Fix handling of delimiter characters as part of bare words

Fixes atom/atom#18387

corpus/literals.txt

@@ -23,8 +23,8 @@ echo ]]] ===
 
 (program
   (command (command_name (word)) (concatenation (word) (word)))
-  (command (command_name (word)) (word))
-  (command (command_name (word)) (word) (word)))
+  (command (command_name (word)) (concatenation))
+  (command (command_name (word)) (concatenation) (word)))
 
 =============================
 Simple variable expansions
@@ -142,6 +142,7 @@ Other variable expansion operators
 ===================================
 
 cat ${BAR} ${ABC=def} ${GHI:?jkl}
+[ "$a" != "${a#[Bc]}" ]
 
 ---
 
@@ -150,7 +151,11 @@ cat ${BAR} ${ABC=def} ${GHI:?jkl}
     (command_name (word))
     (expansion (variable_name))
     (expansion (variable_name) (word))
-    (expansion (variable_name) (word))))
+    (expansion (variable_name) (word)))
+  (test_command
+    (binary_expression
+      (string (simple_expansion (variable_name)))
+      (string (expansion (variable_name) (concatenation (word)))))))
 
 =============================
 Command substitutions

grammar.js

@@ -378,7 +378,7 @@ module.exports = grammar({
     _literal: $ => choice(
       $.concatenation,
       $._primary_expression,
-      alias(prec(-2, $._special_characters), $.word)
+      alias(prec(-2, repeat1($._special_character)), $.word)
     ),
 
     _primary_expression: $ => choice(
@@ -395,18 +395,18 @@ module.exports = grammar({
     concatenation: $ => prec(-1, seq(
       choice(
         $._primary_expression,
-        $._special_characters,
+        $._special_character,
       ),
       repeat1(prec(-1, seq(
         $._concat,
         choice(
           $._primary_expression,
-          $._special_characters,
+          $._special_character,
         )
       ))),
     )),
 
-    _special_characters: $ => token(prec(-1, repeat1(choice('{', '}', '[', ']')))),
+    _special_character: $ => token(prec(-1, choice('{', '}', '[', ']'))),
 
     string: $ => seq(
       '"',

src/grammar.json

@@ -1518,9 +1518,12 @@
           "content": {
             "type": "PREC",
             "value": -2,
+            "content": {
+              "type": "REPEAT1",
               "content": {
                 "type": "SYMBOL",
-              "name": "_special_characters"
+                "name": "_special_character"
+              }
             }
           },
           "named": true,
@@ -1580,7 +1583,7 @@
               },
               {
                 "type": "SYMBOL",
-                "name": "_special_characters"
+                "name": "_special_character"
               }
             ]
           },
@@ -1605,7 +1608,7 @@
                       },
                       {
                         "type": "SYMBOL",
-                        "name": "_special_characters"
+                        "name": "_special_character"
                       }
                     ]
                   }
@@ -1616,13 +1619,11 @@
         ]
       }
     },
-    "_special_characters": {
+    "_special_character": {
       "type": "TOKEN",
       "content": {
         "type": "PREC",
         "value": -1,
-        "content": {
-          "type": "REPEAT1",
         "content": {
           "type": "CHOICE",
           "members": [
@@ -1645,7 +1646,6 @@
           ]
         }
       }
-      }
     },
     "string": {
       "type": "SEQ",