Add CaptureVar attachment to TypeDef and its rhs

We cannot post-process the typedef in typedTypeDef in the typer,
because adaptation of the rhs prematurely sets the
symbol info to the old bounds pre-expansion, which will
be caught by checkBounds in posttyper.
It is easier to mark the rhs as well and do the expansion in
typedTypeBoundsTree.

Author: bracevac

compiler/src/dotty/tools/dotc/ast/untpd.scala

@@ -533,15 +533,6 @@ object untpd extends Trees.Instance[Untyped] with UntypedTreeInfo {
   def makeCapsOf(tp: RefTree)(using Context): Tree =
     TypeApply(capsInternalDot(nme.capsOf), tp :: Nil)
 
-  // Capture set variable `[C^]` becomes: `[C >: CapSet <: CapSet^{cap}]`
-  def makeCapsBound(refsL: List[Tree] = Nil, refsU: List[Tree] = Nil)(using Context): TypeBoundsTree =
-    val lower = refsL match
-      case Nil => Select(scalaDot(nme.caps), tpnme.CapSet)
-      case refsL => makeRetaining(Select(scalaDot(nme.caps), tpnme.CapSet), refsL, tpnme.retains)
-    val upper =
-      makeRetaining(Select(scalaDot(nme.caps), tpnme.CapSet), refsU, if refsU.isEmpty then tpnme.retainsCap else tpnme.retains)
-    TypeBoundsTree(lower, upper)
-
   def makeConstructor(tparams: List[TypeDef], vparamss: List[List[ValDef]], rhs: Tree = EmptyTree)(using Context): DefDef =
     DefDef(nme.CONSTRUCTOR, joinParams(tparams, vparamss), TypeTree(), rhs)
 

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -3560,12 +3560,15 @@ object Parsers {
             if !isCap && paramOwner.acceptsCtxBounds then typeAndCtxBounds(name)
             else if !isCap && sourceVersion.enablesNewGivens && paramOwner == ParamOwner.Type then typeAndCtxBounds(name)
             else typeBounds()
+          val res = TypeDef(name, lambdaAbstract(hkparams, bounds)).withMods(mods)
           if isCap then
+            res.pushAttachment(CaptureVar, ())
+            // putting the attachment here as well makes post-processing in the typer easier
             bounds.pushAttachment(CaptureVar, ())
             val t = contextBounds(name)
             if t.nonEmpty then
               syntaxError(em"capture parameters cannot have context bounds", t.head.span)
-          TypeDef(name, lambdaAbstract(hkparams, bounds)).withMods(mods)
+          res
         }
       }
       commaSeparated(() => typeParam())
@@ -4114,7 +4117,9 @@ object Parsers {
             tdef.pushAttachment(Backquoted, ())
           if isCapDef then rhs.match
             case ContextBounds(_, _) => syntaxError(em"capture-set member declarations cannot have context bounds", rhs.span)
-            case rhs => rhs.pushAttachment(CaptureVar, ())
+            case rhs => tdef.pushAttachment(CaptureVar, ())
+                        // putting the attachment here as well makes post-processing in the typer easier
+                        rhs.pushAttachment(CaptureVar, ())
           finalizeDef(tdef, mods, start)
         }