Fix #1990: Handle case where inlining changes class of outer

The new situation in the test was that outer of the inlined method
was `A` but it's as seen from type is a subtype `B`. Outer path logic
can't handle that, so we widen back to an A instance with `baseTypeWithArgs`.

Author: odersky

compiler/src/dotty/tools/dotc/transform/TreeChecker.scala

@@ -12,6 +12,7 @@ import core.Types._
 import core.Flags._
 import core.Constants._
 import core.StdNames._
+import core.NameOps._
 import core.Decorators._
 import core.TypeErasure.isErasedType
 import core.Phases.Phase
@@ -336,7 +337,9 @@ class TreeChecker extends Phase with SymTransformer {
       assert(tree.isTerm || !ctx.isAfterTyper, tree.show + " at " + ctx.phase)
       val tpe = tree.typeOpt
       val sym = tree.symbol
-      if (!tpe.isInstanceOf[WithFixedSym] && sym.exists && !sym.is(Private)) {
+      if (!tpe.isInstanceOf[WithFixedSym] &&
+          sym.exists && !sym.is(Private) && 
+          !tree.name.isOuterSelect // outer selects have effectively fixed symbols) {
         val qualTpe = tree.qualifier.typeOpt
         val member =
           if (sym.is(Private)) qualTpe.member(tree.name)

compiler/src/dotty/tools/dotc/typer/Inliner.scala

@@ -367,6 +367,7 @@ class Inliner(call: tpd.Tree, rhs: tpd.Tree)(implicit ctx: Context) {
       else {
         val proxyName = s"${tpe.cls.name}_this".toTermName
         val proxyType = tpe.asSeenFrom(prefix.tpe, meth.owner)
+          .baseTypeWithArgs(tpe.cls) // outer path logic requires that the proxy has the same class as the original this type 
         thisProxy(tpe.cls) = newSym(proxyName, EmptyFlags, proxyType).termRef
         registerType(meth.owner.thisType) // make sure we have a base from which to outer-select
       }

tests/pos/i1990.scala

@@ -0,0 +1,12 @@
+class A {
+  class Foo {
+    inline def inlineMeth: Unit = {
+      new Bar
+    }
+  }
+  class Bar
+}
+
+class B extends A {
+  (new Foo).inlineMeth
+}