Constraints should not cross phases nor compilation units

Author: liufengyun

compiler/src/dotty/tools/dotc/Run.scala

@@ -202,6 +202,7 @@ class Run(comp: Compiler, ictx: Context) extends ImplicitRunInfo with Constraint
           Stats.trackTime(s"$phase ms ") {
             val start = System.currentTimeMillis
             val profileBefore = profiler.beforePhase(phase)
+            ctx.typerState.constraint = OrderingConstraint.empty
             units = phase.runOn(units)
             profiler.afterPhase(phase, profileBefore)
             if (ctx.settings.Xprint.value.containsPhase(phase))

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

@@ -672,7 +672,6 @@ object TypeOps:
     val childTp = if (child.isTerm) child.termRef else child.typeRef
 
     inContext(ctx.fresh.setExploreTyperState().setFreshGADTBounds) {
-      ctx.typerState.constraint = OrderingConstraint.empty
       instantiateToSubType(childTp, parent).dealias
     }
   }

compiler/src/dotty/tools/dotc/transform/MegaPhase.scala

@@ -456,6 +456,7 @@ class MegaPhase(val miniPhases: Array[MiniPhase]) extends Phase {
     transformTrees(trees, start).asInstanceOf[List[T]]
 
   override def run(using Context): Unit =
+    ctx.typerState.constraint = OrderingConstraint.empty
     ctx.compilationUnit.tpdTree =
       atPhase(miniPhases.last.next)(transformUnit(ctx.compilationUnit.tpdTree))