SI-8862 Fix treatment of inherited implicits in package objects

Two spots in implicit search fell prey to a trap with package
objects. Members of a package object are entered into the scope
of the enclosing package, but that doesn't form a suitable prefix
for determing the member type.

A REPL transcript paints a picture that speaks a 1000 words:

```
scala> :paste -raw
// Entering paste mode (ctrl-D to finish)

package p { class C[A] { def foo: A = ??? }; object `package` extends C[String] }

// Exiting paste mode, now interpreting.

scala> val p = rootMirror.getPackageIfDefined("p")
warning: there was one deprecation warning; re-run with -deprecation for details
p: $r.intp.global.Symbol = package p

scala> p.info.decls
res0: $r.intp.global.Scope = Scopes(class C, package object p, method foo)

scala> val foo = p.info.decl(TermName("foo"))
foo: $r.intp.global.Symbol = method foo

scala> p.typeOfThis memberType foo
res1: $r.intp.global.Type = => A

scala> val fooOwner = foo.owner
fooOwner: $r.intp.global.Symbol = class C

scala> p.info.decl(nme.PACKAGE).typeOfThis memberType foo
res3: $r.intp.global.Type = => String
```

This commit detects if we find an implicit in a package module,
and then uses the self type of the corresponding package object
as the prefix for the `ImplicitInfo`. This is done in both
`Context.implicitss` (which collects in-scope implicits), and
in `companionImplicitMap` (which harvests them from the implicit
scope.) In addition, it was necessary / possible to remove a special
case that excluded package object implicits, the referenced tests for
SI-3999 now pass without this.

1 files changed, 5 insertions, 2 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/Implicits.scala b/src/compiler/scala/tools/nsc/typechecker/Implicits.scala
index b85c8e6d42..2fab4557bd 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Implicits.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Implicits.scala
@@ -1012,11 +1012,14 @@ trait Implicits {
               }
             case None =>
               if (pre.isStable && !pre.typeSymbol.isExistentiallyBound) {
-                val companion = companionSymbolOf(sym, context)
+                val companion =
+                  if (sym.isPackageClass) sym.info.member(nme.PACKAGE) //companionSymbolOf(sym.member, context)
+                  else companionSymbolOf(sym, context)
                 companion.moduleClass match {
                   case mc: ModuleClassSymbol =>
+                    val pre1 = if (mc.isPackageObjectClass) mc.typeOfThis else singleType(pre, companion)
                     val infos =
-                      for (im <- mc.implicitMembers.toList) yield new ImplicitInfo(im.name, singleType(pre, companion), im)
+                      for (im <- mc.implicitMembers.toList) yield new ImplicitInfo(im.name, pre1, im)
                     if (infos.nonEmpty)
                       infoMap += (sym -> infos)
                   case _ =>