Implement PEP 708

news/11784.feature.rst

@@ -0,0 +1 @@
+Introduce repository alternate locations and project tracking, as per PEP 708.

src/pip/_internal/exceptions.py

@@ -13,7 +13,7 @@
 import re
 import sys
 from itertools import chain, groupby, repeat
-from typing import TYPE_CHECKING, Dict, Iterator, List, Literal, Optional, Union
+from typing import TYPE_CHECKING, Dict, Iterator, List, Literal, Optional, Set, Union
 
 from pip._vendor.rich.console import Console, ConsoleOptions, RenderResult
 from pip._vendor.rich.markup import escape
@@ -775,3 +775,134 @@ def __init__(self, *, distribution: "BaseDistribution") -> None:
             ),
             hint_stmt=None,
         )
+
+
+class InvalidMultipleRemoteRepositories(DiagnosticPipError):
+    """Common error for issues with multiple remote repositories."""
+
+    reference = "invalid-multiple-remote-repositories"
+    _note_suffix = (
+        "See PEP 708 for the specification. "
+        "You can override this check, which will disable the security "
+        "protection it provides from dependency confusion attacks, "
+        "by passing --insecure-multiple-remote-repositories."
+    )
+
+
+class InvalidTracksUrl(InvalidMultipleRemoteRepositories):
+    """There was an issue with a Tracks metadata url.
+
+    Tracks urls must point to the actual URLs for that project,
+    point to the repositories that own the namespaces, and
+    point to a project with the exact same name (after normalization).
+    """
+
+    reference = "invalid-tracks-url"
+
+    def __init__(
+        self,
+        *,
+        package: str,
+        remote_repositories: Set[str],
+        invalid_tracks: Set[str],
+    ) -> None:
+        super().__init__(
+            kind="error",
+            message=Text(
+                f"One or more Tracks for {escape(package)} "
+                "were not valid. "
+                "The remote repositories are "
+                f"{'; '.join(sorted(escape(r) for r in remote_repositories))}."
+                "The invalid tracks are "
+                f"{'; '.join(sorted(escape(r) for r in invalid_tracks))}."
+            ),
+            context=Text(
+                "Tracks urls must point to the actual URLs for a project, "
+                "point to the repositories that own the namespaces, and "
+                "point to a project with the exact same normalized name."
+            ),
+            hint_stmt=None,
+            note_stmt=Text(
+                "The way to resolve this error is to contact the owners of "
+                "each remote repository, and ask if it makes sense to "
+                "configure them to merge namespaces. " + self._note_suffix
+            ),
+        )
+
+
+class InvalidAlternativeLocationsUrl(InvalidMultipleRemoteRepositories):
+    """The list of Alternate Locations for each repository do not match.
+
+    In order for this metadata to be trusted, there MUST be agreement between
+    all locations where that project is found as to what the alternate locations are.
+    """
+
+    reference = "invalid-alternative-locations"
+
+    def __init__(
+        self,
+        *,
+        package: str,
+        remote_repositories: Set[str],
+        invalid_locations: Set[str],
+    ) -> None:
+        super().__init__(
+            kind="error",
+            message=Text(
+                f"One or more Alternate Locations for {escape(package)} "
+                "were different among the remote repositories. "
+                "The remote repositories are "
+                f"{'; '.join(sorted(escape(r) for r in remote_repositories))}."
+                "The alternate locations not agreed by all remote "
+                "repository are "
+                f"{'; '.join(sorted(escape(r) for r in invalid_locations))}."
+            ),
+            context=Text(
+                "To be able to trust the remote repository Alternate Locations, "
+                "all remote repositories must agree on the list of Locations."
+            ),
+            hint_stmt=None,
+            note_stmt=Text(
+                "The way to resolve this error is to contact the owners of the package "
+                "at each remote repository, and ask if it makes sense to "
+                "configure them to merge namespaces. " + self._note_suffix
+            ),
+        )
+
+
+class UnsafeMultipleRemoteRepositories(InvalidMultipleRemoteRepositories):
+    """More than one remote repository was provided for a package,
+    with no indication that the remote repositories can be safely merged.
+
+    The repositories, packages, or user did not indicate that
+    it is safe to merge remote repositories.
+
+    Multiple remote repositories are not merged by default
+    to reduce the risk of dependency confusion attacks."""
+
+    reference = "unsafe-multiple-remote-repositories"
+
+    def __init__(self, *, package: str, remote_repositories: Set[str]) -> None:
+        super().__init__(
+            kind="error",
+            message=Text(
+                f"More than one remote repository was found for {escape(package)}, "
+                "with no indication that the remote repositories can be safely merged. "
+                "The repositories are "
+                f"{'; '.join(sorted(escape(r) for r in remote_repositories))}."
+            ),
+            context=Text(
+                "Multiple remote repositories are not merged by default "
+                "to reduce the risk of dependency confusion attacks."
+            ),
+            hint_stmt=Text(
+                "Remote repositories can be specified or discovered using "
+                "--index-url, --extra-index-url, and --find-links. "
+                "Please check the pip command to see if these are in use."
+            ),
+            note_stmt=Text(
+                "The way to resolve this error is to contact the remote repositories "
+                "and package owners, and ask if it makes sense to configure them to "
+                "merge namespaces. " + self._note_suffix
+            ),
+        )

