Lift arguments to defs instead of vals in coverage

possible fix for lampepfl#16940

Author: KacperFKorban

compiler/src/dotty/tools/dotc/typer/EtaExpansion.scala

@@ -194,6 +194,10 @@ object LiftCoverage extends LiftImpure {
     val liftedArgs = liftArgs(defs, tree.fun.tpe, tree.args)(using liftingArgsContext)
     tpd.cpy.Apply(tree)(liftedFun, liftedArgs)
   }
+
+  override def liftedFlags: FlagSet = Method
+
+  override def liftedDef(sym: TermSymbol, rhs: tpd.Tree)(using Context): tpd.DefDef = tpd.DefDef(sym, rhs)
 }
 
 object LiftErased extends LiftComplex:

tests/run/i16940.scala

@@ -0,0 +1,30 @@
+// scalac: -coverage-out:coverage
+// scalajs: --skip
+
+import concurrent.ExecutionContext.Implicits.global
+import scala.concurrent.*
+import scala.concurrent.duration.*
+
+var test = 0
+
+def brokenSynchronizedBlock(option: Boolean): Future[Unit] = Future {
+  if (option) {
+    Thread.sleep(500)
+  }
+  synchronized {
+    val tmp = test
+    Thread.sleep(1000)
+    test = tmp + 1
+  }
+}
+
+object Test extends App {
+  Await.result(
+    Future.sequence(Seq(brokenSynchronizedBlock(false), brokenSynchronizedBlock(true)))
+      .map { result =>
+        println(test)
+        assert(test == 2)
+      },
+    3.seconds
+  )
+}