deprecate FLASK_ENV

CHANGES.rst

@@ -23,6 +23,10 @@ Unreleased
         ``g`` instead using a unique prefix, like
         ``g._extension_name_attr``.
 
+-   The ``FLASK_ENV`` environment variable and ``app.env`` attribute are
+    deprecated, removing the distinction between development and debug
+    mode. Debug mode should be controlled directly using the ``--debug``
+    option or ``app.run(debug=True)``. :issue:`4714`
 -   Add new customization points to the ``Flask`` app object for many
     previously global behaviors.
 
@@ -60,9 +64,9 @@ Unreleased
     instance on every request. :issue:`2520`.
 -   A ``flask.cli.FlaskGroup`` Click group can be nested as a
     sub-command in a custom CLI. :issue:`3263`
--   Add ``--app``, ``--env``, and ``--debug`` options to the ``flask``
+-   Add ``--app`` and ``--debug`` options to the ``flask`` CLI, instead
-    CLI, instead of requiring that they are set through environment
+    of requiring that they are set through environment variables.
-    variables. :issue:`2836`
+    :issue:`2836`
 -   Add ``--env-file`` option to the ``flask`` CLI. This allows
     specifying a dotenv file to load in addition to ``.env`` and
     ``.flaskenv``. :issue:`3108`

src/flask/app.py

@@ -45,7 +45,6 @@ from .globals import request_ctx
 from .globals import session
 from .helpers import _split_blueprint_path
 from .helpers import get_debug_flag
-from .helpers import get_env
 from .helpers import get_flashed_messages
 from .helpers import get_load_dotenv
 from .helpers import locked_cached_property
@@ -691,7 +690,7 @@ class Flask(Scaffold):
         if instance_relative:
             root_path = self.instance_path
         defaults = dict(self.default_config)
-        defaults["ENV"] = get_env()
+        defaults["ENV"] = os.environ.get("FLASK_ENV") or "development"
         defaults["DEBUG"] = get_debug_flag()
         return self.config_class(root_path, defaults)
 
@@ -849,31 +848,50 @@ class Flask(Scaffold):
             rv.update(processor())
         return rv
 
-    #: What environment the app is running in. Flask and extensions may
+    @property
-    #: enable behaviors based on the environment, such as enabling debug
+    def env(self) -> str:
-    #: mode. This maps to the :data:`ENV` config key. This is set by the
+        """What environment the app is running in. This maps to the :data:`ENV` config
-    #: :envvar:`FLASK_ENV` environment variable and may not behave as
+        key.
-    #: expected if set in code.
+
-    #:
+        **Do not enable development when deploying in production.**
-    #: **Do not enable development when deploying in production.**
+
-    #:
+        Default: ``'production'``
-    #: Default: ``'production'``
+
-    env = ConfigAttribute("ENV")
+        .. deprecated:: 2.2
+            Will be removed in Flask 2.3.
+        """
+        import warnings
+
+        warnings.warn(
+            "'app.env' is deprecated and will be removed in Flask 2.3."
+            " Use 'app.debug' instead.",
+            DeprecationWarning,
+            stacklevel=2,
+        )
+        return self.config["ENV"]
+
+    @env.setter
+    def env(self, value: str) -> None:
+        import warnings
+
+        warnings.warn(
+            "'app.env' is deprecated and will be removed in Flask 2.3."
+            " Use 'app.debug' instead.",
+            DeprecationWarning,
+            stacklevel=2,
+        )
+        self.config["ENV"] = value
 
     @property
     def debug(self) -> bool:
-        """Whether debug mode is enabled. When using ``flask run`` to start
+        """Whether debug mode is enabled. When using ``flask run`` to start the
-        the development server, an interactive debugger will be shown for
+        development server, an interactive debugger will be shown for unhandled
-        unhandled exceptions, and the server will be reloaded when code
+        exceptions, and the server will be reloaded when code changes. This maps to the
-        changes. This maps to the :data:`DEBUG` config key. This is
+        :data:`DEBUG` config key. It may not behave as expected if set late.
-        enabled when :attr:`env` is ``'development'`` and is overridden
-        by the ``FLASK_DEBUG`` environment variable. It may not behave as
-        expected if set in code.
 