src/pip/_internal/index/collector.py

@@ -24,6 +24,7 @@
     Optional,
     Protocol,
     Sequence,
+    Set,
     Tuple,
     Union,
 )
@@ -33,7 +34,12 @@
 from pip._vendor.requests.exceptions import RetryError, SSLError
 
 from pip._internal.exceptions import NetworkConnectionError
-from pip._internal.models.link import Link
+from pip._internal.models.link import (
+    HEAD_META_ALTERNATE_LOCATIONS,
+    HEAD_META_PREFIX,
+    HEAD_META_TRACKS,
+    Link,
+)
 from pip._internal.models.search_scope import SearchScope
 from pip._internal.network.session import PipSession
 from pip._internal.network.utils import raise_for_status
@@ -224,13 +230,22 @@ def wrapper_wrapper(page: "IndexContent") -> List[Link]:
 def parse_links(page: "IndexContent") -> Iterable[Link]:
     """
     Parse a Simple API's Index Content, and yield its anchor elements as Link objects.
+    Includes known metadata from the HTML header.
     """
-
+    url = page.url
     content_type_l = page.content_type.lower()
     if content_type_l.startswith("application/vnd.pypi.simple.v1+json"):
         data = json.loads(page.content)
+        project_track_urls = set(data.get("meta", {}).get("tracks", []))
+        repo_alt_urls = set(data.get("alternate-locations", []))
+        repo_alt_urls.add(page.url)
         for file in data.get("files", []):
-            link = Link.from_json(file, page.url)
+            link = Link.from_json(
+                file,
+                page_url=page.url,
+                project_track_urls=project_track_urls,
+                repo_alt_urls=repo_alt_urls,
+            )
             if link is None:
                 continue
             yield link
@@ -240,10 +255,17 @@ def parse_links(page: "IndexContent") -> Iterable[Link]:
     encoding = page.encoding or "utf-8"
     parser.feed(page.content.decode(encoding))
 
-    url = page.url
     base_url = parser.base_url or url
     for anchor in parser.anchors:
-        link = Link.from_element(anchor, page_url=url, base_url=base_url)
+        repo_alt_urls = parser.repo_alt_urls or set()
+        repo_alt_urls.add(page.url)
+        link = Link.from_element(
+            anchor,
+            page_url=url,
+            base_url=base_url,
+            project_track_urls=parser.project_track_urls,
+            repo_alt_urls=repo_alt_urls,
+        )
         if link is None:
             continue
         yield link
@@ -282,6 +304,8 @@ def __init__(self, url: str) -> None:
         self.url: str = url
         self.base_url: Optional[str] = None
         self.anchors: List[Dict[str, Optional[str]]] = []
+        self.project_track_urls: Set[str] = set()
+        self.repo_alt_urls: Set[str] = set()
 
     def handle_starttag(self, tag: str, attrs: List[Tuple[str, Optional[str]]]) -> None:
         if tag == "base" and self.base_url is None:
@@ -290,13 +314,36 @@ def handle_starttag(self, tag: str, attrs: List[Tuple[str, Optional[str]]]) -> N
                 self.base_url = href
         elif tag == "a":
             self.anchors.append(dict(attrs))
+        elif tag == "meta":
+            meta_attrs = dict(attrs)
+            meta_key = meta_attrs.get("name", "").strip()
+            meta_val = meta_attrs.get("content", "").strip()
+            if meta_key and meta_val:
+                if (
+                    meta_key == self._meta_key_tracks
+                    and meta_val not in self.project_track_urls
+                ):
+                    self.project_track_urls.add(meta_val)
+                elif (
+                    meta_key == self._meta_key_alternate_locations
+                    and meta_val not in self.repo_alt_urls
+                ):
+                    self.repo_alt_urls.add(meta_val)
 
     def get_href(self, attrs: List[Tuple[str, Optional[str]]]) -> Optional[str]:
         for name, value in attrs:
             if name == "href":
                 return value
         return None
 
+    @functools.cached_property
+    def _meta_key_tracks(self) -> str:
+        return f"{HEAD_META_PREFIX}:{HEAD_META_TRACKS}"
+
+    @functools.cached_property
+    def _meta_key_alternate_locations(self) -> str:
+        return f"{HEAD_META_PREFIX}:{HEAD_META_ALTERNATE_LOCATIONS}"
+
 
 def _handle_get_simple_fail(
     link: Link,