network: Limit checks to newest versions in slot

Limit network checks to the newest live and non-live versions of every
slot of a package.  This uses a new LatestVersionRepoSource that is
similar to LatestVersionsFilter, except that it is simpler and it
actually works for network checks.

Closes: #391
Signed-off-by: Michał Górny <mgorny@gentoo.org>

Author: mgorny

src/pkgcheck/checks/network.py

@@ -98,6 +98,8 @@ class RequestError(_RequestException):
 class _UrlCheck(NetworkCheck):
     """Generic URL verification check requiring network support."""
 
+    _source = sources.LatestVersionRepoSource
+
     known_results = frozenset([
         DeadUrl, RedirectedUrl, HttpsUrlAvailable, SSLCertificateError,
     ])

src/pkgcheck/sources.py

@@ -4,6 +4,7 @@
 from collections import defaultdict, deque
 from collections.abc import Set
 from dataclasses import dataclass
+from itertools import groupby
 from operator import attrgetter
 
 from pkgcore.ebuild.profiles import ProfileError
@@ -59,6 +60,16 @@ def itermatch(self, restrict, sorter=sorted, **kwargs):
         return self.source.itermatch(restrict, sorter=sorter, **kwargs)
 
 
+class LatestVersionRepoSource(RepoSource):
+    """Repo source that returns only the latest non-VCS and VCS slots"""
+
+    def itermatch(self, *args, **kwargs):
+        for _, pkgs in groupby(super().itermatch(*args, **kwargs),
+                               key=lambda pkg: pkg.slotted_atom):
+            best_by_live = {pkg.live: pkg for pkg in pkgs}
+            yield from sorted(best_by_live.values())
+
+
 class LatestVersionsFilter:
     """Filter source packages, yielding those from the latest non-VCS and VCS slots."""