Fix for SI-6206, inconsistency with apply.

The code part of this patch is 100% written by retronym, who
apparently has higher standards than I do because I found it just
lying around in his repository. I think I'll go pick through his
trash and see if he's throwing away any perfectly good muffins.

I made the test case more exciting so as to feel useful.

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

@@ -1044,15 +1044,21 @@ trait Typers extends Modes with Adaptations with Tags {
 
       def insertApply(): Tree = {
         assert(!inHKMode(mode), modeString(mode)) //@M
-        val qual = adaptToName(tree, nme.apply) match {
-          case id @ Ident(_) =>
-            val pre = if (id.symbol.owner.isPackageClass) id.symbol.owner.thisType
-            else if (id.symbol.owner.isClass)
-              context.enclosingSubClassContext(id.symbol.owner).prefix
-            else NoPrefix
-            stabilize(id, pre, EXPRmode | QUALmode, WildcardType)
-          case sel @ Select(qualqual, _) =>
-            stabilize(sel, qualqual.tpe, EXPRmode | QUALmode, WildcardType)
+        val adapted = adaptToName(tree, nme.apply)
+        def stabilize0(pre: Type): Tree = stabilize(adapted, pre, EXPRmode | QUALmode, WildcardType)
+        // TODO reconcile the overlap between Typers#stablize and TreeGen.stabilize
+        val qual = adapted match {
+          case This(_) =>
+            gen.stabilize(adapted)
+          case Ident(_) =>
+            val owner = adapted.symbol.owner
+            val pre =
+              if (owner.isPackageClass) owner.thisType
+              else if (owner.isClass) context.enclosingSubClassContext(owner).prefix
+              else NoPrefix
+            stabilize0(pre)
+          case Select(qualqual, _) =>
+            stabilize0(qualqual.tpe)
           case other =>
             other
         }

test/files/run/t6206.check

@@ -0,0 +1,4 @@
+outer
+outer
+inner
+inner

test/files/run/t6206.scala

@@ -0,0 +1,37 @@
+class Outer {
+  def apply( position : Inner ) {}
+  class Inner
+
+  this.apply(new Inner)
+  this (new Inner) // error,
+}
+
+
+class Outer1 {
+
+  self =>
+
+  def apply( position : Inner ) : String = "outer"
+
+  class Inner( ) {
+
+    def apply(arg: Inner): String = "inner"
+
+    def testMe = {
+      List(
+        self.apply( this ), // a) this works
+        self( this ), // b) this does not work!
+        this apply this,
+        this(this)
+      ) foreach println
+    }
+  }
+}
+
+object Test {
+  def main(args: Array[String]): Unit = {
+    val o = new Outer1
+    val i = new o.Inner
+    i.testMe
+  }
+}