feat: empty config-file triggers default behavior

action.yml

@@ -12,7 +12,7 @@ inputs:
   config-file:
     description: 'File containing the config, defaults to {package}/pyproject.toml'
     required: false
-    default: '{package}/pyproject.toml'
+    default: ''
 branding:
   icon: package
   color: yellow

cibuildwheel/__main__.py

@@ -63,8 +63,8 @@ def main() -> None:
     parser.add_argument(
         "--config-file",
         help="""
-            TOML config file for cibuildwheel. Defaults to pyproject.toml, but
-            can be overridden with this option.
+            TOML config file for cibuildwheel. If empty, this will use
+            pyproject.toml if present, but can be overridden with this option.
         """,
     )
 

cibuildwheel/options.py

@@ -42,7 +42,7 @@ class CommandLineArguments:
     platform: Literal["auto", "linux", "macos", "windows"]
     archs: Optional[str]
     output_dir: Optional[str]
-    config_file: Optional[str]
+    config_file: str
     package_dir: str
     print_build_identifiers: bool
     allow_empty: bool
@@ -335,8 +335,9 @@ def __init__(self, platform: PlatformName, command_line_arguments: CommandLineAr
     def config_file_path(self) -> Optional[Path]:
         args = self.command_line_arguments
 
-        if args.config_file is not None:
+        if args.config_file:
             return Path(args.config_file.format(package=args.package_dir))
+
         # return pyproject.toml, if it's available
         pyproject_toml_path = Path(args.package_dir) / "pyproject.toml"
         if pyproject_toml_path.exists():