SI-8244 Fix raw type regression under separate compilation

In #1901, handling of raw types encountered in signatures during class
file parsing was changed to work in the same manner as
`classExistentialType`, by using
`existentialAbstraction(cls.tparms, cls.tpe_*)`

But this never creates fresh existential symbols, and just sticks
the class type parameters it `quantified`:

	scala> trait T[A <: String]
	defined trait T

	scala> val cls = typeOf[T[_]].typeSymbol
	cls = trait T#101864

	scala> cls.typeParams
	res0 = List(type A#101865)

	scala> cls.tpe_*
	res1 = T#101864[A#101865]

	scala> classExistentialType(cls)
	res3 = T#101864[_ <: String#7209]

	scala> val ExistentialType(quantified, result) = res3
	List(type A#101865)

In the enclosed test case, this class type parameter was substituted
during `typeOf[X] memberType sym`, which led us unsoundly thinking
that `Raw[_]` was `Raw[X]`.

I've added a TODO comment to review the other usages of
`classExistentialType`.

Test variations include joint and separate compilation, and the
corresponding Scala-only code. All fail with type errors now,
as we expect. I've also added a distillation of a bootstrap
error that failed when I forgot to wrap the `existentialType`.

14 files changed, 104 insertions, 5 deletions

diff --git a/src/compiler/scala/tools/nsc/symtab/classfile/ClassfileParser.scala b/src/compiler/scala/tools/nsc/symtab/classfile/ClassfileParser.scala
index 664645e53e..2f9cc01c0b 100644
--- a/src/compiler/scala/tools/nsc/symtab/classfile/ClassfileParser.scala
+++ b/src/compiler/scala/tools/nsc/symtab/classfile/ClassfileParser.scala
@@ -665,8 +665,11 @@ abstract class ClassfileParser {
               // so have to check unsafeTypeParams.isEmpty before worrying about raw type case below,
               // or we'll create a boatload of needless existentials.
               else if (classSym.isMonomorphicType || classSym.unsafeTypeParams.isEmpty) tp
-              // raw type - existentially quantify all type parameters
-              else debuglogResult(s"raw type from $classSym")(unsafeClassExistentialType(classSym))
+              else debuglogResult(s"raw type from $classSym"){
+                // raw type - existentially quantify all type parameters
+                val eparams = typeParamsToExistentials(classSym, classSym.unsafeTypeParams)
+                newExistentialType(eparams, typeRef(pre, classSym, eparams.map(_.tpeHK)))
+              }
             case tp =>
               assert(sig.charAt(index) != '<', s"sig=$sig, index=$index, tp=$tp")
               tp
diff --git a/src/reflect/scala/reflect/internal/Definitions.scala b/src/reflect/scala/reflect/internal/Definitions.scala
index 78e639fdff..645d6aa4ff 100644
--- a/src/reflect/scala/reflect/internal/Definitions.scala
+++ b/src/reflect/scala/reflect/internal/Definitions.scala
@@ -898,12 +898,15 @@ trait Definitions extends api.StandardDefinitions {
      *
      *    C[E1, ..., En] forSome { E1 >: LB1 <: UB1 ... en >: LBn <: UBn }.
      */
+    // TODO Review the way this is used. I see two potential problems:
+    //  1. `existentialAbstraction` here doesn't create fresh existential type symbols, it just
+    //     uses the class type parameter symbols directly as the list of quantified symbols.
+    //     See SI-8244 for the trouble that this can cause.
+    //     Compare with callers of `typeParamsToExistentials` (used in Java raw type handling)
+    //  2. Why don't we require a prefix? Could its omission lead to wrong results in CheckabilityChecker?
     def classExistentialType(clazz: Symbol): Type =
       existentialAbstraction(clazz.typeParams, clazz.tpe_*)
 
-    def unsafeClassExistentialType(clazz: Symbol): Type =
-      existentialAbstraction(clazz.unsafeTypeParams, clazz.tpe_*)
-
     // members of class scala.Any
 
