don't require ssl module for flask cli

CHANGES.rst

@@ -68,6 +68,9 @@ Unreleased
     supported. :issue:`3214`
 -   ``flask.testing.make_test_environ_builder()`` has been deprecated in
     favour of a new class ``flask.testing.EnvironBuilder``. :pr:`3232`
+-   The ``flask run`` command no longer fails if Python is not built
+    with SSL support. Using the ``--cert`` option will show an
+    appropriate error message. :issue:`3211`
 
 .. _#2935: https://github.com/pallets/flask/issues/2935
 .. _#2957: https://github.com/pallets/flask/issues/2957

flask/cli.py

@@ -16,7 +16,6 @@ import inspect
 import os
 import platform
 import re
-import ssl
 import sys
 import traceback
 from functools import update_wrapper
@@ -36,6 +35,11 @@ try:
 except ImportError:
     dotenv = None
 
+try:
+    import ssl
+except ImportError:
+    ssl = None
+
 
 class NoAppException(click.UsageError):
     """Raised if an application cannot be found or loaded."""
@@ -684,6 +688,13 @@ 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:
+            raise click.BadParameter(
+                'Using "--cert" requires Python to be compiled with SSL support.',
+                ctx,
+                param,
+            )
+
         try:
             return self.path_type(value, param, ctx)
         except click.BadParameter:

tests/test_cli.py

@@ -611,6 +611,12 @@ def test_run_cert_import(monkeypatch):
         run_command.make_context("run", ["--cert", "ssl_context", "--key", __file__])
 
 
+def test_run_cert_no_ssl(monkeypatch):
+    monkeypatch.setattr("flask.cli.ssl", None)
+    with pytest.raises(click.BadParameter):
+        run_command.make_context("run", ["--cert", "not_here"])
+
+
 def test_cli_blueprints(app):
     """Test blueprint commands register correctly to the application"""
     custom = Blueprint("custom", __name__, cli_group="customized")