From 1c8c89dc62cfa4c9fa1e2888eb5459536853beb1 Mon Sep 17 00:00:00 2001
From: Ger Hobbelt <ger@hobbelt.com>
Date: Mon, 25 Dec 2017 01:20:37 +0100
Subject: [PATCH] BNF parser: produce stricter action code for arrow action in
 any jison 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                     |  2 +-
 .../parser-to-lexer-communication-test.jison  | 28 +++++++++----------
 packages/ebnf-parser/bnf.y                    |  5 +++-
 3 files changed, 19 insertions(+), 16 deletions(-)

diff --git a/examples/happyhappy.jison b/examples/happyhappy.jison
index 5f28b0522..2c11db0df 100644
--- a/examples/happyhappy.jison
+++ b/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(' ')
     ;
diff --git a/examples/parser-to-lexer-communication-test.jison b/examples/parser-to-lexer-communication-test.jison
index 7d6c7e953..44fd5ee75 100644
--- a/examples/parser-to-lexer-communication-test.jison
+++ b/examples/parser-to-lexer-communication-test.jison
@@ -44,7 +44,7 @@
 
 
 S
-    : init x x e                -> $e;
+    : init x x e                -> $e
     ;
 
 init
@@ -52,45 +52,45 @@ init
     ;
 
 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(); $$ = '}'; }
     ;
 
diff --git a/packages/ebnf-parser/bnf.y b/packages/ebnf-parser/bnf.y
index eb9494410..2e2a29b9e 100644
--- a/packages/ebnf-parser/bnf.y
+++ b/packages/ebnf-parser/bnf.y
@@ -807,7 +807,10 @@ action
     : action_ne
         { $$ = $action_ne; }
     | ARROW_ACTION
-        { $$ = '$$ = ' + $ARROW_ACTION; }
+        // add braces around ARROW_ACTION so that the action chunk test/compiler
+        // will uncover any illegal action code following the arrow operator, e.g.
+        // multiple statements separated by semicolon.
+        { $$ = '$$ = (' + $ARROW_ACTION + ');'; }
     | %epsilon
         { $$ = ''; }
     ;