bug#49776: 28.0.50; Incorrect username completion results reported by `read-file-name-interal`

[Daniel Mendler <mail@daniel-mendler.de>]

On 7/30/21 2:50 PM, Lars Ingebrigtsen wrote:
> But you said it returned "/.config/~man" for you (while it returns
> "/.config/~man/" for me) (note trailing slash)...

Yes, this was a typo from my side, sorry for that. Please look at the
other examples I've sent.

So to describe this better: (all-completions "~/etc/~man"
'read-file-name-internal) returns ("/etc/~man/"). In contrast
(all-completions "/usr/~man" 'read-file-name-internal) returns ("man/").
"/etc/~man/ is neither a valid user name nor a valid file path. I have
the user "man" on my system of course (I am also on a recent Debian).

So the problem here is that in to even call the completion table with
"~/etc/~man", the completion boundary is placed such that the string
behind the first "~" is completed. If I read Eli correctly, he says that
this is the expected behavior, while I would have expected that the
completion boundary is placed behind the second "~", such that the
completion table does not return odd looking results like "/etc/~man".
Furthermore the string before the first "~" can be considered shadowed.
So maybe the problem here is not with the results returned by
`all-completions` but rather with the completion boundaries. I think
this needs further investigation from my side.

Daniel