Add error recovery in for loops

grammar.coffee

@@ -71,9 +71,9 @@ module.exports = compiler.grammar
     for_statement: -> seq(
       keyword("for"),
       "(",
-      commaSep(@expression), ";"
-      optional(@expression), ";"
-      optional(@expression),
+      commaSep(err(@expression)), ";"
+      optional(err(@expression)), ";"
+      optional(err(@expression)),
       ")",
       @statement)
 

grammar_test/errors.txt

@@ -35,6 +35,48 @@ okWhatever();
     (expression_statement (function_call (identifier))))
   (expression_statement (function_call (identifier))))
 
+============================================
+Invalid for loops
+============================================
+
+for (i = 0; a b c d e; i++)
+  wat();
+
+ok1;
+
+for (a b c d; e; i++)
+  wat();
+
+ok2;
+
+for (a; b; c d e f)
+  wat();
+
+---
+
+(program
+  (for_statement
+    (assignment (identifier) (number))
+    (ERROR 'b')
+    (math_op (identifier))
+    (expression_statement (function_call (identifier))))
+
+  (expression_statement (identifier))
+
+  (for_statement
+    (ERROR 'b')
+    (identifier)
+    (math_op (identifier))
+    (expression_statement (function_call (identifier))))
+
+  (expression_statement (identifier))
+
+  (for_statement
+    (identifier)
+    (identifier)
+    (ERROR 'd')
+    (expression_statement (function_call (identifier)))))
+
 ============================================
 Invalid statement blocks
 ============================================