tools/settings_migrate_group: refuse to overwrite an existing def file

Migrations now land from more than one workstation; a name chosen
locally can collide with a def file that arrived upstream in the
meantime, silently clobbering the other setting's single source.
The target def name must be fresh.

Author: libretroadmin

tools/settings_migrate_group.py

@@ -34,6 +34,8 @@
 def run(cmd): return subprocess.run(cmd, shell=True, capture_output=True, text=True)
 CSTR = r'"(?:[^"\\]|\\.)*"(?:\s*"(?:[^"\\]|\\.)*")*'
 TABLE, DEF, TITLE = sys.argv[1], sys.argv[2], sys.argv[3]
+assert not os.path.exists(os.path.join('settings', os.path.basename(DEF))), \
+    'def file %s already exists upstream - pick a different name' % DEF
 SIGS = [('S_BOOL','f, T, n, d, sd, df, c'),
         ('S_UINT','f, T, n, d, sd, df, c, mn, mx, st, ob, ok, rp'),
         ('S_INT', 'f, T, n, d, sd, df, c, mn, mx, st, ob, ok, rp'),