Properly support config_file_path being None

* Prevent error when the config file is a stream, to support `-` as the config.
* Fix type annotations and edge cases when `config_file_path` is None
* Properly prevent users setting `config_file_path` in mkdocs.yml - this was not intended.

docs/user-guide/configuration.md

@@ -1021,6 +1021,12 @@ Therefore, defining paths in a parent file which is inherited by multiple
 different sites may not work as expected. It is generally best to define
 path based options in the primary configuration file only.
 
+The inheritance can also be used as a quick way to override keys on the command line - by using stdin as the config file. For example:
+
+```bash
+echo '{INHERIT: mkdocs.yml, site_name: "Renamed site"}' | mkdocs build -f -
+```
+
 [Theme Developer Guide]: ../dev-guide/themes.md
 [pymdk-extensions]: https://python-markdown.github.io/extensions/
 [pymkd]: https://python-markdown.github.io/

mkdocs/__main__.py

@@ -106,7 +106,9 @@ def __del__(self):
 pass_state = click.make_pass_decorator(State, ensure=True)
 
 clean_help = "Remove old files from the site_dir before building (the default)."
-config_help = "Provide a specific MkDocs config"
+config_help = (
+    "Provide a specific MkDocs config. This can be a file name, or '-' to read from stdin."
+)
 dev_addr_help = "IP address and port to serve documentation locally (default: localhost:8000)"
 strict_help = "Enable strict mode. This will cause MkDocs to abort the build on any warnings."
 theme_help = "The theme to use when building your documentation."

mkdocs/commands/gh_deploy.py

@@ -116,7 +116,7 @@ def gh_deploy(
 
     if message is None:
         message = default_message
-    sha = _get_current_sha(os.path.dirname(config.config_file_path))
+    sha = _get_current_sha(os.path.dirname(config.config_file_path or ''))
     message = message.format(version=mkdocs.__version__, sha=sha)
 
     log.info(

mkdocs/config/base.py

@@ -331,7 +331,10 @@ def _open_config_file(config_file: str | IO | None) -> Iterator[IO]:
     else:
         log.debug(f"Loading configuration file: {result_config_file}")
         # Ensure file descriptor is at beginning
-        result_config_file.seek(0)
+        try:
+            result_config_file.seek(0)
+        except OSError:
+            pass
 
     try:
         yield result_config_file

mkdocs/config/config_options.py

@@ -814,8 +814,7 @@ def run_validation(self, value: object) -> theme.Theme:
 
         # Ensure custom_dir is an absolute path
         if 'custom_dir' in theme_config and not os.path.isabs(theme_config['custom_dir']):
-            assert self.config_file_path is not None
-            config_dir = os.path.dirname(self.config_file_path)
+            config_dir = os.path.dirname(self.config_file_path or '')
             theme_config['custom_dir'] = os.path.join(config_dir, theme_config['custom_dir'])
 
         if 'custom_dir' in theme_config and not os.path.isdir(theme_config['custom_dir']):

mkdocs/config/defaults.py

@@ -16,8 +16,8 @@ def get_schema() -> base.PlainConfigSchema:
 class MkDocsConfig(base.Config):
     """The configuration of MkDocs itself (the root object of mkdocs.yml)."""
 
-    config_file_path: str = c.Optional(c.Type(str))  # type: ignore[assignment]
-    """Reserved for internal use, stores the mkdocs.yml config file."""
+    config_file_path: str | None = c.Optional(c.Type(str))  # type: ignore[assignment]
+    """The path to the mkdocs.yml config file. Can't be populated from the config."""
 
     site_name = c.Type(str)
     """The title to use for the documentation."""
@@ -136,3 +136,8 @@ class MkDocsConfig(base.Config):
 
     watch = c.ListOfPaths(default=[])
     """A list of extra paths to watch while running `mkdocs serve`."""
+
+    def load_dict(self, patch: dict) -> None:
+        super().load_dict(patch)
+        if 'config_file_path' in patch:
+            raise base.ValidationError("Can't set config_file_path in config")

mkdocs/tests/base.py

@@ -23,20 +23,17 @@ def get_markdown_toc(markdown_source):
     return md.toc_tokens
 
 
-def load_config(**cfg) -> MkDocsConfig:
+def load_config(config_file_path: str | None = None, **cfg) -> MkDocsConfig:
     """Helper to build a simple config for testing."""
     path_base = os.path.join(os.path.abspath(os.path.dirname(__file__)), 'integration', 'minimal')
-    cfg = cfg or {}
     if 'site_name' not in cfg:
         cfg['site_name'] = 'Example'
-    if 'config_file_path' not in cfg:
-        cfg['config_file_path'] = os.path.join(path_base, 'mkdocs.yml')
     if 'docs_dir' not in cfg:
         # Point to an actual dir to avoid a 'does not exist' error on validation.
         cfg['docs_dir'] = os.path.join(path_base, 'docs')
     if 'plugins' not in cfg:
         cfg['plugins'] = []
-    conf = MkDocsConfig(config_file_path=cfg['config_file_path'])
+    conf = MkDocsConfig(config_file_path=config_file_path or os.path.join(path_base, 'mkdocs.yml'))
     conf.load_dict(cfg)
 
     errors_warnings = conf.validate()

mkdocs/tests/config/config_tests.py

@@ -218,13 +218,10 @@ def test_theme(self, mytheme, custom):
                 self.assertEqual({k: conf['theme'][k] for k in iter(conf['theme'])}, result['vars'])
 
     def test_empty_nav(self):
-        conf = defaults.MkDocsConfig()
-        conf.load_dict(
-            {
-                'site_name': 'Example',
-                'config_file_path': os.path.join(os.path.abspath('.'), 'mkdocs.yml'),
-            }
+        conf = defaults.MkDocsConfig(
+            config_file_path=os.path.join(os.path.abspath('.'), 'mkdocs.yml')
         )
+        conf.load_dict({'site_name': 'Example'})
         conf.validate()
         self.assertEqual(conf['nav'], None)
 
@@ -242,34 +239,26 @@ def test_error_on_pages(self):
         self.assertEqual(warnings, [])
 
     def test_doc_dir_in_site_dir(self):
-        j = os.path.join
-
         test_configs = (
-            {'docs_dir': j('site', 'docs'), 'site_dir': 'site'},
+            {'docs_dir': os.path.join('site', 'docs'), 'site_dir': 'site'},
             {'docs_dir': 'docs', 'site_dir': '.'},
             {'docs_dir': '.', 'site_dir': '.'},
             {'docs_dir': 'docs', 'site_dir': ''},
             {'docs_dir': '', 'site_dir': ''},
             {'docs_dir': 'docs', 'site_dir': 'docs'},
         )
 
-        cfg = {
-            'config_file_path': j(os.path.abspath('..'), 'mkdocs.yml'),
-        }
-
         for test_config in test_configs:
             with self.subTest(test_config):
-                patch = {**cfg, **test_config}
-
                 # Same as the default schema, but don't verify the docs_dir exists.
                 conf = config.Config(
                     schema=(
                         ('docs_dir', c.Dir(default='docs')),
                         ('site_dir', c.SiteDir(default='site')),
-                        ('config_file_path', c.Type(str)),
-                    )
+                    ),
+                    config_file_path=os.path.join(os.path.abspath('..'), 'mkdocs.yml'),
                 )
-                conf.load_dict(patch)
+                conf.load_dict(test_config)
 
                 errors, warnings = conf.validate()