fix: find retroarch.cfg for any --dest spelling

The config was looked up by the BIOS folder exactly as typed: a relative --dest, a link or another case sent save-folder files to a guessed folder and refused --installed-cores.

install.py

@@ -3993,13 +3993,42 @@ def _retroarch_config_for(bios_path: Path) -> tuple[Path, Path] | None:
     sent Azahar's keys.txt to a guessed folder where line mode read
     savefile_directory, and found no core where line mode found them.
     """
-    found = _RETROARCH_CONFIGS.get(bios_path)
+    found = _retroarch_config_at(bios_path)
     if found is not None or _CONFIGS_READ:
         return found
     _CONFIGS_READ.append(True)
     with contextlib.redirect_stdout(io.StringIO()), contextlib.redirect_stderr(io.StringIO()):
         detect_platforms(_INVOCATION.os_type or detect_os())
-    return _RETROARCH_CONFIGS.get(bios_path)
+    return _retroarch_config_at(bios_path)
+
+
+def _folder_key(path: Path) -> str:
+    """The folder as the system names it: absolute, links followed, and
+    case folded where the system's default filesystem folds it."""
+    real = os.path.realpath(path)
+    return real.casefold() if sys.platform in ("win32", "darwin") else real
+
+
+def _retroarch_config_at(bios_path: Path) -> tuple[Path, Path] | None:
+    """The config detection read for bios_path, however the folder is
+    written: --dest relative, through a link, or in another case. The
+    configs are keyed by the folder as each retroarch.cfg writes it."""
+    found = _RETROARCH_CONFIGS.get(bios_path)
+    if found is not None or not _RETROARCH_CONFIGS:
+        return found
+    wanted = _folder_key(bios_path)
+    for system_dir, config in _RETROARCH_CONFIGS.items():
+        if _folder_key(system_dir) == wanted:
+            return config
+    # A drive whose filesystem folds case where the system's default does
+    # not (or the reverse): the filesystem answers for folders that exist.
+    for system_dir, config in _RETROARCH_CONFIGS.items():
+        try:
+            if os.path.samefile(system_dir, bios_path):
+                return config
+        except (OSError, ValueError):
+            continue
+    return None
 
 
 def save_directory_for(
@@ -11632,7 +11661,7 @@ def _plan_lines(check: dict, dest: Path | None, state: TuiState) -> list:
                  f"{wrong} wrong {'copy' if wrong == 1 else 'copies'}")
     if check is state.check:
         lines += [_styled(line, "path") for line in _saves_lines(state)]
-    found_in = _RETROARCH_CONFIGS.get(dest) if dest is not None else None
+    found_in = _retroarch_config_at(dest) if dest is not None else None
     if found_in:
         lines.append(_styled(f"Named by {_short_path(Path(found_in[0]), state.home)}", "path"))
     free = state.facts.get("free")
@@ -12365,7 +12394,7 @@ def _install_kind(path: Path) -> str:
     """What sets one install of a frontend apart from another of the same."""
     # The config detection read it from says how it was installed: the
     # Flatpak's system directory can be anywhere its config names.
-    found = _RETROARCH_CONFIGS.get(path)
+    found = _retroarch_config_at(path)
     text = path.as_posix() + (" " + Path(found[0]).as_posix() if found else "")
     for marker, word in (("/.var/app/", "Flatpak"), ("/steamapps/", "Steam"),
                          ("/snap/", "Snap")):

tests/test_save_root.py

@@ -25,6 +25,7 @@ import threading
 import unittest
 import zipfile
 from pathlib import Path
+from unittest import mock
 
 REPO_ROOT = Path(__file__).resolve().parent.parent
 sys.path.insert(0, str(REPO_ROOT / "scripts"))
@@ -552,6 +553,60 @@ class TheInstallerFindsTheSaveDirectory(unittest.TestCase):
                                            False, False))
         install._check_save_directory(manifest)
 
+    def other_spelling(self, spelled: Path) -> install.SavePlace | str:
+        """save_directory_for the BIOS folder written another way, the config
+        keyed as detection writes it, with savefile_directory set."""
+        saves = self.root / "MySaves"
+        saves.mkdir(exist_ok=True)
+        self.cfg.write_text(f'savefile_directory = "{saves}"\n')
+        install._RETROARCH_CONFIGS[self.bios] = (self.cfg, self.app)
+        self.addCleanup(install._SAVE_DIRS.pop, spelled, None)
+        with mock.patch.object(install, "_CONFIGS_READ", [True]):
+            return install.save_directory_for(spelled, self.MANIFEST)
+
+    def test_a_relative_bios_folder_finds_its_config(self):
+        """cd ~/.config/retroarch && install.py --dest system: the save files
+        went to a guessed saves/ beside it."""
+        self.addCleanup(os.chdir, os.getcwd())
+        os.chdir(self.app)
+        self.assertEqual(self.other_spelling(Path("system")),
+                         install.SavePlace(self.root / "MySaves", True))
+
+    def test_a_bios_folder_through_a_link_finds_its_config(self):
+        """EmuDeck links RetroArch's system folder to ~/Emulation/bios."""
+        link = self.root / "bios-link"
+        link.symlink_to(self.bios, target_is_directory=True)
+        self.assertEqual(self.other_spelling(link),
+                         install.SavePlace(self.root / "MySaves", True))
+        linked_app = self.root / "RA-link"
+        linked_app.symlink_to(self.app, target_is_directory=True)
+        self.assertEqual(self.other_spelling(linked_app / "system"),
+                         install.SavePlace(self.root / "MySaves", True))
+
+    def test_case_only_differs_where_the_system_folds_it(self):
+        spelled = Path(str(self.bios).upper())
+        with mock.patch.object(install.sys, "platform", "linux"):
+            self.assertNotEqual(self.other_spelling(spelled),
+                                install.SavePlace(self.root / "MySaves", True))
+        install._SAVE_DIRS.pop(spelled, None)
+        with mock.patch.object(install.sys, "platform", "darwin"):
+            self.assertEqual(self.other_spelling(spelled),
+                             install.SavePlace(self.root / "MySaves", True))
+
+    def test_the_cores_folder_through_another_spelling(self):
+        cores = self.root / "MyCores"
+        cores.mkdir()
+        self.cfg.write_text(f'libretro_directory = "{cores}"\n')
+        install._RETROARCH_CONFIGS[self.bios] = (self.cfg, self.app)
+        link = self.root / "bios-link"
+        link.symlink_to(self.bios, target_is_directory=True)
+        self.addCleanup(os.chdir, os.getcwd())
+        os.chdir(self.app)
+        with mock.patch.object(install, "_CONFIGS_READ", [True]):
+            for spelled in (Path("system"), link, Path("./system/")):
+                with self.subTest(spelled=str(spelled)):
+                    self.assertEqual(install.core_dirs("retroarch", spelled), [cores])
+
     def test_the_entry_path(self):
         saves = (self.app / "saves").resolve()
         install._SAVE_DIRS[self.bios] = install.SavePlace(self.app / "saves", True)