fix baseType caching during capture checking

- disable caching during Setup
- never cache capturing types

Author: Linyxus

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

@@ -166,6 +166,11 @@ extension (tp: Type)
       case CapturingType(_, _) => true
       case _ => false
 
+  def isEventuallyCapturingType(using Context): Boolean =
+    tp match
+      case EventuallyCapturingType(_, _) => true
+      case _ => false
+
   /** Is type known to be always pure by its class structure,
    *  so that adding a capture set to it would not make sense?
    */

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

@@ -856,8 +856,7 @@ class CheckCaptures extends Recheck, SymTransformer:
         traverseChildren(t)
 
     override def checkUnit(unit: CompilationUnit)(using Context): Unit =
-      Setup(preRecheckPhase, thisPhase, recheckDef)
-        .traverse(ctx.compilationUnit.tpdTree)
+      Setup(preRecheckPhase, thisPhase, recheckDef)(ctx.compilationUnit.tpdTree)
       //println(i"SETUP:\n${Recheck.addRecheckedTypes.transform(ctx.compilationUnit.tpdTree)}")
       withCaptureSetsExplained {
         super.checkUnit(unit)

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

@@ -11,6 +11,7 @@ import ast.tpd
 import transform.Recheck.*
 import CaptureSet.IdentityCaptRefMap
 import Synthetics.isExcluded
+import util.Property
 
 /** A tree traverser that prepares a compilation unit to be capture checked.
  *  It does the following:
@@ -484,4 +485,14 @@ extends tpd.TreeTraverser:
               capt.println(i"update info of ${tree.symbol} from $info to $newInfo")
       case _ =>
   end traverse
+
+  def apply(tree: Tree)(using Context): Unit =
+    traverse(tree)(using ctx.withProperty(Setup.IsDuringSetupKey, Some(())))
 end Setup
+
+object Setup:
+  val IsDuringSetupKey = new Property.Key[Unit]
+
+  def isDuringSetup(using Context): Boolean =
+    ctx.property(IsDuringSetupKey).isDefined
+

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

@@ -24,7 +24,7 @@ import config.Config
 import reporting._
 import collection.mutable
 import transform.TypeUtils._
-import cc.{CapturingType, derivedCapturingType}
+import cc.{CapturingType, derivedCapturingType, Setup, EventuallyCapturingType, isEventuallyCapturingType}
 
 import scala.annotation.internal.sharable
 
@@ -2140,14 +2140,15 @@ object SymDenotations {
     final def baseTypeOf(tp: Type)(using Context): Type = {
       val btrCache = baseTypeCache
       def inCache(tp: Type) = tp match
+        case EventuallyCapturingType(_, _) => false
         case tp: CachedType => btrCache.contains(tp)
         case _ => false
       def record(tp: CachedType, baseTp: Type) = {
         if (Stats.monitored) {
           Stats.record("basetype cache entries")
           if (!baseTp.exists) Stats.record("basetype cache NoTypes")
         }
-        if (!tp.isProvisional)
+        if (!tp.isProvisional && !tp.isEventuallyCapturingType && !Setup.isDuringSetup)
           btrCache(tp) = baseTp
         else
           btrCache.remove(tp) // Remove any potential sentinel value
@@ -2161,8 +2162,9 @@ object SymDenotations {
       def recur(tp: Type): Type = try {
         tp match {
           case tp: CachedType =>
-            val baseTp = btrCache.lookup(tp)
-            if (baseTp != null) return ensureAcyclic(baseTp)
+            val baseTp: Type | Null = btrCache.lookup(tp)
+            if (baseTp != null)
+              return ensureAcyclic(baseTp)
           case _ =>
         }
         if (Stats.monitored) {