SI-7475 Private members are not inheritable

It turns out `findMembers` has been a bit sloppy in recent
years and has returned private members from *anywhere* up the
base class sequence. Access checks usually pick up the slack
and eliminate the unwanted privates.

But, in concert with the "concrete beats abstract" rule in
`findMember`, the following mishap appeared:

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

    trait T { def a: Int }
    trait B { private def a: Int = 0 }
    trait C extends T with B { a }

    // Exiting paste mode, now interpreting.

    <console>:9: error: method a in trait B cannot be accessed in C
           trait C extends T with B { a }
                                      ^

I noticed this when compiling Akka against JDK 8; a new private method
in the bowels of the JDK was enough to break the build!

It turns out that some finesse in needed to interpret SLS 5.2:

> The private modifier can be used with any definition or declaration
> in a template. They are not inherited by subclasses [...]

So, can we simply exclude privates from all but the first base class?
No, as that might be a refinement class! The following must be
allowed:

    trait A { private def foo = 0; trait T { self: A => this.foo } }

This commit:

  - tracks when the walk up the base class sequence passes the
    first non-refinement class, and excludes private members
  - ... except, if we are at a direct parent of a refinement
    class itself
  - Makes a corresponding change to OverridingPairs, to only consider
    private members if they are owned by the `base` Symbol under
    consideration. We don't need to deal with the subtleties of
    refinements there as that code is only used for bona-fide classes.
  - replaces use of `hasTransOwner` when considering whether a
    private[this] symbol is a member.

The last condition was not grounded in the spec at all. The change
is visible in cases like:

    // Old
    scala> trait A { private[this] val x = 0; class B extends A { this.x } }
    <console>:7: error: value x in trait A cannot be accessed in A.this.B
           trait A { private[this] val x = 0; class B extends A { this.x } }
                                                                       ^
    // New
    scala> trait A { private[this] val x = 0; class B extends A { this.x } }
    <console>:8: error: value x is not a member of A.this.B
           trait A { private[this] val x = 0; class B extends A { this.x } }
                                                                       ^
Furthermore, we no longer give a `private[this]` member a free pass
if it is sourced from the very first base class.

    trait Cake extends Slice {
      private[this] val bippy = ()
    }

    trait Slice { self: Cake =>
      bippy // BCS: Cake, Slice, AnyRef, Any
    }

The different handling between `private` and `private[this]`
still seems a bit dubious.

The spec says:

> An different form of qualification is private[this]. A member M
> marked with this modifier can be accessed only from within the
> object in which it is defined. That is, a selection p.M is only
> legal if the prefix is this or O.this, for some class O enclosing
> the reference. In addition, the restrictions for unqualified
> private apply.

This sounds like a question of access, not membership. If so, we
should admit `private[this]` members from parents of refined types
in `FindMember`.

AFAICT, not too much rests on the distinction: do we get a
"no such member", or "member foo inaccessible" error? I welcome
scrutinee of the checkfile of `neg/t7475f.scala` to help put
this last piece into the puzzle.

One more thing: findMember does not have *any* code the corresponds
to the last sentence of:

> SLS 5.2 The modifier can be qualified with an identifier C
> (e.g. private[C]) that must denote a class or package enclosing
> the definition. Members labeled with such a modifier are accessible
> respectively only from code inside the package C or only from code
> inside the class C and its companion module (§5.4).
> Such members are also inherited only from templates inside C.

When I showed Martin this, he suggested it was an error in the
spec, and we should leave the access checking to callers of
that inherited qualified-private member.

