Wrap commands in __main__ to prepend 'covimerage: ' prefix with errors.

covimerage/__main__.py

@@ -1,3 +1,26 @@
-if __name__ == '__main__':
+def wrap_for_errormsg(f, *args, **kwargs):
+    try:
+        f(*args, standalone_mode=False, **kwargs)
+    except Exception as exc:
+        from click.exceptions import ClickException
+        if isinstance(exc, ClickException):
+            import sys
+            from click.utils import echo
+
+            msg = 'covimerage: error: %s' % (exc.format_message(),)
+            echo(msg, err=True)
+            sys.exit(2)
+
+
+def main():
     from .cli import main
+    wrap_for_errormsg(main.main, prog_name='covimerage')
+
+
+def run():
+    from .cli import run
+    wrap_for_errormsg(run.main, prog_name='covimerage-run')
+
+
+if __name__ == '__main__':
     main()

setup.py

@@ -74,8 +74,8 @@ def run(self):
     packages=['covimerage'],
     entry_points={
         'console_scripts': [
-            'covimerage=covimerage.cli:main',
-            'covimerage-run=covimerage.cli:run',
+            'covimerage=covimerage.__main__:main',
+            'covimerage-run=covimerage.__main__:run',
         ],
     },
     use_scm_version={

tests/test_cli.py

@@ -15,7 +15,7 @@
 def test_dunder_main_run(capfd):
     assert call([sys.executable, '-m', 'covimerage']) == 0
     out, err = capfd.readouterr()
-    assert out.startswith('Usage: __main__')
+    assert out.startswith('Usage: covimerage')
 
 
 def test_dunder_main_run_help(capfd):