make volflags less confusing

1. warn about unrecognized volflags

previously, when specifying an unknown volflag, it would
be silently ignored, giving the impression that it applied

2. also allow uppercase, kebab-case
    (previously, only snake_case was accepted)

3. mention every volflag in --help-flags
    (some volflags were missing)

copyparty/authsrv.py

@@ -1289,10 +1289,10 @@ class AuthSrv(object):
                 # one or more bools before the final flag; eat them
                 n1, uname = uname.split(",", 1)
                 for _, vp, _, _ in vols:
-                    self._read_volflag(flags[vp], n1, True, False)
+                    self._read_volflag(vp, flags[vp], n1, True, False)
 
             for _, vp, _, _ in vols:
-                self._read_volflag(flags[vp], uname, cval, False)
+                self._read_volflag(vp, flags[vp], uname, cval, False)
 
             return
 
@@ -1379,13 +1379,27 @@ class AuthSrv(object):
 
     def _read_volflag(
         self,
+        vpath: str,
         flags: dict[str, Any],
         name: str,
         value: Union[str, bool, list[str]],
         is_list: bool,
     ) -> None:
+        if name not in flagdescs:
+            name = name.lower()
+
+            # volflags are snake_case, but a leading dash is the removal operator
+            if name not in flagdescs and "-" in name[1:]:
+                name = name[:1] + name[1:].replace("-", "_")
+
         desc = flagdescs.get(name.lstrip("-"), "?").replace("\n", " ")
 
+        if not name:
+            self._e("└─unreadable-line")
+            t = "WARNING: the config for volume [/%s] indicated that a volflag was to be defined, but the volflag name was blank"
+            self.log(t % (vpath,), 3)
+            return
+
         if re.match("^-[^-]+$", name):
             t = "└─unset volflag [{}]  ({})"
             self._e(t.format(name[1:], desc))
@@ -1557,6 +1571,17 @@ class AuthSrv(object):
             vol.all_vps.sort(key=lambda x: len(x[0]), reverse=True)
             vol.root = vfs
 
+        zs = "neversymlink"
+        k_ign = set(zs.split())
+        for vol in vfs.all_vols.values():
+            unknown_flags = set()
+            for k, v in vol.flags.items():
+                if k not in flagdescs and k not in k_ign:
+                    unknown_flags.add(k)
+            if unknown_flags:
+                t = "WARNING: the config for volume [/%s] has unrecognized volflags; will ignore: '%s'"
+                self.log(t % (vol.vpath, "', '".join(unknown_flags)), 3)
+
         enshare = self.args.shr
         shr = enshare[1:-1]
         shrs = enshare[1:]
@@ -1975,7 +2000,9 @@ class AuthSrv(object):
             # append additive args from argv to volflags
             hooks = "xbu xau xiu xbc xac xbr xar xbd xad xm xban".split()
             for name in "mtp on404 on403".split() + hooks:
-                self._read_volflag(vol.flags, name, getattr(self.args, name), True)
+                self._read_volflag(
+                    vol.vpath, vol.flags, name, getattr(self.args, name), True
+                )
 
             for hn in hooks:
                 cmds = vol.flags.get(hn)