21 files changed, 147 insertions, 47 deletions

diff --git a/test/files/neg/forgot-interpolator.check b/test/files/neg/forgot-interpolator.check
index 157cbb4802..8988458982 100644
--- a/test/files/neg/forgot-interpolator.check
+++ b/test/files/neg/forgot-interpolator.check
@@ -10,9 +10,6 @@ forgot-interpolator.scala:30: warning: `$beppo` looks like an interpolated ident
 forgot-interpolator.scala:34: warning: `$aleppo` looks like an interpolated identifier! Did you forget the interpolator?
     def f = "$aleppo is a pepper and a city."     // warn 4
             ^
-forgot-interpolator.scala:42: warning: `$bar` looks like an interpolated identifier! Did you forget the interpolator?
-    def f = "$bar is private, shall we warn just in case?" // warn 5
-            ^
 forgot-interpolator.scala:47: warning: `$hippo` looks like an interpolated identifier! Did you forget the interpolator?
     def h = "$hippo takes an implicit"  // warn 6
             ^
@@ -26,5 +23,5 @@ forgot-interpolator.scala:90: warning: `$calico` looks like an interpolated iden
     def f4 = "I also salute $calico" // warn 9
              ^
 error: No warnings can be incurred under -Xfatal-warnings.
-9 warnings found
+8 warnings found
 one error found
diff --git a/test/files/neg/forgot-interpolator.scala b/test/files/neg/forgot-interpolator.scala
index 34a7c7aef4..a53054d890 100644
--- a/test/files/neg/forgot-interpolator.scala
+++ b/test/files/neg/forgot-interpolator.scala
@@ -39,7 +39,7 @@ package test {
     if (bar > 8) ???       // use it to avoid extra warning
   }
   class Baz extends Bar {
-    def f = "$bar is private, shall we warn just in case?" // warn 5
+    def f = "$bar is private, shall we warn just in case?" // no longer a warning, private members aren't inherited!
   }
   class G {
     def g = "$greppo takes an arg"  // no warn
diff --git a/test/files/neg/t7475c.check b/test/files/neg/t7475c.check
new file mode 100644
index 0000000000..472808131a
--- /dev/null
+++ b/test/files/neg/t7475c.check
@@ -0,0 +1,7 @@
+t7475c.scala:6: error: value a is not a member of A.this.B
+    println(this.a)     // wait, what?
+                 ^
+t7475c.scala:7: error: value b is not a member of A.this.B
+    println(this.b)     // wait, what?
+                 ^
+two errors found
diff --git a/test/files/neg/t7475c.scala b/test/files/neg/t7475c.scala
new file mode 100644
index 0000000000..cd4a8762ca
--- /dev/null
+++ b/test/files/neg/t7475c.scala
@@ -0,0 +1,9 @@
+class A {
+  private val a: Int = 0
+  private[this] val b: Int = 0
+  class B extends A {
+    def foo(a: A) = a.a // okay
+    println(this.a)     // wait, what?
+    println(this.b)     // wait, what?
+  }
+}
diff --git a/test/files/neg/t7475d.check b/test/files/neg/t7475d.check
new file mode 100644
index 0000000000..6bd1da0d44
--- /dev/null
+++ b/test/files/neg/t7475d.check
@@ -0,0 +1,7 @@
+t7475d.scala:4: error: value priv is not a member of T.this.TT
+  (??? : TT).priv
+             ^
+t7475d.scala:10: error: value priv is not a member of U.this.UU
+  (??? : UU).priv
+             ^
+two errors found
diff --git a/test/files/neg/t7475e.check b/test/files/neg/t7475e.check
new file mode 100644
index 0000000000..48af2be51a
--- /dev/null
+++ b/test/files/neg/t7475e.check
@@ -0,0 +1,4 @@
+t7475e.scala:8: error: value priv is not a member of Base.this.TT
+  (??? : TT).priv
+             ^
+one error found
diff --git a/test/files/neg/t7475e.scala b/test/files/neg/t7475e.scala
new file mode 100644
index 0000000000..e5c4877d6e
--- /dev/null
+++ b/test/files/neg/t7475e.scala
@@ -0,0 +1,12 @@
+trait U {
+}
+
+trait Base {
+  private val priv = 0
+
+  type TT = U with T // should exclude `priv`
+  (??? : TT).priv
+}
+
+trait T extends Base {
+}
diff --git a/test/files/neg/t7475f.check b/test/files/neg/t7475f.check
new file mode 100644
index 0000000000..a07a4480e2
--- /dev/null
+++ b/test/files/neg/t7475f.check
@@ -0,0 +1,10 @@
+t7475f.scala:12: error: method c1 in class C cannot be accessed in C[T]
+  c1 // a member, but inaccessible.
+  ^
+t7475f.scala:13: error: not found: value c2
+  c2 // a member, but inaccessible.
+  ^
+t7475f.scala:26: error: value d2 is not a member of D[Any]
+    other.d2 // not a member
+          ^
+three errors found
diff --git a/test/files/neg/t7475f.scala b/test/files/neg/t7475f.scala
new file mode 100644
index 0000000000..6c5feadf19
--- /dev/null
+++ b/test/files/neg/t7475f.scala
@@ -0,0 +1,28 @@
+class C[T] extends D[T] {
+  private def c1 = 0
+  private[this] def c2 = 0
+}
+
+trait D[T] {
+  self: C[T] =>
+
+  private def d1 = 0
+  private[this] def d2 = 0
+
+  c1 // a member, but inaccessible.
+  c2 // a member, but inaccessible.
+
+  d1 // okay
+  d2 // okay
+
+
+  class C {
+    d1
+    d2
+  }
+
+  def x(other: D[Any]) {
+    other.d1
+    other.d2 // not a member
+  }
+}
diff --git a/test/files/neg/t7507.check b/test/files/neg/t7507.check
index d402869fd4..de30fc7057 100644
--- a/test/files/neg/t7507.check
+++ b/test/files/neg/t7507.check
@@ -1,4 +1,4 @@
-t7507.scala:6: error: value bippy in trait Cake cannot be accessed in Cake
+t7507.scala:6: error: not found: value bippy
   locally(bippy)
           ^
 one error found
diff --git a/test/files/pos/t7475a.scala b/test/files/pos/t7475a.scala
new file mode 100644
index 0000000000..810ce9a05c
--- /dev/null
+++ b/test/files/pos/t7475a.scala
@@ -0,0 +1,11 @@
+trait AbstractPublic {
+  def queue: Any
+}
+trait ConcretePrivate {
+  private val queue: Any = ()
+}
+
+abstract class Mix
+  extends ConcretePrivate with AbstractPublic {
+  final def queue: Any = ()
+}
diff --git a/test/files/pos/t7475b.scala b/test/files/pos/t7475b.scala
new file mode 100644
index 0000000000..a34743b8be
--- /dev/null
+++ b/test/files/pos/t7475b.scala
@@ -0,0 +1,8 @@
+trait U {
+}
+
+trait T {
+  type TT = Any with T with U
+  private val priv = 0
+  (??? : TT).priv
+}
diff --git a/test/files/pos/t7475d.scala b/test/files/pos/t7475d.scala
new file mode 100644
index 0000000000..497c2bf443
--- /dev/null
+++ b/test/files/pos/t7475d.scala
@@ -0,0 +1,11 @@
+trait T {
+  type TT = T with Any
+  private val priv = 0
+  (??? : TT).priv
+}
+
+trait U {
+  type UU = Any with U
+  private val priv = 0
+  (??? : UU).priv
+}
diff --git a/test/files/pos/t7475e.scala b/test/files/pos/t7475e.scala
new file mode 100644
index 0000000000..fbc965c4ca
--- /dev/null
+++ b/test/files/pos/t7475e.scala
@@ -0,0 +1,13 @@
+trait U {
+  private val priv = 0
+  type TT = U with T // should allow `priv`
+  (??? : TT).priv
+}
+
+trait Base {
+
+}
+
+trait T extends Base {
+
+}
diff --git a/test/files/presentation/scope-completion-3.check b/test/files/presentation/scope-completion-3.check
index df3007ab4e..b70a7d5c6b 100644
--- a/test/files/presentation/scope-completion-3.check
+++ b/test/files/presentation/scope-completion-3.check
@@ -3,19 +3,7 @@ reload: Completions.scala
 askScopeCompletion at Completions.scala(75,2)
 ================================================================================
 [response] askScopeCompletion at (75,2)
-retrieved 49 members
-[inaccessible] private class Cb2 extends AnyRef
-[inaccessible] private class Ct2 extends AnyRef
-[inaccessible] private def fb2: Int
-[inaccessible] private def ft2: Int
-[inaccessible] private object Ob2
-[inaccessible] private object Ot2
-[inaccessible] private type tb2 = Completion1.this.tb2
-[inaccessible] private type tt2 = Completion1.this.tt2
-[inaccessible] private[this] val vb2: Int
-[inaccessible] private[this] val vt2: Int
-[inaccessible] private[this] var rb2: Int
-[inaccessible] private[this] var rt2: Int
+retrieved 37 members
 abstract class Base1 extends AnyRef
 abstract trait Trait1 extends AnyRef
 class Cb1 extends AnyRef
@@ -58,19 +46,7 @@ type tt1 = Completion1.this.tt1
 askScopeCompletion at Completions.scala(104,2)
 ================================================================================
 [response] askScopeCompletion at (104,2)
-retrieved 49 members
-[inaccessible] private class Cb2 extends AnyRef
-[inaccessible] private class Ct2 extends AnyRef
-[inaccessible] private def fb2: Int
-[inaccessible] private def ft2: Int
-[inaccessible] private object Ob2
-[inaccessible] private object Ot2
-[inaccessible] private type tb2 = test.Completion2.tb2
-[inaccessible] private type tt2 = test.Completion2.tt2
-[inaccessible] private[this] val vb2: Int
-[inaccessible] private[this] val vt2: Int
-[inaccessible] private[this] var rb2: Int
-[inaccessible] private[this] var rt2: Int
+retrieved 37 members
 abstract class Base1 extends AnyRef
 abstract trait Trait1 extends AnyRef
 class Cb1 extends AnyRef
