fix: keep MinUI core dirs out of the tree view

Without --platform, cross_reference and the site's gap report merged every
platform's standalone set, MinUI, NextUI and MyMinUI coredir: markers
included. A marker says which cores one platform hands a folder, so in the
union every core those three do not list got no layout: px68k showed 0 of
6 files and the global report lost 238 profiles and 1201 files.
merged_standalone_set drops the markers, and both readers use it.

scripts/common.py

@@ -2446,6 +2446,22 @@ def standalone_set(config: dict) -> set[str]:
     return names
 
 
+def merged_standalone_set(configs: Iterable[dict]) -> set[str]:
+    """The standalone set of several platforms read as one tree.
+
+    A per-core directory marker says which cores one platform hands a folder
+    and that it hands the others none. Carried into the union, MinUI's 86
+    markers left every core they do not list without a layout: the global
+    gap report lost 238 profiles and 1201 files without a word.
+    """
+    return {
+        tag
+        for config in configs
+        for tag in standalone_set(config)
+        if not tag.startswith(CORE_DIR_PREFIX)
+    }
+
+
 def _handed(standalone_cores: Iterable[str]) -> list:
     """The directories a standalone set carries, as launchers built them."""
     from launchers import HandedDirectory  # noqa: PLC0415

scripts/cross_reference.py

@@ -1156,12 +1156,12 @@ def main() -> None:
         # The tree as every platform runs it: a profile some platform runs
         # standalone keeps its standalone entries. Laid out as libretro only,
         # eka2l1, dolphin and xenia-edge lost 133 files no platform declares.
-        from common import list_registered_platforms
+        from common import list_registered_platforms, merged_standalone_set
 
-        standalone_cores = set().union(*(
-            standalone_set(load_platform_config(name, args.platforms_dir))
+        standalone_cores = merged_standalone_set(
+            load_platform_config(name, args.platforms_dir)
             for name in list_registered_platforms(args.platforms_dir, include_archived=True)
-        ))
+        )
 
     if not profiles:
         if emulator and args.target and emulator in run_anywhere:

scripts/generate_site.py

@@ -1159,7 +1159,7 @@ def build_emulator_gap_report(
         for k, v in profiles.items()
         if v.get("type") not in ("alias", "test")
     }
-    from common import platform_declarations, standalone_set
+    from common import merged_standalone_set, platform_declarations
     from validation import case_folded_slots
 
     # The command line passes these too: without them a RetroBat file named
@@ -1171,8 +1171,8 @@ def build_emulator_gap_report(
     return run_cross_reference(
         unique_profiles, declared, db,
         data_names=data_names, all_declared=all_declared,
-        standalone_cores=set().union(
-            *(standalone_set(cov["config"]) for cov in coverages.values())
+        standalone_cores=merged_standalone_set(
+            cov["config"] for cov in coverages.values()
         ),
         folded_slots=folded,
     )

tests/test_minui_platform.py

@@ -439,5 +439,30 @@ class TheSitePageOfACardPlatform(unittest.TestCase):
         self.assertIn("No ZIP for MinUI. The command installs every file and checks it.", page)
 
 
+class TheWholeTreeKeepsCoresMinUILeavesOut(unittest.TestCase):
+    """Without --platform, cross_reference and the site's gap report merge
+    every platform's standalone set. MinUI's per-core folders came along and
+    left every core MinUI does not list with no layout: px68k showed 0 files
+    and the global report lost 238 profiles."""
+
+    def test_a_core_minui_does_not_list_keeps_its_files(self):
+        from common import merged_standalone_set, platform_layouts
+
+        minui = {"core_system_dirs": {"Bios/FC": {"cores": ["fceumm"]}}}
+        retroarch = {}
+        merged = merged_standalone_set([minui, retroarch])
+        profile = {"type": "libretro", "files": [{"name": "cgrom.tmp"}]}
+        layouts = platform_layouts("px68k", profile, merged)
+        self.assertEqual(layouts, [(profile, False)])
+
+    def test_both_readers_build_the_set_the_same_way(self):
+        for script in ("cross_reference.py", "generate_site.py"):
+            source = (REPO_ROOT / "scripts" / script).read_text(encoding="utf-8")
+            with self.subTest(script=script):
+                self.assertIn("merged_standalone_set(", source)
+                self.assertNotIn("set().union(*(\n            standalone_set(", source)
+                self.assertNotIn("*(standalone_set(cov", source)
+
+
 if __name__ == "__main__":
     unittest.main()