fix: read the mirror of a gone source

select_views stopped on the first repository that answered as gone, so
yuzu's source_mirror was never read and the profile stayed unchecked. A
gone repository is now passed over, and a profile declared gone that
answers only through its mirror is not reported as a contradiction.

scripts/profile_sync.py

@@ -1107,6 +1107,7 @@ def select_views(
     """
     views: list[RepoView] = []
     seen: set[tuple[str, str]] = set()
+    gone = False
     # A port living on a branch of a fork is absent from the default tip, so
     # the branch it was read from is followed when the profile names one.
     declared = str(profile.get("source_branch") or "") or None
@@ -1121,21 +1122,29 @@ def select_views(
         pin_field = "source" if field == "source_mirror" else field
         branch = declared if pin_field == "source" else None
         head = None
-        for candidate in branch_candidates(url):
-            head = upstream.resolve_head(repo, cache_dir, offline, candidate)
-            if head:
-                branch = candidate
-                break
-        pin, origin = resolve_pin(
-            profile, repo, cache_dir, offline, pin_field, mode, branch
-        )
-        if not pin:
+        try:
+            for candidate in branch_candidates(url):
+                head = upstream.resolve_head(repo, cache_dir, offline, candidate)
+                if head:
+                    branch = candidate
+                    break
+            pin, origin = resolve_pin(
+                profile, repo, cache_dir, offline, pin_field, mode, branch
+            )
+            if not pin:
+                continue
+            head = head or upstream.resolve_head(repo, cache_dir, offline, branch)
+        except upstream.GoneError:
+            # yuzu's source answers 451: the mirror declared after it is what
+            # keeps the profile checkable, so a gone repository is passed over.
+            gone = True
             continue
-        head = head or upstream.resolve_head(repo, cache_dir, offline, branch)
         if not head:
             continue
         seen.add((repo.host, repo.slug))
         views.append(RepoView(repo, pin, head, origin, field))
+    if gone and not views:
+        raise upstream.GoneError(f"{profile.get('emulator', '?')}: every declared repository is gone")
     views = _follow_fork_base(_follow_submodule(views, cache_dir, offline), cache_dir, offline)
     return _hold_upstream(profile, views)
 
@@ -1583,7 +1592,7 @@ def build_report(
             report.skipped = f"upstream gone (declared): {stated_gone}"
             return report
         raise
-    if stated_gone and views:
+    if stated_gone and any(view.field != "source_mirror" for view in views):
         # Declared dead, yet it answered. A profile that keeps saying so stops
         # being read, so the contradiction is the finding.
         report.skipped = (

tests/test_profile_sync.py

@@ -4912,6 +4912,32 @@ class UpstreamVendoredAsASubmodule(unittest.TestCase):
         self.assertEqual(views[1].head, "nesbox-tip")
 
 
+class AMirrorOutlivesAGoneSource(unittest.TestCase):
+    """yuzu's source answers 451. select_views stopped on it and never read
+    the source_mirror declared after it, so the profile stayed unchecked."""
+
+    def test_the_mirror_is_read_when_the_source_is_gone(self):
+        from unittest import mock  # noqa: PLC0415
+
+        gone_repo = profile_sync.upstream.make_repo("github.com", "yuzu-emu-mirror", "yuzu")
+        mirror = profile_sync.upstream.make_repo("github.com", "fork", "yuzu")
+
+        def head(repo, cache_dir, offline=False, branch=None):
+            if repo == gone_repo:
+                raise profile_sync.upstream.GoneError("HTTP 451")
+            return "mirror-head"
+
+        profile = {
+            "source": "https://github.com/yuzu-emu-mirror/yuzu",
+            "source_mirror": "https://github.com/fork/yuzu",
+            "source_commit": "pin",
+        }
+        with mock.patch.object(profile_sync.upstream, "resolve_head", side_effect=head), \
+                mock.patch.object(profile_sync, "resolve_pin", return_value=("pin", "source_commit")):
+            views = profile_sync.select_views(profile, "cache", True)
+        self.assertEqual([(v.repo, v.field) for v in views], [(mirror, "source_mirror")])
+
+
 class AHeldUpstreamStaysOnItsPin(unittest.TestCase):
     """aps3e vendors RPCS3 1f080485 and yaps2 PCSX2 342db515: a bump moved
     upstream_commit to the upstream HEAD neither port carries."""