Make rejection of deep subtype call stack optional

Move flag that throws exception on deep subtyping stacks from Config varianble to setting.
Disable setting for core-pickling which had a deep subtype failure after pattern matcher
was integrated. Todo: Figure out why the subtype stack got so deep.

3 files changed, 2 insertions, 4 deletions

diff --git a/src/dotty/tools/dotc/config/Config.scala b/src/dotty/tools/dotc/config/Config.scala
index 353ec1dce..b17a5630f 100644
--- a/src/dotty/tools/dotc/config/Config.scala
+++ b/src/dotty/tools/dotc/config/Config.scala
@@ -21,9 +21,6 @@ object Config {
     */
   final val checkNoDoubleBindings = true
 
-  /** Throw an exception if a deep subtype recursion is detected */
-  final val flagDeepSubTypeRecursions = true
-
   /** Show subtype traces for all deep subtype recursions */
   final val traceDeepSubTypeRecursions = false
 
diff --git a/src/dotty/tools/dotc/config/ScalaSettings.scala b/src/dotty/tools/dotc/config/ScalaSettings.scala
index 177813555..f23fb6201 100644
--- a/src/dotty/tools/dotc/config/ScalaSettings.scala
+++ b/src/dotty/tools/dotc/config/ScalaSettings.scala
@@ -146,6 +146,7 @@ class ScalaSettings extends Settings.SettingGroup {
   val YshowSuppressedErrors = BooleanSetting("-Yshow-suppressed-errors", "Also show follow-on errors and warnings that are normally supressed.")
   val Yheartbeat = BooleanSetting("-Yheartbeat", "show heartbeat stack trace of compiler operations.")
   val Yprintpos = BooleanSetting("-Yprintpos", "show tree positions")
+  val YnoDeepSubtypes = BooleanSetting("-YnoDeepSubtypes", "throw an exception on deep subtyping call stacks")
   def stop = YstopAfter
 
   /** Area-specific debug output.
diff --git a/src/dotty/tools/dotc/core/TypeComparer.scala b/src/dotty/tools/dotc/core/TypeComparer.scala
index 805941c5d..5322162d5 100644
--- a/src/dotty/tools/dotc/core/TypeComparer.scala
+++ b/src/dotty/tools/dotc/core/TypeComparer.scala
@@ -422,7 +422,7 @@ class TypeComparer(initctx: Context) extends DotClass {
       pendingSubTypes = new mutable.HashSet[(Type, Type)]
       ctx.log(s"!!! deep subtype recursion involving ${tp1.show} <:< ${tp2.show}, constraint = ${state.constraint.show}")
       ctx.log(s"!!! constraint = ${constraint.show}")
-      assert(!Config.flagDeepSubTypeRecursions)
+      assert(!ctx.settings.YnoDeepSubtypes.value)
       if (Config.traceDeepSubTypeRecursions && !this.isInstanceOf[ExplainingTypeComparer])
         ctx.log(TypeComparer.explained(implicit ctx => ctx.typeComparer.isSubType(tp1, tp2)))
     }