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, 3 insertions, 7 deletions

diff --git a/src/reflect/scala/reflect/internal/Symbols.scala b/src/reflect/scala/reflect/internal/Symbols.scala
index 44fce2c9ab..8a2b51bde8 100644
--- a/src/reflect/scala/reflect/internal/Symbols.scala
+++ b/src/reflect/scala/reflect/internal/Symbols.scala
@@ -3357,13 +3357,9 @@ trait Symbols extends api.Symbols { self: SymbolTable =>
     def implicitMembers: Scope = {
       val tp = info
       if ((implicitMembersCacheKey1 ne tp) || (implicitMembersCacheKey2 ne tp.decls.elems)) {
-        // Skip a package object class, because the members are also in
-        // the package and we wish to avoid spurious ambiguities as in pos/t3999.
-        if (!isPackageObjectClass) {
-          implicitMembersCacheValue = tp.implicitMembers
-          implicitMembersCacheKey1 = tp
-          implicitMembersCacheKey2 = tp.decls.elems
-        }
+        implicitMembersCacheValue = tp.implicitMembers
+        implicitMembersCacheKey1 = tp
+        implicitMembersCacheKey2 = tp.decls.elems
       }
       implicitMembersCacheValue
     }