jflex: add %no_suppress_warnings directive

By default JFlex emits @SuppressWarnings("fallthrough") at the class
level. This directive removes that annotation and leaves it up to the
user to define their own.

Fixes #762

jflex/src/main/java/jflex/core/AbstractLexScan.java

@@ -67,6 +67,7 @@ public enum CharSetSize {
   boolean standalone;
   boolean debugOption;
   boolean eofclose;
+  boolean noSuppressWarnings;
 
   String isImplementing;
   String isExtending;
@@ -395,6 +396,10 @@ public int bufferSize() {
     return bufferSize;
   }
 
+  public boolean noSuppressWarnings() {
+    return noSuppressWarnings;
+  }
+
   /**
    * Returns the current line number.
    *

jflex/src/main/java/jflex/generator/Emitter.java

@@ -429,9 +429,10 @@ private void emitUserCode() {
   }
 
   private void emitClassName() {
-    // TODO(#222) Actually fix the fall-through violations
-    println("// See https://github.com/jflex-de/jflex/issues/222");
-    println("@SuppressWarnings(\"FallThrough\")");
+    if (!scanner.noSuppressWarnings()) {
+      // TODO(#222) Actually fix the fall-through violations
+      println("@SuppressWarnings(\"fallthrough\")");
+    }
     if (scanner.isPublic()) print("public ");
 
     if (scanner.isAbstract()) print("abstract ");

jflex/src/main/jflex/LexScan.flex

@@ -281,6 +281,8 @@ DottedVersion =  [1-9][0-9]*(\.[0-9]+){0,2}
   "%warn" {WSP}+ {WarningIdent} {WSP}* { OptionUtils.enableWarning(yytext().substring(6).trim()); }
   "%warn" {WSP}+ {NNL}* { throw new ScannerException(file, ErrorMessages.NOT_A_WARNING_ID, yyline); }
 
+  "%no_suppress_warnings" {WSP}* { noSuppressWarnings = true; }
+
   {Ident}                     { return symbol(IDENT, yytext()); }
   "="{WSP}*                   { yybegin(REGEXP);
                                 return symbol(EQUALS);