Change default target to jvm-9 in test

Author: liufengyun

Diff for: compiler/src/dotty/tools/backend/jvm/BCodeSkelBuilder.scala

@@ -129,7 +129,7 @@ trait BCodeSkelBuilder extends BCodeHelpers {
         // reverse all the effects of this transformation, which would be counter-productive.
 
 
-        // TODO: enable once we change lazy val encoding
+        // TODO: enable once we change lazy val encoding (https://github.com/lampepfl/dotty/issues/7140)
         //
         // Lazy val encoding assumes bitmap fields are non-static
         //

Diff for: compiler/test/dotty/tools/vulpix/TestConfiguration.scala

@@ -8,7 +8,8 @@ object TestConfiguration {
 
   val noCheckOptions = Array(
     "-pagewidth", "120",
-    "-color:never"
+    "-color:never",
+    "-target", defaultTarget
   )
 
   val checkOptions = Array(
@@ -76,4 +77,20 @@ object TestConfiguration {
 
   /** Enables explicit nulls */
   val explicitNullsOptions = defaultOptions and "-Yexplicit-nulls"
+
+  /** Default target of the generated class files */
+  private def defaultTarget: String = {
+    val javaVersion: Int =
+      if (Properties.javaVersion.startsWith("1.")) {
+        Properties.javaVersion.substring(2, 3).toInt
+      }
+      else {
+        val dot = Properties.javaVersion.indexOf(".")
+        assert(dot != -1, "unknown java version: " + Properties.javaVersion)
+        Properties.javaVersion.substring(0, dot).toInt
+      }
+
+    if (javaVersion < 9) "jvm-1.8"
+    else "jvm-9"
+  }
 }