fix: reach the Windows side from WSL

Windows rules ran under WSL with C:\ paths read as relative and no Windows variables, so nothing was found and a forced RetroBat install went to ~/bios inside the distribution.

install.ps1

@@ -8,7 +8,7 @@ param(
 
 $ErrorActionPreference = "Stop"
 $defaultInstallUrl = "https://raw.githubusercontent.com/Abdess/retrobios/main/install.py"
-$defaultInstallSha256 = "d86244b95c49d37d3950e0547fe13fa6df589dc21ba9868d46da4ab305522b3f"
+$defaultInstallSha256 = "142edea98e646ed11e27052d3dd02125a27d4cdb7ee04392e6af8fcd28f9762f"
 $maximumInstallerBytes = 2MB
 $installerExit = 0
 $installer = if ($PSScriptRoot) { Join-Path $PSScriptRoot "install.py" } else { $null }

install.py

@@ -26,6 +26,7 @@ import platform
 import re
 import shutil
 import stat
+import subprocess
 import sys
 import tarfile
 import tempfile
@@ -181,9 +182,16 @@ def _os_default_dests(os_type: str) -> dict[str, Path]:
         return {
             # RetroArch's system directory defaults to <exe folder>\system
             # (platform_win32.c), and its installer to C:\RetroArch-Win64.
-            "retroarch": Path("C:/RetroArch-Win64/system"),
+            "retroarch": _host_path("C:/RetroArch-Win64/system"),
             # RetroBat's installer defaults to C:\RetroBat (installer.iss).
-            "retrobat": Path("C:/RetroBat/bios"),
+            "retrobat": _host_path("C:/RetroBat/bios"),
+        }
+    if os_type == "wsl":
+        # RetroArch may be the Linux one inside the distribution; RetroBat
+        # only exists on the Windows side, reached through /mnt/c.
+        return {
+            "retroarch": home / ".config" / "retroarch" / "system",
+            "retrobat": _host_path("C:/RetroBat/bios"),
         }
     if os_type == "darwin":
         return {"retroarch": _macos_retroarch_base() / "system"}
@@ -435,6 +443,42 @@ def _parse_os_release() -> dict[str, str]:
     return result
 
 
+# Set under WSL: a Windows path read from a config or a rule names a drive
+# that Linux sees under /mnt (drvfs). C:\\RetroBat\\bios was used as a relative
+# path and nothing Windows-side was ever found from WSL.
+_WSL = {"active": False, "root": "/mnt"}
+_WINDOWS_VARIABLES = ("USERPROFILE", "APPDATA", "LOCALAPPDATA", "ProgramFiles", "ProgramFiles(x86)")
+
+
+def _host_path(text: str) -> Path:
+    """A path as this machine opens it: under WSL, C:\\X is /mnt/c/X."""
+    match = re.match(r"^([A-Za-z]):(?:[\\/]+(.*))?$", text) if _WSL["active"] else None
+    if match:
+        rest = [part for part in re.split(r"[\\/]", match.group(2) or "") if part]
+        return Path(_WSL["root"], match.group(1).lower(), *rest)
+    return Path(text)
+
+
+def _enter_wsl() -> None:
+    """Read Windows paths through drvfs, and the Windows variables detection
+    needs, which WSL does not pass to Linux (only those named in WSLENV)."""
+    _WSL["active"] = True
+    for variable in _WINDOWS_VARIABLES:
+        if os.environ.get(variable):
+            continue
+        try:
+            result = subprocess.run(
+                ["cmd.exe", "/c", f"echo %{variable}%"],
+                capture_output=True, text=True, timeout=10,
+                cwd="/mnt/c" if Path("/mnt/c").is_dir() else None,
+            )
+        except (OSError, subprocess.SubprocessError):
+            return
+        value = result.stdout.strip()
+        if value and not value.startswith("%"):
+            os.environ[variable] = str(_host_path(value))
+
+
 def _expand_retroarch_path(value: str, app_dir: Path) -> Path:
     """Expand the notations RetroArch writes into its config values.
 
@@ -446,7 +490,7 @@ def _expand_retroarch_path(value: str, app_dir: Path) -> Path:
         return Path(str(Path.home())) / value[2:]
     if value[:1] == ":":
         return app_dir / value[2:]
-    return Path(os.path.expandvars(os.path.expanduser(value)))
+    return _host_path(os.path.expandvars(os.path.expanduser(value)))
 
 
 def _retroarch_cfg_dir(
@@ -506,7 +550,7 @@ def _windows_retroarch_dirs() -> list[Path]:
     names under Program Files, every Steam library, and the Emulators folder
     of an installed ES-DE (es_find_rules.xml lists all of them).
     """
-    candidates = [Path("C:/RetroArch-Win64"), Path("C:/RetroArch")]
+    candidates = [_host_path("C:/RetroArch-Win64"), _host_path("C:/RetroArch")]
     for var in ("ProgramFiles", "ProgramFiles(x86)"):
         root = os.environ.get(var, "")
         if root:
@@ -960,7 +1004,7 @@ def _rule_path(template: str) -> Path:
         if template.startswith(variable):
             rest = [part for part in re.split(r"[\\/]", template[len(variable):]) if part]
             return base.joinpath(*rest)
-    return Path(template)
+    return _host_path(template)
 
