Refine fix: it suffices to reset constraints for unitCtx

Author: liufengyun

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

@@ -202,7 +202,6 @@ 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/Phases.scala

@@ -300,6 +300,7 @@ object Phases {
     def runOn(units: List[CompilationUnit])(using Context): List[CompilationUnit] =
       units.map { unit =>
         val unitCtx = ctx.fresh.setPhase(this.start).setCompilationUnit(unit).withRootImports
+        unitCtx.typerState.constraint = OrderingConstraint.empty
         run(using unitCtx)
         unitCtx.compilationUnit
       }

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

@@ -456,7 +456,6 @@ 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))