inline conditional imports for cli behaviors

setup.cfg

@@ -116,3 +116,6 @@ ignore_missing_imports = True
 
 [mypy-cryptography.*]
 ignore_missing_imports = True
+
+[mypy-importlib_metadata]
+ignore_missing_imports = True

src/flask/cli.py

@@ -9,8 +9,6 @@ from functools import update_wrapper
 from operator import attrgetter
 from threading import Lock
 from threading import Thread
-from typing import Any
-from typing import TYPE_CHECKING
 
 import click
 from werkzeug.utils import import_string
@@ -20,31 +18,6 @@ from .helpers import get_debug_flag
 from .helpers import get_env
 from .helpers import get_load_dotenv
 
-try:
-    import dotenv
-except ImportError:
-    dotenv = None
-
-try:
-    import ssl
-except ImportError:
-    ssl = None  # type: ignore
-
-if sys.version_info >= (3, 10):
-    from importlib import metadata
-else:
-    # Use a backport on Python < 3.10.
-    #
-    # We technically have importlib.metadata on 3.8+,
-    # but the API changed in 3.10, so use the backport
-    # for consistency.
-    if TYPE_CHECKING:
-        metadata: Any
-    else:
-        # we do this to avoid a version dependent mypy error
-        # because importlib_metadata is not installed in python3.10+
-        import importlib_metadata as metadata
-
 
 class NoAppException(click.UsageError):
     """Raised if an application cannot be found or loaded."""
@@ -520,6 +493,14 @@ class FlaskGroup(AppGroup):
         if self._loaded_plugin_commands:
             return
 
+        if sys.version_info >= (3, 10):
+            from importlib import metadata
+        else:
+            # Use a backport on Python < 3.10. We technically have
+            # importlib.metadata on 3.8+, but the API changed in 3.10,
+            # so use the backport for consistency.
+            import importlib_metadata as metadata
+
         for ep in metadata.entry_points(group="flask.commands"):
             self.add_command(ep.load(), ep.name)
 
@@ -615,7 +596,9 @@ def load_dotenv(path=None):
 
     .. versionadded:: 1.0
     """
-    if dotenv is None:
+    try:
+        import dotenv
+    except ImportError:
         if path or os.path.isfile(".env") or os.path.isfile(".flaskenv"):
             click.secho(
                 " * Tip: There are .env or .flaskenv files present."
@@ -691,12 +674,14 @@ class CertParamType(click.ParamType):
         self.path_type = click.Path(exists=True, dir_okay=False, resolve_path=True)
 
     def convert(self, value, param, ctx):
-        if ssl is None:
+        try:
+            import ssl
+        except ImportError:
             raise click.BadParameter(
                 'Using "--cert" requires Python to be compiled with SSL support.',
                 ctx,
                 param,
-            )
+            ) from None
 
         try:
             return self.path_type(value, param, ctx)
@@ -729,7 +714,13 @@ def _validate_key(ctx, param, value):
     """
     cert = ctx.params.get("cert")
     is_adhoc = cert == "adhoc"
-    is_context = ssl and isinstance(cert, ssl.SSLContext)
+
+    try:
+        import ssl
+    except ImportError:
+        is_context = False
+    else:
+        is_context = isinstance(cert, ssl.SSLContext)
 
     if value is not None:
         if is_adhoc:

tests/test_cli.py

@@ -18,7 +18,6 @@ from flask import current_app
 from flask import Flask
 from flask.cli import AppGroup
 from flask.cli import DispatchingApp
-from flask.cli import dotenv
 from flask.cli import find_best_app
 from flask.cli import FlaskGroup
 from flask.cli import get_version
@@ -492,7 +491,18 @@ class TestRoutes:
         assert "No routes were registered." in result.output
 
 
-need_dotenv = pytest.mark.skipif(dotenv is None, reason="dotenv is not installed")
+def dotenv_not_available():
+    try:
+        import dotenv  # noqa: F401
+    except ImportError:
+        return True
+
+    return False
+
+
+need_dotenv = pytest.mark.skipif(
+    dotenv_not_available(), reason="dotenv is not installed"
+)
 
 
 @need_dotenv
@@ -530,7 +540,7 @@ def test_dotenv_path(monkeypatch):
 
 
 def test_dotenv_optional(monkeypatch):
-    monkeypatch.setattr("flask.cli.dotenv", None)
+    monkeypatch.setitem(sys.modules, "dotenv", None)
     monkeypatch.chdir(test_path)
     load_dotenv()
     assert "FOO" not in os.environ
@@ -602,7 +612,8 @@ def test_run_cert_import(monkeypatch):
 
 
 def test_run_cert_no_ssl(monkeypatch):
-    monkeypatch.setattr("flask.cli.ssl", None)
+    monkeypatch.setitem(sys.modules, "ssl", None)
+
     with pytest.raises(click.BadParameter):
         run_command.make_context("run", ["--cert", "not_here"])