Merge link_hash back into _hashes

Commit bad03ef931 introduced the new
link_hash attribute that holds the link's hash info, but that attribute
does the same thing as _hashes, and some existing usages still populate
that old attribute. Since the plural variant covers more use cases (a
file can be hashed with multiple algorithms), we restore the old logic
that uses _hashes before the commit, and consolidate link_hash back into
that attribute.

src/pip/_internal/models/link.py

@@ -79,6 +79,9 @@ class LinkHash:
         name, value = match.groups()
         return cls(name=name, value=value)
 
+    def as_dict(self) -> Dict[str, str]:
+        return {self.name: self.value}
+
     def as_hashes(self) -> Hashes:
         """Return a Hashes instance which checks only for the current hash."""
         return Hashes({self.name: [self.value]})
@@ -165,7 +168,6 @@ class Link(KeyBasedCompareMixin):
         "requires_python",
         "yanked_reason",
         "dist_info_metadata",
-        "link_hash",
         "cache_link_parsing",
         "egg_fragment",
     ]
@@ -177,7 +179,6 @@ class Link(KeyBasedCompareMixin):
         requires_python: Optional[str] = None,
         yanked_reason: Optional[str] = None,
         dist_info_metadata: Optional[str] = None,
-        link_hash: Optional[LinkHash] = None,
         cache_link_parsing: bool = True,
         hashes: Optional[Mapping[str, str]] = None,
     ) -> None:
@@ -200,16 +201,11 @@ class Link(KeyBasedCompareMixin):
             attribute, if present, in a simple repository HTML link. This may be parsed
             into its own `Link` by `self.metadata_link()`. See PEP 658 for more
             information and the specification.
-        :param link_hash: a checksum for the content the link points to. If not
-            provided, this will be extracted from the link URL, if the URL has
-            any checksum.
         :param cache_link_parsing: A flag that is used elsewhere to determine
-                                   whether resources retrieved from this link
-                                   should be cached. PyPI index urls should
-                                   generally have this set to False, for
-                                   example.
+            whether resources retrieved from this link should be cached. PyPI
+            URLs should generally have this set to False, for example.
         :param hashes: A mapping of hash names to digests to allow us to
-                       determine the validity of a download.
+            determine the validity of a download.
         """
 
         # url can be a UNC windows share
@@ -220,13 +216,18 @@ class Link(KeyBasedCompareMixin):
         # Store the url as a private attribute to prevent accidentally
         # trying to set a new value.
         self._url = url
-        self._hashes = hashes if hashes is not None else {}
+
+        link_hash = LinkHash.split_hash_name_and_value(url)
+        hashes_from_link = {} if link_hash is None else link_hash.as_dict()
+        if hashes is None:
+            self._hashes = hashes_from_link
+        else:
+            self._hashes = {**hashes, **hashes_from_link}
 
         self.comes_from = comes_from
         self.requires_python = requires_python if requires_python else None
         self.yanked_reason = yanked_reason
         self.dist_info_metadata = dist_info_metadata
-        self.link_hash = link_hash or LinkHash.split_hash_name_and_value(self._url)
 
         super().__init__(key=url, defining_class=Link)
 
@@ -401,29 +402,26 @@ class Link(KeyBasedCompareMixin):
         if self.dist_info_metadata is None:
             return None
         metadata_url = f"{self.url_without_fragment}.metadata"
-        link_hash: Optional[LinkHash] = None
         # If data-dist-info-metadata="true" is set, then the metadata file exists,
         # but there is no information about its checksum or anything else.
         if self.dist_info_metadata != "true":
             link_hash = LinkHash.split_hash_name_and_value(self.dist_info_metadata)
-        return Link(metadata_url, link_hash=link_hash)
+        else:
+            link_hash = None
+        if link_hash is None:
+            return Link(metadata_url)
+        return Link(metadata_url, hashes=link_hash.as_dict())
 
-    def as_hashes(self) -> Optional[Hashes]:
-        if self.link_hash is not None:
-            return self.link_hash.as_hashes()
-        return None
+    def as_hashes(self) -> Hashes:
+        return Hashes({k: [v] for k, v in self._hashes.items()})
 
     @property
     def hash(self) -> Optional[str]:
-        if self.link_hash is not None:
-            return self.link_hash.value
-        return None
+        return next(iter(self._hashes.values()), None)
 
     @property
     def hash_name(self) -> Optional[str]:
-        if self.link_hash is not None:
-            return self.link_hash.name
-        return None
+        return next(iter(self._hashes), None)
 
     @property
     def show_url(self) -> str:
@@ -452,15 +450,15 @@ class Link(KeyBasedCompareMixin):
 
     @property
     def has_hash(self) -> bool:
-        return self.link_hash is not None
+        return bool(self._hashes)
 
     def is_hash_allowed(self, hashes: Optional[Hashes]) -> bool:
         """
         Return True if the link has a hash and it is allowed by `hashes`.
         """
-        if self.link_hash is None:
+        if hashes is None:
             return False
-        return self.link_hash.is_hash_allowed(hashes)
+        return any(hashes.is_hash_allowed(k, v) for k, v in self._hashes.items())
 
 
 class _CleanResult(NamedTuple):

tests/unit/test_collector.py

@@ -6,7 +6,7 @@ import re
 import uuid
 from pathlib import Path
 from textwrap import dedent
-from typing import List, Optional, Tuple
+from typing import Dict, List, Optional, Tuple
 from unittest import mock
 
 import pytest
@@ -538,7 +538,7 @@ def test_parse_links_json() -> None:
         metadata_link.url
         == "https://example.com/files/holygrail-1.0-py3-none-any.whl.metadata"
     )
-    assert metadata_link.link_hash == LinkHash("sha512", "aabdd41")
+    assert metadata_link._hashes == {"sha512": "aabdd41"}
 
 
 @pytest.mark.parametrize(
@@ -575,41 +575,41 @@ _pkg1_requirement = Requirement("pkg1==1.0")
 
 
 @pytest.mark.parametrize(
-    "anchor_html, expected, link_hash",
+    "anchor_html, expected, hashes",
     [
         # Test not present.
         (
             '<a href="/pkg1-1.0.tar.gz"></a>',
             None,
-            None,
+            {},
         ),
         # Test with value "true".
         (
             '<a href="/pkg1-1.0.tar.gz" data-dist-info-metadata="true"></a>',
             "true",
-            None,
+            {},
         ),
         # Test with a provided hash value.
         (
             '<a href="/pkg1-1.0.tar.gz" data-dist-info-metadata="sha256=aa113592bbe"></a>',  # noqa: E501
             "sha256=aa113592bbe",
-            None,
+            {},
         ),
         # Test with a provided hash value for both the requirement as well as metadata.
         (
             '<a href="/pkg1-1.0.tar.gz#sha512=abc132409cb" data-dist-info-metadata="sha256=aa113592bbe"></a>',  # noqa: E501
             "sha256=aa113592bbe",
-            LinkHash("sha512", "abc132409cb"),
+            {"sha512": "abc132409cb"},
         ),
     ],
 )
 def test_parse_links__dist_info_metadata(
     anchor_html: str,
     expected: Optional[str],
-    link_hash: Optional[LinkHash],
+    hashes: Dict[str, str],
 ) -> None:
     link = _test_parse_links_data_attribute(anchor_html, "dist_info_metadata", expected)
-    assert link.link_hash == link_hash
+    assert link._hashes == hashes
 
 
 def test_parse_links_caches_same_page_by_url() -> None: