Freshen invariant occurrences of caps

Author: Linyxus

compiler/src/dotty/tools/dotc/cc/Capability.scala

@@ -693,7 +693,7 @@ object Capabilities:
     thisMap =>
 
     override def apply(t: Type) =
-      if variance <= 0 then t
+      if variance < 0 then t
       else t match
         case t @ CapturingType(_, _) =>
           mapOver(t)
@@ -703,6 +703,8 @@ object Capabilities:
             this(CapturingType(parent1, ann.tree.toCaptureSet))
           else
             t.derivedAnnotatedType(parent1, ann)
+        case t @ FunctionOrMethod(_, _) if t.isAliasFun =>
+          t  // stop at dependent function types
         case _ =>
           mapFollowingAliases(t)
 

tests/neg-custom-args/captures/boundschecks3.check

@@ -3,15 +3,15 @@
   |           ^
   |           Type argument test.Tree^ does not conform to upper bound test.Tree in inferred type test.C[test.Tree^]
   |
-  |           where:    ^ refers to the universal root capability
+  |           where:    ^ refers to a fresh root capability in the type of value foo
   |
   | longer explanation available when compiling with `-explain`
 -- [E057] Type Mismatch Error: tests/neg-custom-args/captures/boundschecks3.scala:10:11 --------------------------------
 10 |  type T = C[Tree^] // error
    |           ^
    |          Type argument test.Tree^ does not conform to upper bound test.Tree in inferred type test.C[test.Tree^]
    |
-   |          where:    ^ refers to the universal root capability
+   |          where:    ^ refers to a fresh root capability in the type of type T
    |
    | longer explanation available when compiling with `-explain`
 -- [E057] Type Mismatch Error: tests/neg-custom-args/captures/boundschecks3.scala:11:11 --------------------------------

tests/neg-custom-args/captures/box-adapt-cases.check

@@ -1,14 +1,3 @@
--- [E007] Type Mismatch Error: tests/neg-custom-args/captures/box-adapt-cases.scala:8:10 -------------------------------
-8 |  x.value(cap => cap.use())  // error, was OK
-  |          ^^^^^^^^^^^^^^^^
-  |          Found:    (cap: Cap^?) => Int
-  |          Required: Cap^ =>² Int
-  |
-  |          where:    =>  refers to the universal root capability
-  |                    =>² refers to a fresh root capability created in method test1
-  |                    ^   refers to the universal root capability
-  |
-  | longer explanation available when compiling with `-explain`
 -- [E007] Type Mismatch Error: tests/neg-custom-args/captures/box-adapt-cases.scala:15:10 ------------------------------
 15 |  x.value(cap => cap.use())  // error
    |          ^^^^^^^^^^^^^^^^

tests/neg-custom-args/captures/box-adapt-cases.scala

@@ -5,7 +5,7 @@ def test1(): Unit = {
   class Id[X](val value: [T] -> (op: X => T) -> T)
 
   val x: Id[Cap^] = ???
-  x.value(cap => cap.use())  // error, was OK
+  x.value(cap => cap.use())
 }
 
 def test2(io: Cap^): Unit = {

tests/neg-custom-args/captures/class-level-attack.check

@@ -0,0 +1,16 @@
+-- Error: tests/neg-custom-args/captures/class-level-attack.scala:12:24 ------------------------------------------------
+12 |  val r: Ref[IO^] = Ref[IO^](io) // error:
+   |                        ^^^
+   |                        Type variable X of constructor Ref cannot be instantiated to IO^ since
+   |                        that type captures the root capability `cap`.
+   |
+   |                        where:    ^ refers to the universal root capability
+-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/class-level-attack.scala:17:26 ---------------------------
+17 |  def set(x: IO^) = r.put(x)  // error
+   |                          ^
+   |                          Found:    IO^{x}
+   |                          Required: IO^
+   |
+   |                          where:    ^ refers to a fresh root capability in the type of value r
+   |
+   | longer explanation available when compiling with `-explain`

tests/neg-custom-args/captures/class-level-attack.scala

@@ -13,9 +13,8 @@ class C(io: IO^):
     //Type variable X of constructor Ref cannot be instantiated to box IO^ since
     //that type captures the root capability `cap`.
     // where: ^ refers to the universal root capability
-  val r2: Ref[IO^] = Ref(io) // error:
-    //Error: Ref[IO^{io}] does not conform to Ref[IO^] (since Refs are invariant)
-  def set(x: IO^) = r.put(x)
+  val r2: Ref[IO^] = Ref(io)
+  def set(x: IO^) = r.put(x)  // error
 
 def outer(outerio: IO^) =
   val c = C(outerio)

tests/neg-custom-args/captures/i16725.scala

@@ -6,9 +6,9 @@ def usingIO[T](op: IO => T): T = ???
 class Wrapper[T](val value: [R] -> (f: T => R) -> R)
 def mk[T](x: T): Wrapper[T] = Wrapper([R] => f => f(x))
 def useWrappedIO(wrapper: Wrapper[IO]): () -> Unit =
-  () =>
-    wrapper.value: io =>  // error
+  () =>   // error
+    wrapper.value: io =>
       io.brewCoffee()
 def main(): Unit =
-  val escaped = usingIO(io => useWrappedIO(mk(io))) // error
+  val escaped = usingIO(io => useWrappedIO(mk(io)))
   escaped()  // boom