fix: replay the builder's held and one-file groups

install.region_drops now skips one-file groups (:file:) and lets no
omitted match displace an installable file, as region.resolve_region_drops
does on the builder side. The property test draws both cases and
compares against the builder.

install.ps1

@@ -12,7 +12,7 @@
 
     $ErrorActionPreference = "Stop"
     $defaultInstallUrl = "https://raw.githubusercontent.com/Abdess/retrobios/main/install.py"
-    $defaultInstallSha256 = "376edf794195d74f21e598854b5f3e90fb1955513835264bc9326ad4d2acf9c9"
+    $defaultInstallSha256 = "973d64627af05b239555ab5a83a8902747b7a742bc1176f1b994cf7ac74774f9"
     $maximumInstallerBytes = 2MB
     $installerExit = 0
     $installer = if ($PSScriptRoot) { Join-Path $PSScriptRoot "install.py" } else { $null }

install.py

@@ -142,6 +142,8 @@ _REGION_PARENT = {
     member: parent for parent, members in REGION_TREE.items() for member in members
 }
 REGIONS = frozenset({WORLD_REGION} | set(REGION_TREE) | set(_REGION_PARENT))
+# Marks a region group named after one file that no system names.
+FILE_GROUP = ":file:"
 MAX_SELECTION_TAGS = 1000
 SELECTION_FIELDS = ("systems", "regions", "region_groups", "region_system_groups")
 # The files cores load for systems the platform does not list (game engines,
@@ -2220,7 +2222,10 @@ def _region_rank(file_regions: set[str], requested: list[str]) -> int:
 
 
 def region_drops(
-    entries: list[dict], requested: list[str], systems: list[str] | None = None
+    entries: list[dict],
+    requested: list[str],
+    systems: list[str] | None = None,
+    held: set[str] | None = None,
 ) -> set[str]:
     """Destinations a region priority list withdraws.
 
@@ -2228,10 +2233,16 @@ def region_drops(
     groups the manifest records. Per group, the best-ranked regional file
     stays. A world file beats unmatched regional ones the code does not search
     before it (`priority`, lower first). When nothing matches and no world
-    file exists, every regional file stays, so a group is never emptied. A file with no region never competes and always stays.
+    file exists, every regional file stays, so a group is never emptied. A
+    file with no region never competes and always stays.
 
     A core extra competes whatever systems are chosen, while a platform's own
     declaration competes only when its system is kept, as in the pack.
+
+    ``held`` names the destinations the manifest can install. A match it
+    lacks never displaces a held file: the American BIOS stays under
+    --region japan when the Japanese one is missing. A group named after a
+    single file (FILE_GROUP) competes with nothing and keeps nothing.
     """
     if not requested:
         return set()
@@ -2253,7 +2264,9 @@ def region_drops(
             groups.setdefault(group, []).append((set(regions), entry["dest"], priority))
     keep: set[str] = set()
     drop: set[str] = set()
-    for members in groups.values():
+    for group_id, members in groups.items():
+        if FILE_GROUP in group_id:
+            continue
         world = {dest for regions, dest, _p in members if WORLD_REGION in regions}
         ranks = {dest: priority for _regions, dest, priority in members}
         regional = [
@@ -2265,12 +2278,19 @@ def region_drops(
         if not regional:
             continue
         matched = [(rank, dest) for rank, dest in regional if rank < len(requested)]
-        if matched:
-            best = min(rank for rank, _dest in matched)
-            keep |= {dest for rank, dest in matched if rank == best}
-            drop |= {dest for _rank, dest in regional}
-        elif world:
-            world_ranks = [ranks[dest] for dest in world]
+        winners, rivals = matched, world
+        if held is not None:
+            winners = [(rank, dest) for rank, dest in matched if dest in held]
+            rivals = world & held
+        if winners:
+            best = min(rank for rank, _dest in winners)
+            keep |= {
+                dest for rank, dest in matched
+                if rank == best or (rank < best and dest not in (held or ()))
+            }
+            drop |= {dest for _rank, dest in regional if dest not in keep}
+        elif rivals:
+            world_ranks = [ranks[dest] for dest in rivals]
             best_world = min(world_ranks) if None not in world_ranks else None
             for _rank, dest in regional:
                 ours = ranks[dest]
@@ -2310,7 +2330,10 @@ def narrow(
         files = _filter_by_target(files, cores)
         omitted = _filter_by_target(omitted, cores)
     if regions:
-        dropped = region_drops(files + omitted, regions, systems)
+        # The builder's held set: what the collection serves. An omission
+        # answers the request but takes no installable file's place.
+        held = {f["dest"] for f in files}
+        dropped = region_drops(files + omitted, regions, systems, held)
         files = [f for f in files if f["dest"] not in dropped]
         omitted = [o for o in omitted if o["dest"] not in dropped]
     if systems:

install.sh

@@ -18,7 +18,7 @@ esac
 TEMP_INSTALLER=""
 TEMP_DIRECTORY=""
 DEFAULT_INSTALL_URL="https://raw.githubusercontent.com/Abdess/retrobios/main/install.py"
-DEFAULT_INSTALL_SHA256="376edf794195d74f21e598854b5f3e90fb1955513835264bc9326ad4d2acf9c9"
+DEFAULT_INSTALL_SHA256="973d64627af05b239555ab5a83a8902747b7a742bc1176f1b994cf7ac74774f9"
 MAX_INSTALLER_BYTES=2097152
 
