Strip out a then-invalid comment when --no-default-action is set fo…

…r the given grammar: the kernel code should not carry blatantly incorrect comments either after kernel stripping! Sideways related to zaach#341.

lib/jison.js

@@ -862,7 +862,7 @@ generator.buildProductions = function buildProductions(bnf, productions, nonterm
     // before all others: this way these tokens have the maximum chance to get assigned their ASCII value as symbol ID,
     // which helps debugging/diagnosis of generated grammars.
     // (This is why previously we had set `usedSymbolIdsLowIndex` to 127 instead of 3!)
-    
+
     var prodsLUT = {};
     for (symbol in bnf) {
         if (!bnf.hasOwnProperty(symbol)) continue;
@@ -975,7 +975,7 @@ generator.buildProductions = function buildProductions(bnf, productions, nonterm
             }
             rhs = rhs.substr(pos + 1);
             // now find the matching end marker.
-            // 
+            //
             // Edge case: token MAY include the ESCAPED MARKER... or other escapes!
             // Hence we need to skip over ALL escapes inside the token!
             var pos3 = rhs.indexOf('\\');
@@ -1315,7 +1315,7 @@ generator.buildProductionActions = function buildProductionActions() {
         .replace(/\x01\x1B/g, 'yysp');
 
         // And a final, minimal, fixup for the semicolon-lovers -- like me! ;-)
-        // 
+        //
         // Make sure the last statement is properly semicolon-terminated 99.9% of the time:
         s = s
         .replace(/[\s\r\n]+$/, '')          // trim trailing whitespace and empty lines
@@ -1334,7 +1334,7 @@ generator.buildProductionActions = function buildProductionActions() {
 
     // and now go and process the entire grammar:
     productions.forEach(buildProductionAction);
-    
+
     for (var hash in actionGroups) {
         actions.push([].concat.apply([], actionGroups[hash]).join('') + actionGroupValue[hash] + '\n    break;\n');
     }
@@ -3228,9 +3228,17 @@ function removeUnusedKernelFeatures(parseFn, info) {
          *
          *     // perform semantic action
          *     yyval.$ = vstack[sp - len]; // default to $$ = $1
+         *
+         * and this bit of comment:
+         *
+         *     // Make sure subsequent `$$ = $1` default action doesn't fail
+         *     // for rules where len==0 as then there's no $1 (you're reducing an epsilon rule then!)
+         *     //
+         *     // Also do this ...
          */
         parseFn = parseFn
-        .replace(/\s+\/\/ perform semantic action\n\s+yyval\.\$ = vstack\[sp - [^\n]+\n/g, '\n\n');
+        .replace(/\s+\/\/ perform semantic action\n\s+yyval\.\$ = vstack\[sp - [^\n]+\n/g, '\n\n')
+        .replace(/\s+\/\/ Make sure subsequent `\$\$ = \$1` default action doesn't fail\n[^\n]+\n[^\n]+\n(\s+\/\/ )Also do this/g, '\n\n\n\n\n$1Do this');
     }
 
     if (info.options.noTryCatch) {