Always fully define the types of lifted expressions

Fixes #822

Author: smarter

src/dotty/tools/dotc/typer/EtaExpansion.scala

@@ -13,6 +13,7 @@ import Decorators._
 import Names._
 import StdNames._
 import Trees._
+import Inferencing._
 import util.Positions._
 import collection.mutable
 
@@ -24,7 +25,8 @@ object EtaExpansion {
     if (isPureExpr(expr)) expr
     else {
       val name = ctx.freshName(prefix).toTermName
-      val sym = ctx.newSymbol(ctx.owner, name, EmptyFlags, expr.tpe.widen, coord = positionCoord(expr.pos))
+      val liftedType = fullyDefinedType(expr.tpe.widen, "expression", expr.pos)
+      val sym = ctx.newSymbol(ctx.owner, name, EmptyFlags, liftedType, coord = positionCoord(expr.pos))
       defs += ValDef(sym, expr)
       ref(sym.valRef)
     }

test/dotc/tests.scala

@@ -53,6 +53,7 @@ class tests extends CompilerTest {
 // This directory doesn't exist anymore
 // @Test def pickle_pickling = compileDir(coreDir, "pickling", testPickling)
   @Test def pickle_ast = compileDir(dotcDir, "ast", testPickling)
+  @Test def pickle_inf = compileFile(posDir, "pickleinf", testPickling)
 
   //@Test def pickle_core = compileDir(dotcDir, "core", testPickling, xerrors = 2) // two spurious comparison errors in Types and TypeOps
 

tests/pos/pickleinf.scala

@@ -0,0 +1,9 @@
+class Bar[N] {
+  def bar(name: N, dummy: Int = 42): N = name
+}
+
+object Test {
+  def test(): Unit = {
+    (new Bar).bar(10)
+  }
+}