Require that grammars' start rules be visible

test/fixtures/error_corpus/json_errors.txt

@@ -25,10 +25,11 @@ errors inside arrays
 [1, , 2]
 
 ---
-(array
+
+(value (array
   (number)
   (ERROR)
-  (number))
+  (number)))
 
 ==========================================
 errors inside objects
@@ -38,7 +39,9 @@ errors inside objects
 
 ---
 
-(object (pair (string) (number)) (ERROR (UNEXPECTED 'o')))
+(value (object
+  (pair (string) (number))
+  (ERROR (UNEXPECTED 'o'))))
 
 ==========================================
 errors inside nested objects
@@ -48,9 +51,9 @@ errors inside nested objects
 
 ---
 
-(object
+(value (object
   (pair (string) (object
     (pair (string) (number))
     (ERROR (number))))
   (ERROR)
-  (pair (string) (number)))
+  (pair (string) (number))))

test/fixtures/test_grammars/inline_rules/grammar.json

@@ -17,6 +17,7 @@
         "name": "statement"
       }
     },
+
     "statement": {
       "type": "SEQ",
       "members": [

test/fixtures/test_grammars/invisible_start_rule/expected_error.txt

@@ -0,0 +1 @@
+A grammar's start rule must be visible.

test/fixtures/test_grammars/invisible_start_rule/grammar.json

@@ -0,0 +1,23 @@
+{
+  "name": "invisible_start_rule",
+
+  "rules": {
+    "_value": {
+      "type": "CHOICE",
+      "members": [
+        {"type": "SYMBOL", "name": "a"},
+        {"type": "SYMBOL", "name": "b"}
+      ]
+    },
+
+    "a": {
+      "type": "STRING",
+      "value": "a"
+    },
+
+    "b": {
+      "type": "STRING",
+      "value": "b"
+    }
+  }
+}