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)