feat: add using declaration

Author: amaanq

grammar.js

@@ -181,6 +181,7 @@ module.exports = grammar({
       $.class_declaration,
       $.lexical_declaration,
       $.variable_declaration,
+      $.using_declaration,
     ),
 
     //
@@ -286,6 +287,15 @@ module.exports = grammar({
       $._semicolon,
     ),
 
+    using_declaration: $ => seq(
+      field('kind', choice(
+        'using',
+        seq('await', 'using'),
+      )),
+      commaSep1($.variable_declarator),
+      $._semicolon,
+    ),
+
     variable_declarator: $ => seq(
       field('name', choice($.identifier, $._destructuring_pattern)),
       optional($._initializer),
@@ -360,6 +370,17 @@ module.exports = grammar({
           )),
           optional($._automatic_semicolon),
         ),
+        seq(
+          field('kind', choice(
+            'using',
+            seq('await', 'using'),
+          )),
+          field('left', choice(
+            $.identifier,
+            $._destructuring_pattern,
+          )),
+          optional($._automatic_semicolon),
+        ),
       ),
       field('operator', choice('in', 'of')),
       field('right', $._expressions),

test/corpus/statements.txt

@@ -870,6 +870,71 @@ var x, y = {}, z;
     (variable_declarator
       (identifier))))
 
+============================================
+Using declarations
+============================================
+
+using file = getFile();
+await using resource = getResource();
+using x = a, y = b;
+
+---
+
+(program
+  (using_declaration
+    (variable_declarator
+      (identifier)
+      (call_expression
+        (identifier)
+        (arguments))))
+  (using_declaration
+    (variable_declarator
+      (identifier)
+      (call_expression
+        (identifier)
+        (arguments))))
+  (using_declaration
+    (variable_declarator
+      (identifier)
+      (identifier))
+    (variable_declarator
+      (identifier)
+      (identifier))))
+
+============================================
+Using declarations in for loops
+============================================
+
+for (using item of items) {
+  process(item);
+}
+
+for await (await using resource of resources) {
+  consume(resource);
+}
+
+---
+
+(program
+  (for_in_statement
+    (identifier)
+    (identifier)
+    (statement_block
+      (expression_statement
+        (call_expression
+          (identifier)
+          (arguments
+            (identifier))))))
+  (for_in_statement
+    (identifier)
+    (identifier)
+    (statement_block
+      (expression_statement
+        (call_expression
+          (identifier)
+          (arguments
+            (identifier)))))))
+
 ============================================
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