Make sure we don't override existing filters

We also need to rename the `title` filter because we were overriding the
jinja2 built-in filter with the same name.

Signed-off-by: Leandro Lucarella <[email protected]>

Author: llucax

cookiecutter/cookiecutter.json

@@ -9,7 +9,7 @@
   ],
   "name": null,
   "description": null,
-  "title": "{{cookiecutter | title}}",
+  "title": "{{cookiecutter | proj_title}}",
   "keywords": "(comma separated: 'frequenz', <type> and <name> are included automatically)",
   "github_org": "frequenz-floss",
   "license": [

cookiecutter/local_extensions.py

@@ -59,6 +59,8 @@ def _register_filters(self) -> None:
             and name.endswith(self._FILTER_SUFFIX)
         ]
         for filer_name in filters:
+            if filer_name in self.environment.filters:
+                raise ValueError(f"Filter {filer_name!r} already registered")
             attr_name = f"{self._FILTER_PREFIX}{filer_name}{self._FILTER_SUFFIX}"
             self.environment.filters[filer_name] = getattr(self, attr_name)
 
@@ -139,7 +141,7 @@ def _github_repo_name_filter(self, cookiecutter: dict[str, str]) -> str:
         end = "-python" if cookiecutter["type"] == "lib" else ""
         return f"{pypi}{end}"
 
-    def _title_filter(self, cookiecutter: dict[str, str]) -> str:
+    def _proj_title_filter(self, cookiecutter: dict[str, str]) -> str:
         """Build a default mkdocs site name for the project.
 
         Args: