Bring back previous typerState after suspending a compilation unit

This is to avaoid unfulfilled constraints when
going through -Ycheck later.

Author: jchyb

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

@@ -375,6 +375,7 @@ object Phases {
       val doCheckJava = skipIfJava && !isAfterLastJavaPhase
       for unit <- units do ctx.profiler.onUnit(this, unit):
         given unitCtx: Context = runCtx.fresh.setPhase(this.start).setCompilationUnit(unit).withRootImports
+        val previousTyperState = unitCtx.typerState.snapshot()
         if ctx.run.enterUnit(unit) then
           try
             if doCheckJava && unit.typedAsJava then
@@ -384,6 +385,7 @@ object Phases {
             buf += unitCtx.compilationUnit
           catch
             case _: CompilationUnit.SuspendException => // this unit will be run again in `Run#compileSuspendedUnits`
+              unitCtx.typerState.resetTo(previousTyperState)
             case ex: Throwable if !ctx.run.enrichedErrorMessage =>
               println(ctx.run.enrichErrorMessage(s"unhandled exception while running $phaseName on $unit"))
               throw ex

tests/pos/i21176-b/Macro.scala

@@ -0,0 +1,9 @@
+import scala.quoted.*
+
+class Macro:
+  inline def nameTuple[NameTuple_T]: (String, List[NameTuple_T]) = Macro.tuple[NameTuple_T](Macro.named)
+
+object Macro:
+  def namedMacro(using q: Quotes): Expr[String] = Expr("test")
+  inline def named: String = ${Macro.namedMacro}
+  def tuple[Tuple_T](name: String): (String, List[Tuple_T]) = (name, List.empty[Tuple_T])

tests/pos/i21176-b/Main.scala

@@ -0,0 +1,2 @@
+class Test extends Macro:
+  val abc = nameTuple[Int]