 
 # The registry's executable rules: (os, platform, glob under $HOME or
@@ -3501,6 +3545,8 @@ def _install(args: argparse.Namespace, real_stdout: TextIO) -> None:
     print(f"{term.bold('RetroBIOS')} {term.dim(installer_id())}\n")
 
     os_type = detect_os()
+    if os_type == "wsl":
+        _enter_wsl()
 
     # Early exit for listing
     if args.list_platforms:

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="d86244b95c49d37d3950e0547fe13fa6df589dc21ba9868d46da4ab305522b3f"
+DEFAULT_INSTALL_SHA256="142edea98e646ed11e27052d3dd02125a27d4cdb7ee04392e6af8fcd28f9762f"
 MAX_INSTALLER_BYTES=2097152
 
 cleanup() {

tests/test_install.py

@@ -2786,5 +2786,45 @@ class APartialIsClosedBeforeItIsDeleted(unittest.TestCase):
         self.assertLess(branch.index("partial.close()"), branch.index("tmp_path.unlink()"))
 
 
+class WindowsSeenFromWsl(unittest.TestCase):
+    """Under WSL, C:\\RetroBat\\bios was a relative path, %APPDATA% and
+    %USERPROFILE% were unset, and --platform retrobat wrote 7 753 files into
+    ~/bios inside the distribution, where RetroBat reads nothing."""
+
+    def setUp(self):
+        self.root = Path(_tempdir(self))
+        patcher = unittest.mock.patch.dict(install._WSL, {"active": True, "root": str(self.root)})
+        patcher.start()
+        self.addCleanup(patcher.stop)
+
+    def test_a_drive_path_is_its_mount(self):
+        self.assertEqual(install._host_path("C:\\RetroBat\\bios"), self.root / "c" / "RetroBat" / "bios")
+        self.assertEqual(install._rule_path("C:\\RetroBat\\bios"), self.root / "c" / "RetroBat" / "bios")
+        self.assertEqual(install._default_dest("wsl", "retrobat"), self.root / "c" / "RetroBat" / "bios")
+        self.assertEqual(install._host_path("relative/path"), Path("relative/path"))
+
+    def test_retrobat_on_the_windows_side_is_detected(self):
+        (self.root / "c" / "RetroBat" / "bios").mkdir(parents=True)
+        found: list = []
+        install._detect_by_path("wsl", found)
+        self.assertIn(("retrobat", self.root / "c" / "RetroBat" / "bios"), found)
+
+    def test_the_windows_variables_are_read_through_cmd(self):
+        answers = {"USERPROFILE": "C:\\Users\\me", "APPDATA": "C:\\Users\\me\\AppData\\Roaming"}
+
+        def cmd(argv, **_kwargs):
+            name = argv[-1].split("%")[1]
+            return subprocess.CompletedProcess(argv, 0, answers.get(name, f"%{name}%") + "\r\n", "")
+
+        cleared = {name: "" for name in install._WINDOWS_VARIABLES}
+        with unittest.mock.patch.dict(os.environ, cleared), \
+                unittest.mock.patch.object(install.subprocess, "run", cmd):
+            install._enter_wsl()
+            self.assertEqual(os.environ["USERPROFILE"], str(self.root / "c" / "Users" / "me"))
+            self.assertEqual(os.environ["APPDATA"],
+                             str(self.root / "c" / "Users" / "me" / "AppData" / "Roaming"))
+            self.assertEqual(os.environ["ProgramFiles"], "")
+
+
 if __name__ == "__main__":
     unittest.main()

wiki/installer.md

@@ -291,6 +291,13 @@ not already found that way.
 Desktop installs are read from their own configuration, and several can be
 found on one machine.
 
+Under WSL both sides are searched. The Windows one is reached through its
+`/mnt/<drive>` mount: a `C:\` path from a rule or a config becomes
+`/mnt/c/...`, and the Windows variables the rules use (`USERPROFILE`,
+`APPDATA`, `LOCALAPPDATA`, `ProgramFiles`) are read through `cmd.exe` when
+WSL does not pass them. A forced `--platform retrobat` falls back to
+`/mnt/c/RetroBat/bios`.
+
 | Evidence | Platform | BIOS directory |
 |----------|----------|----------------|
 | `~/.config/EmuDeck/settings.sh` | EmuDeck | `emulationPath` + `/bios` |