fix default value of app.env

Author: davidism

CHANGES.rst

@@ -3,6 +3,9 @@ Version 2.2.2
 
 Unreleased
 
+-   Fix the default value for ``app.env`` to be ``"production"``. This
+    attribute remains deprecated. :issue:`4740`
+
 
 Version 2.2.1
 -------------

src/flask/app.py

@@ -827,7 +827,7 @@ def make_config(self, instance_relative: bool = False) -> Config:
         if instance_relative:
             root_path = self.instance_path
         defaults = dict(self.default_config)
-        defaults["ENV"] = os.environ.get("FLASK_ENV") or "development"
+        defaults["ENV"] = os.environ.get("FLASK_ENV") or "production"
         defaults["DEBUG"] = get_debug_flag()
         return self.config_class(root_path, defaults)