checkNoPrivateLeaks: handle references to companion members

Previously Outer2#Inner#foo failed to compile with:
```
    non-private method foo refers to private value x in its type signature
```

This should compile because the boundary of `foo` is `class Outer2`
and the boundary of `x` is `object Outer2`. This commit fixes this by
also considering the linked boundary in `checkNoPrivateLeaks`.

1 files changed, 17 insertions, 0 deletions

diff --git a/tests/pos/leaks.scala b/tests/pos/leaks.scala
new file mode 100644
index 000000000..dbb47d75a
--- /dev/null
+++ b/tests/pos/leaks.scala
@@ -0,0 +1,17 @@
+class Outer1 {
+  private val x: Int = 1
+
+  private class Inner {
+    def foo: x.type = x // OK
+  }
+}
+
+object Outer2 {
+  private val x: Int = 1
+}
+
+class Outer2 {
+  private class Inner {
+    def foo: Outer2.x.type = Outer2.x // OK
+  }
+}