Add special variable @, expressions in declarations

corpus/expressions.txt

@@ -48,6 +48,21 @@ echo $abc
 (program
   (command (command_name (word)) (simple_expansion (variable_name))))
 
+=============================
+Special variable expansions
+=============================
+
+echo $# $* $@
+
+---
+
+(program
+  (command
+    (command_name (word))
+    (simple_expansion (special_variable_name))
+    (simple_expansion (special_variable_name))
+    (simple_expansion (special_variable_name))))
+
 =============================
 Variable expansions
 =============================
@@ -286,6 +301,23 @@ export FOOBAR PATH="$PATH:/usr/foobar/bin"
     (variable_name)
     (variable_assignment (variable_name) (string (simple_expansion (variable_name))))))
 
+===========================================
+Expressions passed to declaration commands
+===========================================
+
+export "$(echo ${key} | tr [:lower:] [:upper:])=${p_key#*=}"
+
+---
+
+(program
+  (declaration_command
+    (string
+      (command_substitution
+        (pipeline
+          (command (command_name (word)) (expansion (variable_name)))
+          (command (command_name (word)) (concatenation (word)) (concatenation (word)))))
+      (expansion (variable_name) (word)))))
+
 =========================================
 Arrays and array expansions
 =========================================

grammar.js

@@ -204,14 +204,14 @@ module.exports = grammar({
       $._assignment
     ),
 
-    declaration_command: $ => seq(
+    declaration_command: $ => prec.left(seq(
       choice('declare', 'typeset', 'export', 'readonly', 'local'),
       repeat(choice(
-        $.word,
+        $._expression,
         $._simple_variable_name,
         $.variable_assignment
       ))
-    ),
+    )),
 
     _assignment: $ => seq(
       choice(
@@ -323,7 +323,12 @@ module.exports = grammar({
 
     simple_expansion: $ => seq(
       '$',
-      choice($._simple_variable_name, $._special_variable_name)
+      choice(
+        $._simple_variable_name,
+        $._special_variable_name,
+        alias('#', $.special_variable_name),
+        $.string
+      )
     ),
 
     expansion: $ => seq(

src/grammar.json

@@ -676,6 +676,9 @@
       ]
     },
     "declaration_command": {
+      "type": "PREC_LEFT",
+      "value": 0,
+      "content": {
         "type": "SEQ",
         "members": [
           {
@@ -710,7 +713,7 @@
               "members": [
                 {
                   "type": "SYMBOL",
-                "name": "word"
+                  "name": "_expression"
                 },
                 {
                   "type": "SYMBOL",
@@ -724,6 +727,7 @@
             }
           }
         ]
+      }
     },
     "_assignment": {
       "type": "SEQ",
@@ -1180,6 +1184,19 @@
             {
               "type": "SYMBOL",
               "name": "_special_variable_name"
+            },
+            {
+              "type": "ALIAS",
+              "content": {
+                "type": "STRING",
+                "value": "#"
+              },
+              "named": true,
+              "value": "special_variable_name"
+            },
+            {
+              "type": "SYMBOL",
+              "name": "string"
             }
           ]
         }