Implement PEP 753 normalization for Home-Page fallback (#13242)

We treat "homepage" as a well-known project URL, using it to replace
the Home-Page core metadata field if it's undefined. This patch updates
the normalization logic to follow PEP 753.

The logic emitting the raw project URLs was left unchanged as we don't
really care for well-known vs. boring URLs here.

Author: ichard26

news/13135.feature.rst

@@ -0,0 +1,3 @@
+Use :pep:`753` "Well-known Project URLs in Metadata" normalization rules when
+identifying an equivalent project URL to replace a missing ``Home-Page`` field
+in ``pip show``.

src/pip/_internal/commands/show.py

@@ -1,4 +1,5 @@
 import logging
+import string
 from optparse import Values
 from typing import Generator, Iterable, Iterator, List, NamedTuple, Optional
 
@@ -13,6 +14,13 @@
 logger = logging.getLogger(__name__)
 
 
+def normalize_project_url_label(label: str) -> str:
+    # This logic is from PEP 753 (Well-known Project URLs in Metadata).
+    chars_to_remove = string.punctuation + string.whitespace
+    removal_map = str.maketrans("", "", chars_to_remove)
+    return label.translate(removal_map).lower()
+
+
 class ShowCommand(Command):
     """
     Show information about one or more installed packages.
@@ -135,13 +143,9 @@ def _get_requiring_packages(current_dist: BaseDistribution) -> Iterator[str]:
         if not homepage:
             # It's common that there is a "homepage" Project-URL, but Home-page
             # remains unset (especially as PEP 621 doesn't surface the field).
-            #
-            # This logic was taken from PyPI's codebase.
             for url in project_urls:
                 url_label, url = url.split(",", maxsplit=1)
-                normalized_label = (
-                    url_label.casefold().replace("-", "").replace("_", "").strip()
-                )
+                normalized_label = normalize_project_url_label(url_label)
                 if normalized_label == "homepage":
                     homepage = url.strip()
                     break

tests/functional/test_show.py

@@ -408,7 +408,8 @@ def test_show_deduplicate_requirements(script: PipTestEnvironment) -> None:
 
 
 @pytest.mark.parametrize(
-    "project_url", ["Home-page", "home-page", "Homepage", "homepage"]
+    "project_url",
+    ["Home-page", "home-page", "Homepage", "homepage", "home_PAGE", "home page"],
 )
 def test_show_populate_homepage_from_project_urls(
     script: PipTestEnvironment, project_url: str