Fix sorting of accessed this-proxies

They are sorted according to the nesting depth of the classes they
represent. This is no necessarily the same as the nesting level of
the symbols of the proxy classes. i1990a.scala shows an example where
the two differ.

Author: odersky

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

@@ -402,7 +402,12 @@ class Inliner(call: tpd.Tree, rhs: tpd.Tree)(implicit ctx: Context) {
     def outerLevel(selfSym: Symbol): Int = classOf(selfSym).ownersIterator.length
 
     // All needed this-proxies, sorted by nesting depth of the classes they represent (innermost first)
-    val accessedSelfSyms = thisProxy.values.toList.map(_.symbol).sortBy(-outerLevel(_))
+    val accessedSelfSyms =
+      thisProxy.toList.sortBy {
+        case (cls, proxy) => -outerLevel(cls)
+      } map {
+        case (cls, proxy) => proxy.symbol
+      }
 
     // Compute val-definitions for all this-proxies and append them to `bindingsBuf`
     var lastSelf: Symbol = NoSymbol

tests/pos/i1990a.scala

@@ -0,0 +1,20 @@
+class A { self =>
+  class Foo {
+    inline def inlineMeth: Unit = {
+      println(self)
+    }
+  }
+}
+
+class C extends A {
+  class B extends A
+}
+
+object Test {
+  def main(args: Array[String]): Unit = {
+    val c = new C
+    val b = new c.B
+
+    (new b.Foo).inlineMeth
+  }
+}