BNF parser: produce stricter action code for arrow action in any jiso…

…n grammar so that we can more easily check coding mistakes in a production's arrow code, e.g. unwanted semicolons, multiple statements, etc., which can currently slip through the net and cause hard-to-diagnose havoc down the line.

examples/happyhappy.jison

@@ -44,5 +44,5 @@ e
     ;
 
 phrase
-    : 'happy' 'happy' 'joy' 'joy'  -> [$1, $2, $3, $4].join(' ');
+    : 'happy' 'happy' 'joy' 'joy'  -> [$1, $2, $3, $4].join(' ')
     ;

examples/parser-to-lexer-communication-test.jison

@@ -44,53 +44,53 @@
 
 
 S
-    : init x x e                -> $e;
+    : init x x e                -> $e
     ;
 
 init
     : %epsilon                  
     ;
 
 x
-    : %epsilon                  -> '<X-epsilon>';
+    : %epsilon                  -> '<X-epsilon>'
     ;
 
 e
-    : cmd e                     -> $cmd + ' | ' + $e;
-    | %epsilon                  -> '<E-epsilon>';
+    : cmd e                     -> $cmd + ' | ' + $e
+    | %epsilon                  -> '<E-epsilon>'
     ;
 
 cmd
-    : a                         -> $a;
-    | f_a                       -> $f_a;
-    | b                         -> $b;
-    | f_b                       -> $f_b;
+    : a                         -> $a
+    | f_a                       -> $f_a
+    | b                         -> $b
+    | f_b                       -> $f_b
     | error                     { yyerrok; yyclearin; $$ = 'ERROR'; }
     ;
 
 a
-    : A                         -> 'A[' + $A + ']';
+    : A                         -> 'A[' + $A + ']'
     ;
 
 f_a
-    : A lb e rb                 -> 'A' + $lb + $e + $rb;
+    : A lb e rb                 -> 'A' + $lb + $e + $rb
     ;
 
 b
-    : B                         -> 'B[' + $B + ']';
+    : B                         -> 'B[' + $B + ']'
     ;
 
 f_b
-    : B lb e rb                 -> 'B' + $lb + $e + $rb;
+    : B lb e rb                 -> 'B' + $lb + $e + $rb
     ;
 
 lb
     : '('                       { yylexer.pushState('alt'); $$ = '('; }
-    | BEGIN                     -> '{';
+    | BEGIN                     -> '{'
     ;
 
 rb
-    : ')'                       -> ')';
+    : ')'                       -> ')'
     | END                       { yylexer.popState(); $$ = '}'; }
     ;
 

packages/ebnf-parser/bnf.y

@@ -807,7 +807,10 @@ action
     : action_ne
         { $$ = $action_ne; }
     | ARROW_ACTION
-        { $$ = '$$ = ' + $ARROW_ACTION; }
+        // add braces around ARROW_ACTION so that the action chunk test/compiler
+        // will uncover any illegal action code following the arrow operator, e.g.
+        // multiple statements separated by semicolon.
+        { $$ = '$$ = (' + $ARROW_ACTION + ');'; }
     | %epsilon
         { $$ = ''; }
     ;