Hi,

> [...]
> 
> where ’make-linux-libre-source’ returns a ’computed-origin-method’.  And
> the ’origin-uri’ of ’linux-libre-5.14-pristine-source’ is a ’gexp’.
> Then inside this ’gexp’, you can read the ’%upstream-linux-source’ URL:
> 
> --8<---------------cut here---------------start------------->8---
> #<gexp-input native
>  #<origin
>   #"mirror://kernel.org/linux/kernel/v5.x/linux-5.13.14.tar.xz"
>   #<content-hash sha256:06lbjsbr86qa8yai5gfclbfxvcqsw33kxj9b4r93hh6z1wajmx82>
> --8<---------------cut here---------------end--------------->8---
> 
> and I do not know if it is possible to extract such thing.

To extract the <origin> from the <gexp-input>, use gexp-input-thing.
To extract the <gexp-input> from the <gexp>, use the unexported
gexp-references.

Greetings,
Maxime