Incorrect interpretation of double dash

This issue is about -- (perhaps also called: double minus, minus minus, double dash, double hyphen, or something like that, I don't actually know).

At first glance, -- is just a separator between options and arguments – and usually that is correct!

However, it seems that if supplied as argument to an option, then GNU and clap differ:

• GNU says it is NOT a separator, and instead a regular argument.
• clap says it IS a separator, and complains about the missing argument.

$ find -maxdepth 1 -name 'README*' -print0 > ./--
$ hd ./--
00000000  2e 2f 52 45 41 44 4d 45  2e 70 61 63 6b 61 67 65  |./README.package|
00000010  2e 6d 64 00 2e 2f 52 45  41 44 4d 45 2e 6d 64 00  |.md../README.md.|
00000020
$ ~/workspace/gnu/src/du --files0-from --
4	./README.package.md
8	./README.md
$ cargo +stable --quiet run du --files0-from --
error: a value is required for '--files0-from <FILE>' but none was supplied

For more information, try '--help'.
[$? = 1]

This probably affects nearly all utils (and not just du). Since this is unfixable in clap, this is yet another point in favor of https://github.com/uutils/coreutils/issues/4254.

No repository file or test is named. Start by reproducing the provided GNU du and cargo +stable --quiet run du --files0-from -- commands, then inspect how clap parses --files0-from and compare the scope with uutils/coreutils issue #4254. Done means establishing whether this repository can address the discrepancy or documenting why it belongs elsewhere.