 cleanup() {

tests/test_install_selection.py

@@ -43,6 +43,7 @@ class OneRegionVocabulary(unittest.TestCase):
         self.assertEqual(install.REGION_ALIASES, region.ALIASES)
         self.assertEqual(install.WORLD_REGION, region.WORLD)
         self.assertEqual(install.REGIONS, region.REGIONS)
+        self.assertEqual(install.FILE_GROUP, region.FILE_GROUP)
 
 
 class TheRegionRuleIsTheBuilders(unittest.TestCase):
@@ -72,26 +73,68 @@ class TheRegionRuleIsTheBuilders(unittest.TestCase):
                     index[dest] = {"regions": regions,
                                    "has_untagged": not regions, "emulators": [],
                                    "priorities": {priority}}
-                groups.setdefault(f"g{g}", []).append((dest, dest))
-                if f"g{g}" not in entries[dest]["region_groups"]:
-                    entries[dest]["region_groups"].append(f"g{g}")
+                # A lone core file no system names gets a group of its own.
+                group = f"g{g}" if rng.random() < 0.85 else f"e{region.FILE_GROUP}{dest}"
+                groups.setdefault(group, []).append((dest, dest))
+                if group not in entries[dest]["region_groups"]:
+                    entries[dest]["region_groups"].append(group)
         for entry in entries.values():
             if not entry["regions"]:
                 del entry["regions"], entry["region_groups"]
                 entry.pop("priority", None)
         requested = rng.sample(["north-america", "europe", "japan", "uk", "canada"],
                                rng.randint(1, 3))
-        return groups, index, list(entries.values()), requested
+        held = {dest for dest in entries if rng.random() < 0.7}
+        return groups, index, list(entries.values()), requested, held
 
     def test_two_thousand_random_platforms(self):
         rng = random.Random(20261010)
         for trial in range(2000):
-            groups, index, entries, requested = self._case(rng)
+            groups, index, entries, requested, held = self._case(rng)
             with self.subTest(trial=trial):
                 self.assertEqual(
                     install.region_drops(entries, requested),
                     region.resolve_region_drops(groups, index, requested),
                 )
+                self.assertEqual(
+                    install.region_drops(entries, requested, held=held),
+                    region.resolve_region_drops(groups, index, requested, held),
+                )
+
+    def test_narrow_passes_the_installable_files_as_held(self):
+        """The builder passes what the collection holds (generate_pack
+        _select_variants). An omission is the installer's unheld file."""
+        rng = random.Random(20261021)
+        for trial in range(500):
+            groups, index, entries, requested, held = self._case(rng)
+            files = [dict(e, size=1, cores=None) for e in entries if e["dest"] in held]
+            omitted = [dict(e, cores=None) for e in entries if e["dest"] not in held]
+            kept, still_omitted = install.narrow(files, omitted, [], [], requested)
+            drops = region.resolve_region_drops(groups, index, requested, held)
+            with self.subTest(trial=trial):
+                self.assertEqual(
+                    {f["dest"] for f in kept},
+                    {f["dest"] for f in files} - drops,
+                )
+                self.assertEqual(
+                    {o["dest"] for o in still_omitted},
+                    {o["dest"] for o in omitted} - drops,
+                )
+
+    def test_a_lone_core_file_leaves_its_systems_drop(self):
+        """Dolphin's GC/EUR/IPL.bin is a core extra no system names, plus the
+        GameCube's own declaration. The builder skips the one-file group, so
+        --region us drops it."""
+        entries = [
+            {"dest": "GC/USA/IPL.bin", "regions": ["north-america"],
+             "region_system_groups": ["nintendo-gamecube"]},
+            {"dest": "GC/EUR/IPL.bin", "regions": ["europe"],
+             "region_groups": [f"dolphin{region.FILE_GROUP}GC/EUR/IPL.bin"],
+             "region_system_groups": ["nintendo-gamecube"]},
+        ]
+        self.assertEqual(
+            install.region_drops(entries, ["north-america"]), {"GC/EUR/IPL.bin"}
+        )
 
 
 class Narrowing(unittest.TestCase):
@@ -138,12 +181,21 @@ class Narrowing(unittest.TestCase):
         self.assertIn("scph5501.bin", files)
         self.assertEqual(omitted, [])
 
-    def test_an_unavailable_match_still_wins_as_the_builder_counts_it(self):
+    def test_an_unavailable_match_never_displaces_a_held_file(self):
+        """The builder keeps the held BIOS when the requested one is missing
+        (region.resolve_region_drops, held). The missing one stays reported."""
         files, omitted = self._dests([], [], ["europe"])
-        self.assertNotIn("scph5500.bin", files)
-        self.assertNotIn("scph5501.bin", files)
+        self.assertIn("scph5500.bin", files)
+        self.assertIn("scph5501.bin", files)
         self.assertEqual(omitted, ["scph5502.bin"])
 
+    def test_a_missing_japanese_bios_keeps_the_american_one(self):
+        files = [dict(self.FILES[1])]
+        omitted = [dict(self.OMITTED[0], dest="scph5500.bin", regions=["japan"])]
+        kept, still = install.narrow(files, omitted, [], [], ["japan"])
+        self.assertEqual([f["dest"] for f in kept], ["scph5501.bin"])
+        self.assertEqual([o["dest"] for o in still], ["scph5500.bin"])
+
     def test_no_match_keeps_every_regional_file(self):
         files, _ = self._dests([], [], ["brazil"])
         self.assertIn("scph5500.bin", files)