Address review comments

Author: odersky

Diff for: compiler/src/dotty/tools/dotc/cc/CaptureOps.scala

@@ -269,10 +269,9 @@ extension (tp: Type)
       tp
 
   /** The first element of this path type */
-  final def pathRoot(using Context): Type = tp.dealiasKeepAnnots match
+  final def pathRoot(using Context): Type = tp.dealias match
     case tp1: NamedType if tp1.symbol.owner.isClass => tp1.prefix.pathRoot
-    case ReachCapability(tp1) => tp1.pathRoot
-    case _ => tp
+    case tp1 => tp1
 
   /** If this part starts with `C.this`, the class `C`.
    *  Otherwise, if it starts with a reference `r`, `r`'s owner.

Diff for: compiler/src/dotty/tools/dotc/cc/CaptureSet.scala

@@ -1137,7 +1137,7 @@ object CaptureSet:
             seen += t.symbol
             val upper = t.info.bounds.hi
             if includeTypevars && upper.isExactlyAny then CaptureSet.universal
-            else this(cs, t.info.bounds.hi)
+            else this(cs, upper)
           case t @ FunctionOrMethod(args, res @ Existential(_, _))
           if args.forall(_.isAlwaysPure) =>
             this(cs, Existential.toCap(res))

Diff for: compiler/src/dotty/tools/dotc/cc/CheckCaptures.scala

@@ -380,10 +380,12 @@ class CheckCaptures extends Recheck, SymTransformer:
       // A captured reference with the symbol `sym` is visible from the environment
       // if `sym` is not defined inside the owner of the environment.
       inline def isVisibleFromEnv(sym: Symbol, env: Env) =
-        if env.kind == EnvKind.NestedInOwner then
-          !sym.isProperlyContainedIn(env.owner)
-        else
-          !sym.isContainedIn(env.owner)
+        sym.exists && {
+          if env.kind == EnvKind.NestedInOwner then
+            !sym.isProperlyContainedIn(env.owner)
+          else
+            !sym.isContainedIn(env.owner)
+        }
 
       /** If captureRef `c` refers to a parameter that is not @use declared, report an error.
        *  Exception under deferredReaches: If use comes from a nested closure, accept it.
@@ -450,11 +452,7 @@ class CheckCaptures extends Recheck, SymTransformer:
           // Only captured references that are visible from the environment
           // should be included.
           val included = cs.filter: c =>
-            val isVisible = c.pathRoot match
-              case ref: NamedType => isVisibleFromEnv(ref.symbol.owner, env)
-              case ref: ThisType => isVisibleFromEnv(ref.cls, env)
-              case ref => false
-
+            val isVisible = isVisibleFromEnv(c.pathOwner, env)
             if !isVisible then
               if ccConfig.deferredReaches
               then avoidLocalCapability(c, env, lastEnv)

Diff for: compiler/src/dotty/tools/dotc/printing/RefinedPrinter.scala

@@ -30,7 +30,7 @@ import config.SourceVersion.*
 
 import dotty.tools.dotc.util.SourcePosition
 import dotty.tools.dotc.ast.untpd.{MemberDef, Modifiers, PackageDef, RefTree, Template, TypeDef, ValOrDefDef}
-import cc.{CaptureSet, CapturingType, toCaptureSet, IllegalCaptureRef, isRetains, ReachCapability, MaybeCapability, Existential}
+import cc.*
 import dotty.tools.dotc.parsing.JavaParsers
 
 class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {

Diff for: tests/neg-custom-args/captures/bad-uses-2.scala

@@ -3,4 +3,5 @@ class Test:
   @use def F = ???  // error
   @use val x = ???  // error
   @use type T       // error
-  def foo(@use c: Test): Unit = ??? // OK
+  def foo[@use T](@use c: T): Unit = ??? // OK
+