SI-7507 Fix lookup of private[this] member in presence of self type.

In the following code:

	trait Cake extends Slice

	trait Slice { self: Cake =>    // must have self type that extends `Slice`
	  private[this] val bippy = () // must be private[this]
	  locally(bippy)
	}

`ThisType(<Slice>)`.findMember(bippy)` excluded the private local member on
the grounds that the first class in the base type sequence, `Cake`, was
not contained in `Slice`.

	scala> val thisType = typeOf[Slice].typeSymbol.thisType
	thisType: $r.intp.global.Type = Slice.this.type

	scala> thisType.baseClasses
	res6: List[$r.intp.global.Symbol] = List(trait Cake, trait Slice, class Object, class Any)

This commit changes `findMember` to use the symbol of the `ThisType`, rather
than the first base class, as the location of the selection.

src/reflect/scala/reflect/internal/Types.scala

@@ -1172,6 +1172,14 @@ trait Types extends api.Types { self: SymbolTable =>
         continue = false
         val bcs0 = baseClasses
         var bcs = bcs0
+        // omit PRIVATE LOCALS unless selector class is contained in class owning the def.
+        def admitPrivateLocal(owner: Symbol): Boolean = {
+          val selectorClass = this match {
+            case tt: ThisType => tt.sym // SI-7507 the first base class is not necessarily the selector class.
+            case _            => bcs0.head
+          }
+          selectorClass.hasTransOwner(owner)
+        }
         while (!bcs.isEmpty) {
           val decls = bcs.head.info.decls
           var entry = decls.lookupEntry(name)
@@ -1181,10 +1189,10 @@ trait Types extends api.Types { self: SymbolTable =>
             if ((flags & required) == required) {
               val excl = flags & excluded
               if (excl == 0L &&
-                    (// omit PRIVATE LOCALS unless selector class is contained in class owning the def.
+                    (
                   (bcs eq bcs0) ||
                   (flags & PrivateLocal) != PrivateLocal ||
-                  (bcs0.head.hasTransOwner(bcs.head)))) {
+                  admitPrivateLocal(bcs.head))) {
                 if (name.isTypeName || stableOnly && sym.isStable) {
                   if (Statistics.canEnable) Statistics.popTimer(typeOpsStack, start)
                   if (suspension ne null) suspension foreach (_.suspended = false)

test/files/neg/t7507.check

@@ -0,0 +1,4 @@
+t7507.scala:6: error: value bippy in trait Cake cannot be accessed in Cake
+  locally(bippy)
+          ^
+one error found

test/files/neg/t7507.scala

@@ -0,0 +1,7 @@
+trait Cake extends Slice {
+  private[this] val bippy = ()
+}
+
+trait Slice { self: Cake =>
+  locally(bippy)
+}

test/files/run/t7507.scala

@@ -0,0 +1,31 @@
+trait Cake extends Slice
+
+// Minimization
+trait Slice { self: Cake =>    // must have self type that extends `Slice`
+  private[this] val bippy = () // must be private[this]
+  locally(bippy)
+}
+
+// Originally reported bug:
+trait Cake1 extends Slice1
+trait Slice1 { self: Cake1 =>
+  import java.lang.String // any import will do!
+  val Tuple2(x, y) = ((1, 2))
+}
+
+
+// Nesting
+trait Cake3 extends Outer.Slice3
+
+// Minimization
+object Outer {
+  private[this] val bippy = ()
+  trait Slice3 { self: Cake3 =>
+    locally(bippy)
+  }
+}
+
+object Test extends App {
+  val s1 = new Cake1 {}
+  assert((s1.x, s1.y) == (1, 2), (s1.x, s1.y))
+}