blackd: show default values for options (#3712)

* blackd: show default values for options

Reference: https://click.palletsprojects.com/en/8.1.x/api/#click.Option

* Fix spacing in CHANGES.md

CHANGES.md

@@ -44,6 +44,9 @@
 
 <!-- Changes to blackd -->
 
+- The `blackd` argument parser now shows the default values for options in their help
+  text (#3712)
+
 ### Integrations
 
 <!-- For example, Docker, GitHub Actions, pre-commit, editors -->

src/blackd/__init__.py

@@ -59,9 +59,15 @@ class InvalidVariantHeader(Exception):
 
 @click.command(context_settings={"help_option_names": ["-h", "--help"]})
 @click.option(
-    "--bind-host", type=str, help="Address to bind the server to.", default="localhost"
+    "--bind-host",
+    type=str,
+    help="Address to bind the server to.",
+    default="localhost",
+    show_default=True,
+)
+@click.option(
+    "--bind-port", type=int, help="Port to listen on", default=45484, show_default=True
 )
-@click.option("--bind-port", type=int, help="Port to listen on", default=45484)
 @click.version_option(version=black.__version__)
 def main(bind_host: str, bind_port: int) -> None:
     logging.basicConfig(level=logging.INFO)