warn on ambiguous comments in config files

copyparty/__main__.py

@@ -1507,6 +1507,7 @@ def add_debug(ap):
     ap2.add_argument("--bf-nc", metavar="NUM", type=int, default=200, help="bak-flips: stop if there's more than \033[33mNUM\033[0m files at \033[33m--kf-dir\033[0m already; default: 6.3 GiB max (200*32M)")
     ap2.add_argument("--bf-dir", metavar="PATH", type=u, default="bf", help="bak-flips: store corrupted chunks at \033[33mPATH\033[0m; default: folder named 'bf' wherever copyparty was started")
     ap2.add_argument("--bf-log", metavar="PATH", type=u, default="", help="bak-flips: log corruption info to a textfile at \033[33mPATH\033[0m")
+    ap2.add_argument("--no-cfg-cmt-warn", action="store_true", help=argparse.SUPPRESS)
 
 
 # fmt: on

copyparty/authsrv.py

@@ -3017,6 +3017,19 @@ def expand_config_file(
 
     ret.append("#\033[36m closed{}\033[0m".format(ipath))
 
+    zsl = []
+    for ln in ret:
+        zs = ln.split("  #")[0]
+        if " #" in zs and zs.split("#")[0].strip():
+            zsl.append(ln)
+    if zsl and "no-cfg-cmt-warn" not in "\n".join(ret):
+        t = "\033[33mWARNING: there is less than two spaces before the # in the following config lines, so instead of assuming that this is a comment, the whole line will become part of the config value:\n\n>>> %s\n\nif you are familiar with this and would like to mute this warning, specify the global-option no-cfg-cmt-warn\n\033[0m"
+        t = t % ("\n>>> ".join(zsl),)
+        if log:
+            log(t)
+        else:
+            print(t, file=sys.stderr)
+
 
 def upgrade_cfg_fmt(
     log: Optional["NamedLogger"], args: argparse.Namespace, orig: list[str], cfg_fp: str