Fix test source-dependencies/ext

sbt-dotty/sbt-test/source-dependencies/ext/build.sbt

@@ -3,7 +3,9 @@ import complete.DefaultParsers._
 val checkIterations = inputKey[Unit]("Verifies the accumlated number of iterations of incremental compilation.")
 
 checkIterations := {
-	val expected: Int = (Space ~> NatBasic).parsed
-	val actual: Int = (compile in Compile).value.compilations.allCompilations.size
-	assert(expected == actual, s"Expected $expected compilations, got $actual")
+  val analysis = (compile in Compile).value.asInstanceOf[sbt.internal.inc.Analysis]
+
+  val expected: Int = (Space ~> NatBasic).parsed
+  val actual: Int = analysis.compilations.allCompilations.size
+  assert(expected == actual, s"Expected $expected compilations, got $actual")
 }