bug#66260: 29.0.92; project.el should support copying a file path relative to the project root

[sbaugh]

Dmitry Gutov <dmitry@gutov.dev> writes:
> On 02/10/2023 09:53, Juri Linkov wrote:
>>>> 'C-x p w' does make sense as such, but it would be unfortunate if we
>>>> find a more important command later which fits the 'w' mnemonics. Maybe
>>>> 'C-x p W' would be a more conservative choice.
>>> Or even "C-x p C-w".
>> Or 'C-x p C-c' like 'c' in Info-mode-map for Info-copy-current-node-name.
>
> That one was probably made from the CUA user's standpoint.
>
> I sympathize, but even Info-mode-map has a 'w' binding (thanks to you,
> looks like).
>
> So C-w or M-w seem like a better choice for the default bindings.

I don't think C-x p w is quite necessary.  But even if it was, I think
there's a good other candidate for what it should do: copy the project
root.  That would also be pretty useful.

For example, I often move a patch between two projects by first
rendering it in one project (with C-x v D), entering M-x cd
other/project/root in the *vc-diff* buffer, and then applying the diff.
If there was a quick way to get other/project/root, it would speed this
up.

Sometimes I also run shell commands which need the project root.

I can always do C-x p D then copy the file name of that buffer, but
that's about as painful as C-x C-j C-u C-u w, so if C-x C-j C-u C-u w is
too cumbersome then it seems to me that so is C-x p D and copy.