More refactoring, avoid globally accessible variable

[Cherry-picked fbe37b8]

Author: odersky

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

@@ -16,7 +16,7 @@ import config.Feature
 import collection.mutable
 import CCState.*
 import reporting.Message
-import CaptureSet.{VarState, CompareResult}
+import CaptureSet.{VarState, CompareResult, CompareFailure}
 
 /** Attachment key for capturing type trees */
 private val Captures: Key[CaptureSet] = Key()
@@ -92,16 +92,13 @@ class CCState:
   def test(op: => CompareResult): CompareResult =
     val saved = notes
     notes = Nil
-    try op.withNotes(notes)
+    try op match
+      case res: CompareFailure => res.withNotes(notes)
+      case res => res
     finally notes = saved
 
   def testOK(op: => Boolean): CompareResult =
-    val saved = notes
-    notes = Nil
-    try
-      if op then CompareResult.OK
-      else CompareResult.Fail(Nil).withNotes(notes)
-    finally notes = saved
+    test(if op then CompareResult.OK else CompareResult.Fail(Nil))
 
   /** Warnings relating to upper approximations of capture sets with
    *  existentially bound variables.

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

@@ -1083,10 +1083,17 @@ object CaptureSet:
    */
   case class ExistentialSubsumesFailure(val ex: root.Result, val other: CaptureRef) extends ErrorNote
 
+  trait CompareFailure:
+    private var myErrorNotes: List[ErrorNote] = Nil
+    def errorNotes: List[ErrorNote] = myErrorNotes
+    def withNotes(notes: List[ErrorNote]): this.type =
+      myErrorNotes = notes
+      this
+
   enum CompareResult extends Showable:
     case OK
-    case Fail(trace: List[CaptureSet])
-    case LevelError(cs: CaptureSet, elem: CaptureRef) extends CompareResult, ErrorNote
+    case Fail(trace: List[CaptureSet]) extends CompareResult, CompareFailure
+    case LevelError(cs: CaptureSet, elem: CaptureRef) extends CompareResult, CompareFailure, ErrorNote
 
     override def toText(printer: Printer): Text =
       inContext(printer.printerContext):
@@ -1111,16 +1118,6 @@ object CaptureSet:
       case result: LevelError => Some(result)
       case _ => None
 
-    private var myErrorNotes: List[ErrorNote] = Nil
-
-    def errorNotes: List[ErrorNote] = myErrorNotes
-
-    def withNotes(notes: List[ErrorNote]): CompareResult = this match
-      case OK => OK
-      case _ =>
-        myErrorNotes = notes
-        this
-
     inline def andAlso(op: Context ?=> CompareResult)(using Context): CompareResult =
       if isOK then op else this
 

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

@@ -18,7 +18,7 @@ import util.{SimpleIdentitySet, EqHashMap, EqHashSet, SrcPos, Property}
 import transform.{Recheck, PreRecheck, CapturedVars}
 import Recheck.*
 import scala.collection.mutable
-import CaptureSet.{withCaptureSetsExplained, IdempotentCaptRefMap, CompareResult, ExistentialSubsumesFailure}
+import CaptureSet.{withCaptureSetsExplained, IdempotentCaptRefMap, CompareResult, CompareFailure, ExistentialSubsumesFailure}
 import CCState.*
 import StdNames.nme
 import NameKinds.{DefaultGetterName, WildcardParamName, UniqueNameKind}
@@ -352,13 +352,15 @@ class CheckCaptures extends Recheck, SymTransformer:
 
     /** If `res` is not CompareResult.OK, report an error */
     def checkOK(res: CompareResult, prefix: => String, added: CaptureRef | CaptureSet, pos: SrcPos, provenance: => String = "")(using Context): Unit =
-      if !res.isOK then
-        inContext(root.printContext(added, res.blocking)):
-          def toAdd: String = errorNotes(res.errorNotes).toAdd.mkString
-          def descr: String =
-            val d = res.blocking.description
-            if d.isEmpty then provenance else ""
-          report.error(em"$prefix included in the allowed capture set ${res.blocking}$descr$toAdd", pos)
+      res match
+        case res: CompareFailure =>
+          inContext(root.printContext(added, res.blocking)):
+            def toAdd: String = errorNotes(res.errorNotes).toAdd.mkString
+            def descr: String =
+              val d = res.blocking.description
+              if d.isEmpty then provenance else ""
+            report.error(em"$prefix included in the allowed capture set ${res.blocking}$descr$toAdd", pos)
+        case _ =>
 
     /** Check subcapturing `{elem} <: cs`, report error on failure */
     def checkElem(elem: CaptureRef, cs: CaptureSet, pos: SrcPos, provenance: => String = "")(using Context) =
@@ -1272,21 +1274,21 @@ class CheckCaptures extends Recheck, SymTransformer:
       if actualBoxed eq actual then
         // Only `addOuterRefs` when there is no box adaptation
         expected1 = addOuterRefs(expected1, actual, tree.srcPos)
-      val result = ccState.testOK(isCompatible(actualBoxed, expected1))
-      if result.isOK then
-        if debugSuccesses then tree match
-            case Ident(_) =>
-              println(i"SUCCESS $tree for $actual <:< $expected:\n${TypeComparer.explained(_.isSubType(actualBoxed, expected1))}")
-            case _ =>
-        actualBoxed
-      else
-        capt.println(i"conforms failed for ${tree}: $actual vs $expected")
-        inContext(root.printContext(actualBoxed, expected1)):
-          err.typeMismatch(tree.withType(actualBoxed), expected1,
-              addApproxAddenda(
-                addenda ++ errorNotes(result.errorNotes),
-                expected1))
-        actual
+      ccState.testOK(isCompatible(actualBoxed, expected1)) match
+        case CompareResult.OK =>
+          if debugSuccesses then tree match
+              case Ident(_) =>
+                println(i"SUCCESS $tree for $actual <:< $expected:\n${TypeComparer.explained(_.isSubType(actualBoxed, expected1))}")
+              case _ =>
+          actualBoxed
+        case fail: CompareFailure =>
+          capt.println(i"conforms failed for ${tree}: $actual vs $expected")
+          inContext(root.printContext(actualBoxed, expected1)):
+            err.typeMismatch(tree.withType(actualBoxed), expected1,
+                addApproxAddenda(
+                  addenda ++ errorNotes(fail.errorNotes),
+                  expected1))
+          actual
     end checkConformsExpr
 
     /** Turn `expected` into a dependent function when `actual` is dependent. */