There's a closed pull request on the void-packages repository

[RFC] xbps-src: add a command `show-diff`
https://github.com/void-linux/void-packages/pull/53950

Description:
Usage: ./xbps-src show-diff PKG

Shows differences between the original sources and $wrksrc, in the form
of a patch that can be used for the template.

Note this ignores new files.


#### Testing the changes
- I tested the changes in this PR: **briefly**


#### Alternatives

One alternative suggested in irc is to use unpatch from

https://leahneukirchen.org/dotfiles/bin/unpatch

Save the original files as .orig, then run

- `unpatch -g -p3 masterdir-*/builddir/pkg-ver`

With vim, one can use `:set patchmode=.orig`


Two more suggestions from irc related to this:

 - `alias xpatch="nvim -c 'set patchmode=.orig'"`

 - `autocmd BufNewFile,BufRead masterdir-*/builddir/* setlocal patchmode=.orig`