Make cap an object instead of a val, change how it is printed

Author: natsukagami

compiler/src/dotty/tools/dotc/printing/PlainPrinter.scala

@@ -195,10 +195,11 @@ class PlainPrinter(_ctx: Context) extends Printer {
     homogenize(tp) match {
       case tp: TypeType =>
         toTextRHS(tp)
+      case tp: TermRef if tp.isCap =>
+        toTextCaptureRef(tp)
       case tp: TermRef
       if !tp.denotationIsCurrent
           && !homogenizedView // always print underlying when testing picklers
-          && !tp.isCap
           || tp.symbol.is(Module)
           || tp.symbol.name == nme.IMPORT =>
         toTextRef(tp) ~ ".type"

library/src/scala/caps/package.scala

@@ -27,16 +27,7 @@ trait Capability extends Any
 
 /** The universal capture reference. */
 @experimental
-val cap: Capability = new Capability() {}
-
-/** The universal capture reference (deprecated) */
-@deprecated("Use `cap` instead")
-@experimental
-val `*`: Capability = cap
-
-@deprecated("Use `Capability` instead")
-@experimental
-type Cap = Capability
+object cap extends Capability
 
 /** Marker trait for classes with methods that requires an exclusive reference. */
 @experimental

tests/neg-custom-args/captures/cc-this2.check

@@ -2,7 +2,7 @@
 -- Error: tests/neg-custom-args/captures/cc-this2/D_2.scala:3:8 --------------------------------------------------------
 3 |  this: D^ => // error
   |        ^^
-  |reference (scala.caps.cap : scala.caps.Capability) captured by this self type is not included in the allowed capture set {} of pure base class class C
+  | reference cap captured by this self type is not included in the allowed capture set {} of pure base class class C
 -- [E058] Type Mismatch Error: tests/neg-custom-args/captures/cc-this2/D_2.scala:2:6 -----------------------------------
 2 |class D extends C: // error
   |      ^

tests/neg-custom-args/captures/exception-definitions.check

@@ -1,7 +1,7 @@
 -- Error: tests/neg-custom-args/captures/exception-definitions.scala:3:8 -----------------------------------------------
 3 |  self: Err^ => // error
   |        ^^^^
-  |reference (scala.caps.cap : scala.caps.Capability) captured by this self type is not included in the allowed capture set {} of pure base class class Throwable
+  |reference cap captured by this self type is not included in the allowed capture set {} of pure base class class Throwable
 -- Error: tests/neg-custom-args/captures/exception-definitions.scala:7:12 ----------------------------------------------
 7 |    val x = c  // error
   |            ^

tests/run-tasty-inspector/stdlibExperimentalDefinitions.scala

@@ -43,9 +43,8 @@ val experimentalDefinitionInLibrary = Set(
   "scala.caps.consume",
   "scala.caps.internal",
   "scala.caps.internal$",
-  "scala.caps.package$package$.*",
-  "scala.caps.package$package$.Cap",
-  "scala.caps.package$package$.cap",
+  "scala.caps.cap",
+  "scala.caps.cap$",
   "scala.caps.unsafe",
   "scala.caps.unsafe$",
   "scala.caps.use",