         **Do not enable debug mode when deploying in production.**
 
-        Default: ``True`` if :attr:`env` is ``'development'``, or
+        Default: ``False``
-        ``False`` otherwise.
         """
         return self.config["DEBUG"]
 
@@ -937,9 +955,7 @@ class Flask(Scaffold):
             If installed, python-dotenv will be used to load environment
             variables from :file:`.env` and :file:`.flaskenv` files.
 
-            If set, the :envvar:`FLASK_ENV` and :envvar:`FLASK_DEBUG`
+            The :envvar:`FLASK_DEBUG` environment variable will override :attr:`debug`.
-            environment variables will override :attr:`env` and
-            :attr:`debug`.
 
             Threaded mode is enabled by default.
 
@@ -966,7 +982,12 @@ class Flask(Scaffold):
 
             # if set, let env vars override previous values
             if "FLASK_ENV" in os.environ:
-                self.env = get_env()
+                print(
+                    "'FLASK_ENV' is deprecated and will not be used in"
+                    " Flask 2.3. Use 'FLASK_DEBUG' instead.",
+                    file=sys.stderr,
+                )
+                self.config["ENV"] = os.environ.get("FLASK_ENV") or "production"
                 self.debug = get_debug_flag()
             elif "FLASK_DEBUG" in os.environ:
                 self.debug = get_debug_flag()
@@ -998,7 +1019,7 @@ class Flask(Scaffold):
         options.setdefault("use_debugger", self.debug)
         options.setdefault("threaded", True)
 
-        cli.show_server_banner(self.env, self.debug, self.name)
+        cli.show_server_banner(self.debug, self.name)
 
         from werkzeug.serving import run_simple
 

src/flask/cli.py

@@ -13,12 +13,12 @@ from operator import attrgetter
 
 import click
 from click.core import ParameterSource
+from werkzeug import run_simple
 from werkzeug.serving import is_running_from_reloader
 from werkzeug.utils import import_string
 
 from .globals import current_app
 from .helpers import get_debug_flag
-from .helpers import get_env
 from .helpers import get_load_dotenv
 
 if t.TYPE_CHECKING:
@@ -418,29 +418,6 @@ _app_option = click.Option(
 )
 
 
-def _set_env(ctx: click.Context, param: click.Option, value: str | None) -> str | None:
-    if value is None:
-        return None
-
-    # Set with env var instead of ScriptInfo.load so that it can be
-    # accessed early during a factory function.
-    os.environ["FLASK_ENV"] = value
-    return value
-
-
-_env_option = click.Option(
-    ["-E", "--env"],
-    metavar="NAME",
-    help=(
-        "The execution environment name to set in 'app.env'. Defaults to"
-        " 'production'. 'development' will enable 'app.debug' and start the"
-        " debugger and reloader when running the server."
-    ),
-    expose_value=False,
-    callback=_set_env,
-)
-
-
 def _set_debug(ctx: click.Context, param: click.Option, value: bool) -> bool | None:
     # If the flag isn't provided, it will default to False. Don't use
     # that, let debug be set by env in that case.
@@ -460,7 +437,7 @@ def _set_debug(ctx: click.Context, param: click.Option, value: bool) -> bool | N
 
 _debug_option = click.Option(
     ["--debug/--no-debug"],
-    help="Set 'app.debug' separately from '--env'.",
+    help="Set debug mode.",
     expose_value=False,
     callback=_set_debug,
 )
@@ -516,12 +493,10 @@ class FlaskGroup(AppGroup):
     :param load_dotenv: Load the nearest :file:`.env` and :file:`.flaskenv`
         files to set environment variables. Will also change the working
         directory to the directory containing the first file found.
-    :param set_debug_flag: Set the app's debug flag based on the active
+    :param set_debug_flag: Set the app's debug flag.
-        environment
 
     .. versionchanged:: 2.2
-        Added the ``-A/--app``, ``-E/--env``, ``--debug/--no-debug``,
+        Added the ``-A/--app``, ``--debug/--no-debug``, ``-e/--env-file`` options.
-        and ``-e/--env-file`` options.
 
     .. versionchanged:: 2.2
         An app context is pushed when running ``app.cli`` commands, so
@@ -546,7 +521,7 @@ class FlaskGroup(AppGroup):
         # callback. This allows users to make a custom group callback
         # without losing the behavior. --env-file must come first so
         # that it is eagerly evaluated before --app.
-        params.extend((_env_file_option, _app_option, _env_option, _debug_option))
+        params.extend((_env_file_option, _app_option, _debug_option))
 
         if add_version_option:
             params.append(version_option)
@@ -737,26 +712,23 @@ def load_dotenv(path: str | os.PathLike | None = None) -> bool:
     return loaded  # True if at least one file was located and loaded.
 
