Revert "Don't parse square bracket commands as special syntax"

This reverts commit c34619a1c4.

Bracket command syntax was actually not interfering with the parsing
of words with special characters.

corpus/control_flow.txt

@@ -93,12 +93,10 @@ fi
 
 (program
   (if_statement
-    (command
-      (command_name (word))
+    (bracket_command
       (string (command_substitution (command (command_name (word)))))
       (word)
-      (raw_string)
-      (word))
+      (raw_string))
     (command (command_name (word)) (word))))
 
 ====================================

corpus/expressions.txt

@@ -27,12 +27,10 @@ echo ]]] ===
   (command (command_name (word)) (word))
   (command (command_name (word)) (word) (word))
   (list
-    (command
-      (command_name (word))
+    (bracket_command
       (string)
       (word)
-      (concatenation (word) (word))
-      (word))
+      (concatenation (word) (word)))
     (command
       (command_name (word))
       (concatenation (word)))))

grammar.js

@@ -56,6 +56,7 @@ module.exports = grammar({
       $.variable_assignment,
       $.command,
       $.declaration_command,
+      $.bracket_command,
       $.for_statement,
       $.while_statement,
       $.if_statement,
@@ -178,6 +179,11 @@ module.exports = grammar({
       $._statement
     )),
 
+    bracket_command: $ => choice(
+      seq('[', repeat1($._expression), ']'),
+      seq('[[', repeat1($._expression), ']]')
+    ),
+
     // Commands
 
     command: $ => prec.left(seq(

src/grammar.json

@@ -36,6 +36,10 @@
           "type": "SYMBOL",
           "name": "declaration_command"
         },
+        {
+          "type": "SYMBOL",
+          "name": "bracket_command"
+        },
         {
           "type": "SYMBOL",
           "name": "for_statement"
@@ -593,6 +597,51 @@
         ]
       }
     },
+    "bracket_command": {
+      "type": "CHOICE",
+      "members": [
+        {
+          "type": "SEQ",
+          "members": [
+            {
+              "type": "STRING",
+              "value": "["
+            },
+            {
+              "type": "REPEAT1",
+              "content": {
+                "type": "SYMBOL",
+                "name": "_expression"
+              }
+            },
+            {
+              "type": "STRING",
+              "value": "]"
+            }
+          ]
+        },
+        {
+          "type": "SEQ",
+          "members": [
+            {
+              "type": "STRING",
+              "value": "[["
+            },
+            {
+              "type": "REPEAT1",
+              "content": {
+                "type": "SYMBOL",
+                "name": "_expression"
+              }
+            },
+            {
+              "type": "STRING",
+              "value": "]]"
+            }
+          ]
+        }
+      ]
+    },
     "command": {
       "type": "PREC_LEFT",
       "value": 0,