fix: disallow ';;' as a terminator for C-style for loops

grammar.js

@@ -154,7 +154,7 @@ module.exports = grammar({
     c_style_for_statement: $ => seq(
       'for',
       '((',
-      choice($._for_body, ';;'),
+      choice($._for_body),
       '))',
       optional(';'),
       field('body', choice(
@@ -164,9 +164,9 @@ module.exports = grammar({
     ),
     _for_body: $ => seq(
       field('initializer', commaSep($._c_expression)),
-      $._terminator,
+      $._c_terminator,
       field('condition', commaSep($._c_expression)),
-      $._terminator,
+      $._c_terminator,
       field('update', commaSep($._c_expression)),
     ),
 
@@ -684,6 +684,7 @@ module.exports = grammar({
 
     test_operator: _ => token(prec(1, seq('-', /[a-zA-Z]+/))),
 
+    _c_terminator: _ => choice(';', '\n', '&'),
     _terminator: _ => choice(';', ';;', '\n', '&'),
   },
 });

test/corpus/statements.txt

@@ -301,6 +301,8 @@ for ((cx = 0; c = $cx / $pf, c < $wc - $k; )); do
 		echo "$cx"
 done
 
+for (( i = 4;;i--)) ; do echo $i; if (( $i == 0 )); then break; fi; done
+
 --------------------------------------------------------------------------------
 
 (program
@@ -364,7 +366,28 @@ done
           (word))
         (string
           (simple_expansion
-            (variable_name)))))))
+            (variable_name))))))
+  (c_style_for_statement
+    (variable_assignment
+      (variable_name)
+      (number))
+    (postfix_expression
+      (word))
+    (do_group
+      (command
+        (command_name
+          (word))
+        (simple_expansion
+          (variable_name)))
+      (if_statement
+        (test_command
+          (binary_expression
+            (simple_expansion
+              (variable_name))
+            (regex)))
+        (command
+          (command_name
+            (word)))))))
 
 ================================================================================
 If statements