Add safe_extra to _normalization

1 files changed, 11 insertions, 0 deletions

diff --git a/setuptools/_normalization.py b/setuptools/_normalization.py
index 31899f7a..3e94e662 100644
--- a/setuptools/_normalization.py
+++ b/setuptools/_normalization.py
@@ -14,6 +14,7 @@ _Path = Union[str, Path]
 # https://packaging.python.org/en/latest/specifications/core-metadata/#name
 _VALID_NAME = re.compile(r"^([A-Z0-9]|[A-Z0-9][A-Z0-9._-]*[A-Z0-9])$", re.I)
 _UNSAFE_NAME_CHARS = re.compile(r"[^A-Z0-9.]+", re.I)
+_NON_ALPHANUMERIC = re.compile(r"[^A-Z0-9]+", re.I)
 
 
 def safe_identifier(name: str) -> str:
@@ -92,6 +93,16 @@ def best_effort_version(version: str) -> str:
         return safe_name(v)
 
 
+def safe_extra(extra: str) -> str:
+    """Normalize extra name according to PEP 685
+    >>> safe_extra("_FrIeNdLy-._.-bArD")
+    'friendly-bard'
+    >>> safe_extra("FrIeNdLy-._.-bArD__._-")
+    'friendly-bard'
+    """
+    return _NON_ALPHANUMERIC.sub("-", extra).strip("-").lower()
+
+
 def filename_component(value: str) -> str:
     """Normalize each component of a filename (e.g. distribution/version part of wheel)
     Note: ``value`` needs to be already normalized.