SI-9086 Fix regression in implicit search

Implicit search declines to force the info of candidate implicits
that either a) are defined beyond the position of the implicit search
site, or b) enclose the implicit search site.

The second criterion used to prevent consideration of `O` in
the super constructor call:

    implicit object O extends C( { implicitly[X] })

However, after https://github.com/scala/scala/pull/4043, the
block containing the implicit search is typechecked in a context
owned by a local dummy symbol rather than by `O`. (The dummy and
`O` share an owner.)

This led to `O` being considered as a candidate for this implicit
search. This search is undertaken during completion of the info of
`O`, which leads to it being excluded on account of the LOCKED flag.

Unfortunately, this also excludes it from use in implicit search
sites subsequent to `O`, as `ImplicitInfo` caches
`isCyclicOrErroneous`.

This commit adjusts the position of the local dummy to be identical
to that of the object. This serves to exclude `O` as a candidate
during the super call on account of criterion a).

1 files changed, 8 insertions, 0 deletions

diff --git a/test/files/pos/t9086.scala b/test/files/pos/t9086.scala
new file mode 100644
index 0000000000..fba34ee226
--- /dev/null
+++ b/test/files/pos/t9086.scala
@@ -0,0 +1,8 @@
+class X[A](a: A)
+object Test {
+  implicit val ImplicitBoolean: Boolean = true
+  def local = {
+    implicit object X extends X({ implicitly[Boolean] ; "" })
+    implicitly[X[String]] // failed in 2.11.5
+  }
+}