("expected type", typechecked, pt)
-            typechecked updateAttachment MacroExpansionAttachment(expandee)
+            typechecked
           } finally {
             popMacroContext()
           }
@@ -776,7 +776,7 @@ trait Macros extends scala.tools.reflect.FastTrack with Traces {
               macroLogLite("" + expanded.tree + "\n" + showRaw(expanded.tree))
               val freeSyms = expanded.tree.freeTerms ++ expanded.tree.freeTypes
               freeSyms foreach (sym => MacroFreeSymbolError(expandee, sym))
-              Success(atPos(enclosingMacroPosition.focus)(expanded.tree))
+              Success(atPos(enclosingMacroPosition.focus)(expanded.tree updateAttachment MacroExpansionAttachment(expandee)))
             case _ =>
               MacroExpansionIsNotExprError(expandee, expanded)
           }

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

@@ -1197,7 +1197,7 @@ trait Typers extends Modes with Adaptations with Tags {
 
                 val found = tree.tpe
                 if (!found.isErroneous && !pt.isErroneous) {
-                  if (!context.reportErrors && isPastTyper) {
+                  if ((!context.reportErrors && isPastTyper) || tree.attachments.get[MacroExpansionAttachment].isDefined) {
                     val (bound, req) = pt match {
                       case ExistentialType(qs, tpe) => (qs, tpe)
                       case _ => (Nil, pt)
@@ -1230,6 +1230,17 @@ trait Typers extends Modes with Adaptations with Tags {
                       // to consistently transform skolems and fix 6029), I'd like to
                       // investigate ways to avoid skolems completely.
                       //
+                      // upd. The same problem happens when we try to typecheck the result of macro expansion against its expected type
+                      // (which is the return type of the macro definition instantiated in the context of expandee):
+                      //
+                      //   Test.scala:2: error: type mismatch;
+                      //     found   : $u.Expr[Class[_ <: Object]]
+                      //     required: reflect.runtime.universe.Expr[Class[?0(in value <local Test>)]] where type ?0(in value <local Test>) <: Object
+                      //     scala.reflect.runtime.universe.reify(new Object().getClass)
+                      //                                         ^
+                      // Therefore following Martin's advice I use this logic to recover from skolem errors after macro expansions
+                      // (by adding the ` || tree.attachments.get[MacroExpansionAttachment].isDefined` clause to the conditional above).
+                      //
                       log("recovering from existential or skolem type error in tree \n" + tree + "\nwith type " + tree.tpe + "\n expected type = " + pt + "\n context = " + context.tree)
                       return adapt(tree, mode, deriveTypeWithWildcards(boundOrSkolems)(pt))
                     }

test/files/run/t5418a.check

@@ -0,0 +1 @@
+Expr[Class[_ <: java.lang.Object]](new Object().getClass())

test/files/run/t5418a.scala

@@ -0,0 +1,3 @@
+object Test extends App {
+  println(scala.reflect.runtime.universe.reify(new Object().getClass))
+}

test/files/run/t5418b.check

@@ -0,0 +1,2 @@
+new Object().getClass()
+TypeRef(ThisType(java.lang), java.lang.Class, List(TypeRef(NoPrefix, newTypeName("?0"), List())))

test/files/run/t5418b.scala

@@ -0,0 +1,11 @@
+import scala.reflect.runtime.universe._
+import scala.reflect.runtime.{currentMirror => cm}
+import scala.tools.reflect.ToolBox
+
+object Test extends App {
+  val tb = cm.mkToolBox()
+  val untyped = reify(new Object().getClass).tree
+  val typed = tb.typeCheck(untyped)
+  println(typed)
+  println(showRaw(typed.tpe))
+}