More uniform treatment of package objects

  - Introduce `Symbol#packageObject` and `Type#packageObject`
    to lookup the member package object of a package class/module,
    and use this far and wide.
  - Replace the overly complicated (and still buggy) implementation
    of `Context#isInPackageObject` with a one liner. The simplifying
    insight is that if we select a symbol from a package prefix
    that does not own that symbol, it *must* have really been
    selected from the package object.
  - Change implicit search to use the cache in
    `ModuleSymbol#implicitMembers` via `Type#implicitMembers`,
    which lets the client code read more naturally.

Fixes a bug with `adapt::insertApply` that Adriaan spotted in a feat
of lateral thinking. This is tested in t8862b.scala. alladin763.scala
adds the test case from the bug originally remedied by `insertApply`
to check we haven't regressed.

1 files changed, 12 insertions, 0 deletions

diff --git a/test/files/pos/t8862b.scala b/test/files/pos/t8862b.scala
new file mode 100644
index 0000000000..8be7fb5fab
--- /dev/null
+++ b/test/files/pos/t8862b.scala
@@ -0,0 +1,12 @@
+package p {
+  trait T[X] { def O : { def apply(): X } }
+  object `package` extends T[Int] {
+    def O: { def apply(): Int } = new { def apply(): Int = 42 }
+  }
+
+  object Test {
+    def main(args: Array[String]): Unit = {
+      val x: Int = O()
+    }
+  }
+}