extmod/vfs_rom: Implement minimal VfsRom.getcwd() method.

dpgeorge · dpgeorge · commit e4051a1ca667 · 2025-03-27T17:04:12.000+11:00
This is needed if you chdir to a ROMFS and want to query your current
directory.

Prior to this change, using `os.getcwd()` when in a ROMFS would raise:

    AttributeError: 'VfsRom' object has no attribute 'getcwd'

Signed-off-by: Damien George &lt;damien@micropython.org&gt;
diff --git a/extmod/vfs_rom.c b/extmod/vfs_rom.c
@@ -300,6 +300,13 @@ static mp_obj_t vfs_rom_chdir(mp_obj_t self_in, mp_obj_t path_in) {
 }
 static MP_DEFINE_CONST_FUN_OBJ_2(vfs_rom_chdir_obj, vfs_rom_chdir);
 
+static mp_obj_t vfs_rom_getcwd(mp_obj_t self_in) {
+    (void)self_in;
+    // The current directory is always the root of the ROMFS.
+    return MP_OBJ_NEW_QSTR(MP_QSTR_);
+}
+static MP_DEFINE_CONST_FUN_OBJ_1(vfs_rom_getcwd_obj, vfs_rom_getcwd);
+
 typedef struct _vfs_rom_ilistdir_it_t {
     mp_obj_base_t base;
     mp_fun_1_t iternext;
@@ -436,6 +443,7 @@ static const mp_rom_map_elem_t vfs_rom_locals_dict_table[] = {
     { MP_ROM_QSTR(MP_QSTR_open), MP_ROM_PTR(&vfs_rom_open_obj) },
 
     { MP_ROM_QSTR(MP_QSTR_chdir), MP_ROM_PTR(&vfs_rom_chdir_obj) },
+    { MP_ROM_QSTR(MP_QSTR_getcwd), MP_ROM_PTR(&vfs_rom_getcwd_obj) },
     { MP_ROM_QSTR(MP_QSTR_ilistdir), MP_ROM_PTR(&vfs_rom_ilistdir_obj) },
     { MP_ROM_QSTR(MP_QSTR_stat), MP_ROM_PTR(&vfs_rom_stat_obj) },
     { MP_ROM_QSTR(MP_QSTR_statvfs), MP_ROM_PTR(&vfs_rom_statvfs_obj) },
diff --git a/tests/extmod/vfs_rom.py b/tests/extmod/vfs_rom.py
@@ -408,9 +408,11 @@ def test_listdir(self):
 
     def test_chdir(self):
         os.chdir("/test_rom")
+        self.assertEqual(os.getcwd(), "/test_rom")
         self.assertEqual(os.listdir(), self.romfs_listdir)
 
         os.chdir("/test_rom/")
+        self.assertEqual(os.getcwd(), "/test_rom")
         self.assertEqual(os.listdir(), self.romfs_listdir)
 
         # chdir within the romfs is not implemented.