     // TODO these aren't final! They are now overriden in AnyRef/Object. Prior to the fix
diff --git a/test/files/neg/t8244.check b/test/files/neg/t8244.check
new file mode 100644
index 0000000000..90b2bf6f46
--- /dev/null
+++ b/test/files/neg/t8244.check
@@ -0,0 +1,4 @@
+Test_2.scala:9: error: value exxx is not a member of ?0
+    raw.t.exxx // java.lang.ClassCastException: java.lang.String cannot be cast to X
+          ^
+one error found
diff --git a/test/files/neg/t8244/Raw_1.java b/test/files/neg/t8244/Raw_1.java
new file mode 100644
index 0000000000..0c667f1106
--- /dev/null
+++ b/test/files/neg/t8244/Raw_1.java
@@ -0,0 +1,4 @@
+public abstract class Raw_1<T>{
+        public Raw_1 raw() { return new Raw_1<String>() { public String t() { return ""; } }; }
+        public abstract T t();
+}
diff --git a/test/files/neg/t8244/Test_2.scala b/test/files/neg/t8244/Test_2.scala
new file mode 100644
index 0000000000..152bb0b870
--- /dev/null
+++ b/test/files/neg/t8244/Test_2.scala
@@ -0,0 +1,12 @@
+class X extends Raw_1[X] {
+  override def t = this
+  def exxx = 0
+}
+
+object Test extends App {
+  def c(s: X) = {
+    val raw = s.raw
+    raw.t.exxx // java.lang.ClassCastException: java.lang.String cannot be cast to X
+  }
+  c(new X())
+}
diff --git a/test/files/neg/t8244b.check b/test/files/neg/t8244b.check
new file mode 100644
index 0000000000..f6cbf99eb5
--- /dev/null
+++ b/test/files/neg/t8244b.check
@@ -0,0 +1,4 @@
+t8244b.scala:15: error: value exxx is not a member of _$1
+    raw.t.exxx
+          ^
+one error found
diff --git a/test/files/neg/t8244b.scala b/test/files/neg/t8244b.scala
new file mode 100644
index 0000000000..2fb4f451a1
--- /dev/null
+++ b/test/files/neg/t8244b.scala
@@ -0,0 +1,18 @@
+class Raw_1[T]{
+  def raw(): Raw_1[_] = { new Raw_1[String] { def t() = "" } }
+  def t(): T
+}
+
+
+class X extends Raw_1[X] {
+  override def t = this
+  def exxx = 0
+}
+
+object Test extends App {
+  def c(s: X) = {
+    val raw = s.raw
+    raw.t.exxx
+  }
+  c(new X())
+}
diff --git a/test/files/neg/t8244c.check b/test/files/neg/t8244c.check
new file mode 100644
index 0000000000..fd58a5847c
--- /dev/null
+++ b/test/files/neg/t8244c.check
@@ -0,0 +1,4 @@
+t8244c.scala:15: error: value exxx is not a member of _$1
+    raw.t.exxx
+          ^
+one error found
diff --git a/test/files/neg/t8244c.scala b/test/files/neg/t8244c.scala
new file mode 100644
index 0000000000..2fb4f451a1
--- /dev/null
+++ b/test/files/neg/t8244c.scala
@@ -0,0 +1,18 @@
+class Raw_1[T]{
+  def raw(): Raw_1[_] = { new Raw_1[String] { def t() = "" } }
+  def t(): T
+}
+
+
+class X extends Raw_1[X] {
+  override def t = this
+  def exxx = 0
+}
+
+object Test extends App {
+  def c(s: X) = {
+    val raw = s.raw
+    raw.t.exxx
+  }
+  c(new X())
+}
diff --git a/test/files/neg/t8244e.check b/test/files/neg/t8244e.check
new file mode 100644
index 0000000000..ebd74036e5
--- /dev/null
+++ b/test/files/neg/t8244e.check
@@ -0,0 +1,4 @@
+Test.scala:9: error: value exxx is not a member of ?0
+    raw.t.exxx // java.lang.ClassCastException: java.lang.String cannot be cast to X
+          ^
+one error found
diff --git a/test/files/neg/t8244e/Raw.java b/test/files/neg/t8244e/Raw.java
new file mode 100644
index 0000000000..53202e319d
--- /dev/null
+++ b/test/files/neg/t8244e/Raw.java
@@ -0,0 +1,4 @@
+public abstract class Raw<T>{
+        public Raw raw() { return new Raw<String>() { public String t() { return ""; } }; }
+        public abstract T t();
+}
diff --git a/test/files/neg/t8244e/Test.scala b/test/files/neg/t8244e/Test.scala
new file mode 100644
index 0000000000..ca2a90583f
--- /dev/null
+++ b/test/files/neg/t8244e/Test.scala
@@ -0,0 +1,12 @@
+class X extends Raw[X] {
+  override def t = this
+  def exxx = 0
+}
+
+object Test extends App {
+  def c(s: X) = {
+    val raw = s.raw
+    raw.t.exxx // java.lang.ClassCastException: java.lang.String cannot be cast to X
+  }
+  c(new X())
+}
diff --git a/test/files/pos/t8244d/InodeBase_1.java b/test/files/pos/t8244d/InodeBase_1.java
new file mode 100644
index 0000000000..36c2123418
--- /dev/null
+++ b/test/files/pos/t8244d/InodeBase_1.java
@@ -0,0 +1,6 @@
+import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
+
+abstract class INodeBase_1<K, V> {
+    @SuppressWarnings("rawtypes")
+    public static final AtomicReferenceFieldUpdater<INodeBase_1, Object> updater = null;
+}
diff --git a/test/files/pos/t8244d/Test_2.scala b/test/files/pos/t8244d/Test_2.scala
new file mode 100644
index 0000000000..cb39c9692c
--- /dev/null
+++ b/test/files/pos/t8244d/Test_2.scala
@@ -0,0 +1,3 @@
+class INodeX[K, V] extends INodeBase_1[K, V] {
+  INodeBase_1.updater.set(this, null)
+}