diff --git a/test/files/presentation/scope-completion-import.check b/test/files/presentation/scope-completion-import.check
index 220ffc399b..50197e5822 100644
--- a/test/files/presentation/scope-completion-import.check
+++ b/test/files/presentation/scope-completion-import.check
@@ -3,10 +3,8 @@ reload: Completions.scala
 askScopeCompletion at Completions.scala(23,4)
 ================================================================================
 [response] askScopeCompletion at (23,4)
-retrieved 18 members
-[inaccessible] private[this] val pVCCC: Int
+retrieved 16 members
 [inaccessible] private[this] val pVOOO: Int
-[inaccessible] private[this] var pRCCC: Int
 [inaccessible] private[this] var pROOO: Int
 class C extends AnyRef
 class Foo extends AnyRef
@@ -27,10 +25,8 @@ val o: test.O.type
 askScopeCompletion at Completions.scala(27,4)
 ================================================================================
 [response] askScopeCompletion at (27,4)
-retrieved 17 members
-[inaccessible] private[this] val pVCCC: Int
+retrieved 15 members
 [inaccessible] private[this] val pVOOO: Int
-[inaccessible] private[this] var pRCCC: Int
 [inaccessible] private[this] var pROOO: Int
 class C extends AnyRef
 class Foo extends AnyRef
@@ -126,10 +122,8 @@ val c: test.C
 askScopeCompletion at Completions.scala(49,4)
 ================================================================================
 [response] askScopeCompletion at (49,4)
-retrieved 18 members
-[inaccessible] private[this] val pVCCC: Int
+retrieved 16 members
 [inaccessible] private[this] val pVOOO: Int
-[inaccessible] private[this] var pRCCC: Int
 [inaccessible] private[this] var pROOO: Int
 class C extends AnyRef
 class Foo extends AnyRef
@@ -150,10 +144,8 @@ private[this] var rOOO: Int
 askScopeCompletion at Completions.scala(59,4)
 ================================================================================
 [response] askScopeCompletion at (59,4)
-retrieved 19 members
-[inaccessible] private[this] val pVCCC: Int
+retrieved 17 members
 [inaccessible] private[this] val pVOOO: Int
-[inaccessible] private[this] var pRCCC: Int
 [inaccessible] private[this] var pROOO: Int
 class C extends AnyRef
 class Foo extends AnyRef
diff --git a/test/files/presentation/visibility.check b/test/files/presentation/visibility.check
index 1ae1213f2d..b77887f8f7 100644
--- a/test/files/presentation/visibility.check
+++ b/test/files/presentation/visibility.check
@@ -79,8 +79,7 @@ protected[package lang] def finalize(): Unit
 askTypeCompletion at Completions.scala(22,11)
 ================================================================================
 [response] askTypeCompletion at (22,11)
-retrieved 35 members
-[inaccessible] private def secretPrivate(): Unit
+retrieved 34 members
 def +(other: String): String
 def ->[B](y: B): (accessibility.AccessibilityChecks, B)
 def ensuring(cond: Boolean): accessibility.AccessibilityChecks
diff --git a/test/files/run/reflection-sorted-members.check b/test/files/run/reflection-sorted-members.check
index c148e19e69..415e073149 100644
--- a/test/files/run/reflection-sorted-members.check
+++ b/test/files/run/reflection-sorted-members.check
@@ -1,4 +1,3 @@
 value a
 value b
 value c
-value x
diff --git a/test/files/run/t7475b.check b/test/files/run/t7475b.check
new file mode 100644
index 0000000000..51993f072d
--- /dev/null
+++ b/test/files/run/t7475b.check
@@ -0,0 +1,2 @@
+2
+2
diff --git a/test/files/run/t7475b.scala b/test/files/run/t7475b.scala
new file mode 100644
index 0000000000..a205602b6d
--- /dev/null
+++ b/test/files/run/t7475b.scala
@@ -0,0 +1,11 @@
+trait A { private val x = 1 }
+trait B { val x = 2 }
+trait C1 extends B with A { println(x) }
+trait C2 extends A with B { println(x) }
+
+object Test {
+  def main(args: Array[String]): Unit = {
+    new C1 { }
+    new C2 { }
+  }
+}
diff --git a/test/files/run/t7507.scala b/test/files/run/t7507.scala
index 6c1959ddac..a5eab6248f 100644
--- a/test/files/run/t7507.scala
+++ b/test/files/run/t7507.scala
@@ -4,6 +4,10 @@ trait Cake extends Slice
 trait Slice { self: Cake =>    // must have self type that extends `Slice`
   private[this] val bippy = () // must be private[this]
   locally(bippy)
+  class C1 {
+    locally(bippy)
+    locally(self.bippy)
+  }
 }
 
 // Originally reported bug: