Include capture sets of methods in enclosing class

Author: odersky

compiler/src/dotty/tools/dotc/typer/CheckCaptures.scala

@@ -263,7 +263,12 @@ class CheckCaptures extends Recheck:
             case ref: TermRef => ref.symbol.enclosure != ownEnclosure
             case _ => true
           }
-        checkSubset(targetSet, curEnv.captured, pos)
+        def includeIn(env: Env) =
+          capt.println(i"Include call capture $targetSet in ${env.owner}")
+          checkSubset(targetSet, env.captured, pos)
+        includeIn(curEnv)
+        if curEnv.owner.isTerm && curEnv.outer.owner.isClass then
+          includeIn(curEnv.outer)
 
     def includeBoxedCaptures(tp: Type, pos: SrcPos)(using Context): Unit =
       if curEnv.isOpen then

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

@@ -0,0 +1,7 @@
+-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/nestedclass.scala:15:15 ----------------------------------
+15 |  val xsc: C = xs  // error
+   |               ^^
+   |               Found:    (xs : {cap1} C)
+   |               Required: C
+
+longer explanation available when compiling with `-explain`

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

@@ -0,0 +1,15 @@
+class CC
+type Cap = {*} CC
+
+abstract class C:
+  def head: String
+
+def test(cap1: Cap, cap2: Cap) =
+  def f(x: String): String = if cap1 == cap1 then "" else "a"
+  def g(x: String): String = if cap2 == cap2 then "" else "a"
+
+  val xs =
+    class Cimpl extends C:
+      def head = f("")
+    new Cimpl
+  val xsc: C = xs  // error