SI-8046 Only use fast TypeRef#baseTypeSeq with concrete base types

We can only compute the base type sequence (BTS) of a `TypeRef` by
element-wise transforming the BTS of the referenced symbol if
there are no abstract types in its BTS type symbols.

In the now-working test case, `pos/t8046.scala`, the difference
between the old and new calculation of the BTS is:

    this                 = Three.this.Alias[Int]
    sym.info.baseTypeSeq = BTS(One.this.Op[A],Any)
    mapped BTS           = BTS(Three.this.Op[Int],Any)
    full BTS             = BTS(Three.this.Op[Int],Int => Int,Object,Any)

The change to account for PolyType in ArgsTypeRef#transform is now
needed to avoid the full BTS of:

    BTS(Three.this.Op[A],A => A,Object,Any)

Interestingly, everything actually works without that change.

4 files changed, 34 insertions, 1 deletions

diff --git a/test/pending/pos/t8046c.scala b/test/files/pos/t8046c.scala
index 9a8616828d..f05b4c15b5 100644
--- a/test/pending/pos/t8046c.scala
+++ b/test/files/pos/t8046c.scala
@@ -5,7 +5,7 @@ trait One {
 
 trait Three extends One {
   trait Op[A] extends (A => A)
- 
+
   def f1(f: Op[Int])            = f(5)
   def f2(f: Alias[Int])         = f(5)
   def f3[T <: Op[Int]](f: T)    = f(5)
diff --git a/test/files/run/t8046.check b/test/files/run/t8046.check
new file mode 100644
index 0000000000..905b0b35ca
--- /dev/null
+++ b/test/files/run/t8046.check
@@ -0,0 +1,2 @@
+List(trait Op, trait Function1, class Object, class Any)
+BTS(T,Three.this.Op[Int],Int => Int,Object,Any)
diff --git a/test/files/run/t8046/Test.scala b/test/files/run/t8046/Test.scala
new file mode 100644
index 0000000000..f6b525d1b5
--- /dev/null
+++ b/test/files/run/t8046/Test.scala
@@ -0,0 +1,18 @@
+import scala.tools.partest._
+
+object Test extends DirectTest {
+  override def code = ""
+  override def extraSettings: String = "-usejavacp"
+
+  override def show() {
+    val c = newCompiler()
+    new c.Run
+    import c._
+
+    val f4 = typeOf[Three].member(newTermName("f4"))
+    val f4ParamInfo = f4.paramss.head.head.info
+    println(f4ParamInfo.baseClasses)
+    println(f4ParamInfo.baseTypeSeq)
+  }
+}
+
diff --git a/test/files/run/t8046/t8046c.scala b/test/files/run/t8046/t8046c.scala
new file mode 100644
index 0000000000..0b484da530
--- /dev/null
+++ b/test/files/run/t8046/t8046c.scala
@@ -0,0 +1,13 @@
+import language._
+
+trait One {
+  type Op[A]
+  type Alias[A] = Op[A]
+}
+
+trait Three extends One {
+  trait Op[A] extends (A => A)
+
+  def f4[T <: Alias[Int]](f: T) = 0
+}
+