 
-def show_server_banner(env, debug, app_import_path):
+def show_server_banner(debug, app_import_path):
     """Show extra startup messages the first time the server is run,
     ignoring the reloader.
     """
     if is_running_from_reloader():
         return
 
+    click.secho(
+        "WARNING: This is a development server. Do not use it in a production"
+        " deployment. Use a production WSGI server instead.",
+        fg="red",
+        bold=True,
+    )
+
     if app_import_path is not None:
         click.echo(f" * Serving Flask app '{app_import_path}'")
 
-    click.echo(f" * Environment: {env}")
-
-    if env == "production":
-        click.secho(
-            "   WARNING: This is a development server. Do not use it in"
-            " a production deployment.\n   Use a production WSGI server"
-            " instead.",
-            fg="red",
-        )
-
     if debug is not None:
         click.echo(f" * Debug mode: {'on' if debug else 'off'}")
 
@@ -925,8 +897,8 @@ def run_command(
     This server is for development purposes only. It does not provide
     the stability, security, or performance of production WSGI servers.
 
-    The reloader and debugger are enabled by default with the
+    The reloader and debugger are enabled by default with the '--debug'
-    '--env development' or '--debug' options.
+    option.
     """
     try:
         app = info.load_app()
@@ -953,9 +925,7 @@ def run_command(
     if debugger is None:
         debugger = debug
 
-    show_server_banner(get_env(), debug, info.app_import_path)
+    show_server_banner(debug, info.app_import_path)
-
-    from werkzeug.serving import run_simple
 
     run_simple(
         host,

src/flask/helpers.py

@@ -29,22 +29,41 @@ def get_env() -> str:
     """Get the environment the app is running in, indicated by the
     :envvar:`FLASK_ENV` environment variable. The default is
     ``'production'``.
+
+    .. deprecated:: 2.2
+        Will be removed in Flask 2.3.
     """
+    import warnings
+
+    warnings.warn(
+        "'FLASK_ENV' and 'get_env' are deprecated and will be removed"
+        " in Flask 2.3. Use 'FLASK_DEBUG' instead.",
+        DeprecationWarning,
+        stacklevel=2,
+    )
     return os.environ.get("FLASK_ENV") or "production"
 
 
 def get_debug_flag() -> bool:
-    """Get whether debug mode should be enabled for the app, indicated
+    """Get whether debug mode should be enabled for the app, indicated by the
-    by the :envvar:`FLASK_DEBUG` environment variable. The default is
+    :envvar:`FLASK_DEBUG` environment variable. The default is ``False``.
-    ``True`` if :func:`.get_env` returns ``'development'``, or ``False``
-    otherwise.
     """
     val = os.environ.get("FLASK_DEBUG")
 
     if not val:
-        return get_env() == "development"
+        env = os.environ.get("FLASK_ENV")
 
-    return val.lower() not in ("0", "false", "no")
+        if env is not None:
+            print(
+                "'FLASK_ENV' is deprecated and will not be used in"
+                " Flask 2.3. Use 'FLASK_DEBUG' instead.",
+                file=sys.stderr,
+            )
+            return env == "development"
+
+        return False
+
+    return val.lower() not in {"0", "false", "no"}
 
 
 def get_load_dotenv(default: bool = True) -> bool:

tests/test_helpers.py

@@ -6,7 +6,6 @@ import werkzeug.exceptions
 
 import flask
 from flask.helpers import get_debug_flag
-from flask.helpers import get_env
 
 
 class FakePath:
@@ -322,20 +321,6 @@ class TestHelpers:
             assert get_debug_flag() == expected_flag
         assert get_debug_flag() == expected_default_flag
 
-    @pytest.mark.parametrize(
-        "env, ref_env, debug",
-        [
-            ("", "production", False),
-            ("production", "production", False),
-            ("development", "development", True),
-            ("other", "other", False),
-        ],
-    )
-    def test_get_env(self, monkeypatch, env, ref_env, debug):
-        monkeypatch.setenv("FLASK_ENV", env)
-        assert get_debug_flag() == debug
-        assert get_env() == ref_env
-
     def test_make_response(self):
         app = flask.Flask(__name__)
         with app.test_request_context():