src/jdk.compiler/share/classes/com/sun/tools/javac/code/Source.java

@@ -129,10 +129,14 @@
 
     public static Source lookup(String name) {
         return tab.get(name);
     }
 
+    public boolean isSupported() {
+        return this.compareTo(MIN) >= 0;
+    }
+
     public Target requiredTarget() {
         if (this.compareTo(JDK12) >= 0) return Target.JDK1_12;
         if (this.compareTo(JDK11) >= 0) return Target.JDK1_11;
         if (this.compareTo(JDK10) >= 0) return Target.JDK1_10;
         if (this.compareTo(JDK9) >= 0) return Target.JDK1_9;