Be more precise for the inCaptureCheckingOrSetup test

Author: odersky

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

@@ -70,14 +70,17 @@ class CCState:
 
   // ------ Iteration count of capture checking run
 
-  private var iterCount = 1
+  private var iterCount = 0
 
   def iterationId = iterCount
 
   def nextIteration[T](op: => T): T =
     iterCount += 1
     try op finally iterCount -= 1
 
+  def start(): Unit =
+    iterCount = 1
+
   // ------ Global counters -----------------------
 
   /** Next CaptureSet.Var id */

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

@@ -22,11 +22,18 @@ private val Captures: Key[CaptureSet] = Key()
 def isCaptureChecking(using Context): Boolean =
   ctx.phaseId == Phases.checkCapturesPhase.id
 
-/** Are we at checkCaptures or Setup phase? */
+/** Are we in the CheckCaptures or Setup phase? */
 def isCaptureCheckingOrSetup(using Context): Boolean =
-  val ccId = Phases.checkCapturesPhase.id
-  val ctxId = ctx.phaseId
-  ctxId == ccId || ctxId == ccId - 1
+  val ccPhase = Phases.checkCapturesPhase
+  ccPhase.exists
+  && {
+    val ccId = ccPhase.id
+    val ctxId = ctx.phaseId
+    ctxId == ccId
+    || ctxId == ccId - 1 && ccState.iterationId > 0
+      // Note: just checking phase id is not enough since Setup would
+      // also be the phase after pattern matcher.
+  }
 
 /** A dependent function type with given arguments and result type
  *  TODO Move somewhere else where we treat all function type related ops together.

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

@@ -1761,6 +1761,7 @@ class CheckCaptures extends Recheck, SymTransformer:
     private val setup: SetupAPI = thisPhase.prev.asInstanceOf[Setup]
 
     override def checkUnit(unit: CompilationUnit)(using Context): Unit =
+      ccState.start()
       setup.setupUnit(unit.tpdTree, this)
       collectCapturedMutVars.traverse(unit.tpdTree)
 

compiler/src/dotty/tools/dotc/core/TypeComparer.scala

@@ -1010,7 +1010,7 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
           if isCaptureCheckingOrSetup then
             tp1
               .match
-                case tp1: Capability if tp1.isTracked =>
+                case tp1: Capability if isCaptureCheckingOrSetup && tp1.isTracked =>
                   CapturingType(tp1w.stripCapturing, tp1.singletonCaptureSet)
                 case _ =>
                   tp1w
@@ -2110,7 +2110,7 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
    * since `T >: Int` is subsumed by both alternatives in the first match clause.
    *
    * However, the following should not:
-   * 
+   *
    *   def foo[T](e: Expr[T]): T = e match
    *     case I1(_) | B(_) => 42
    *