fix: name the split directory by the pack stem

The prefix was assembled by hand and kept a '/' or ':' the full pack
name makes safe (finding 17).

scripts/generate_pack.py

@@ -1919,7 +1919,6 @@ def generate_split_packs(
 ) -> list[str]:
     """Generate split packs (one ZIP per system or manufacturer)."""
     config = load_platform_config(platform_name, platforms_dir)
-    platform_display = config.get("platform", platform_name)
     # The split directory carries the same tags as the packs inside it, or two
     # differently narrowed runs write into one another.
     split_tags = "".join(
@@ -1935,9 +1934,11 @@ def generate_split_packs(
     # The parts carry the version, so the directory does too: a rescrape that
     # moves the version would otherwise leave the old parts beside the new
     # under one SHA256SUMS.txt.
-    version = config.get("version", config.get("dat_version", ""))
-    ver_tag = f"_{version.replace(' ', '')}" if version else ""
-    part_prefix = f"{platform_display.replace(' ', '_')}{ver_tag}{split_tags}"
+    # Named by the stem the full pack reads: assembled here by hand, a '/' in
+    # a version nested the directory where the check never looked for it.
+    part_prefix = (
+        f"{_platform_pack_stem([platform_name], platform_name, platforms_dir)}{split_tags}"
+    )
     split_dir = os.path.join(output_dir, f"{part_prefix}{group_tag}_Split")
     os.makedirs(split_dir, exist_ok=True)
 

tests/test_target_verify.py

@@ -10,6 +10,7 @@ out of a targeted --all run, and the check refuses it as the build does.
 
 from __future__ import annotations
 
+import os
 import sys
 import contextlib
 import io
@@ -196,5 +197,29 @@ class APlatformWithoutTheSystemIsOutOfScope(unittest.TestCase):
         self.assertEqual(ctx.exception.code, 1)
 
 
+class TheSplitDirectoryReadsThePackStem(unittest.TestCase):
+    """The split prefix was assembled by hand: a version 'release/1.22' made
+    'RetroArch_release/1.22_Split', a nested directory the check never
+    found, beside a full pack named 'RetroArch_release-1.22_BIOS_Pack.zip'."""
+
+    def test_a_reserved_character_is_made_safe_as_in_the_full_pack(self):
+        from unittest import mock
+
+        import generate_pack
+
+        config = {"platform": "Foo: Bar", "version": "release/1.22", "systems": {}}
+        with tempfile.TemporaryDirectory(dir=REPO_ROOT / "tmp") as out, \
+                mock.patch.object(generate_pack, "load_platform_config",
+                                  return_value=config), \
+                mock.patch.object(generate_pack, "_collect_emulator_extras",
+                                  return_value=[]):
+            generate_pack.generate_split_packs(
+                "foo", "platforms", {"files": {}}, "bios", out, emu_profiles={},
+            )
+            stem = generate_pack._platform_pack_stem(["foo"], "foo", "platforms")
+            self.assertEqual(os.listdir(out), [f"{stem}_Split"])
+        self.assertEqual(stem, "Foo-_Bar_release-1.22")
+
+
 if __name__ == "__main__":
     unittest.main()