Correct the pattern for checking if a dynamic symbol can be converted into a label as a hash key.

CHANGELOG.md

@@ -6,6 +6,10 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/) a
 
 ## [Unreleased]
 
+### Changed
+
+- Correct the pattern for checking if a dynamic symbol can be converted into a label as a hash key.
+
 ## [2.4.1] - 2022-05-10
 
 - [#73](https://github.com/ruby-syntax-tree/syntax_tree/pull/73) - Fix nested hash patterns from accidentally adding a `then` to their output.

lib/syntax_tree/node.rb

@@ -1388,7 +1388,7 @@ def format(q)
   module HashKeyFormatter
     # Formats the keys of a hash literal using labels.
     class Labels
-      LABEL = /^[@$_A-Za-z]([_A-Za-z0-9]*)?([!_=?A-Za-z0-9])?$/
+      LABEL = /\A[A-Za-z_](\w*[\w!?])?\z/
 
       def format_key(q, key)
         case key

test/fixtures/assoc.rb

@@ -46,3 +46,5 @@
 { foo: "bar" }
 %
 { "foo #{bar}": "baz" }
+%
+{ "foo=": "baz" }