* guix/build/store-copy.scm (store-info): Export.
* guix/store/database.scm (register-items): New procedure.
(register-path): Implement in terms of 'register-items'.
* gnu/build/install.scm (register-closure): Use 'register-items' instead
of 'for-each' and 'register-path'.
The previous implementation of 'read-reference-graph' was good enough
for many use cases, but it discarded the graph structure, which is
useful information in some cases.
* guix/build/store-copy.scm (<store-info>): New record type.
(read-reference-graph): Rewrite to return a list of <store-info>.
(closure-size, populate-store): Adjust accordingly.
* gnu/services/base.scm (references-file): Adjust accordingly.
* gnu/system/vm.scm (system-docker-image): Likewise.
* guix/scripts/pack.scm (squashfs-image, docker-image): Likewise.
* tests/gexp.scm ("gexp->derivation #:references-graphs"): Likewise.
* gnu/build/vm.scm (estimated-partition-size): New procedure.
* gnu/system/vm.scm (expression->derivation-in-linux-vm):
Change #:disk-image-size default to 'guess.
[builder]: When DISK-IMAGE-SIZE is 'guess, use
'estimated-partition-size' and compute and estimate of the image size.
(qemu-image): Likewise.
* guix/build/store-copy.scm (file-size, closure-size): New procedures.
* guix/scripts/system.scm (%default-options): Change 'image-size' to
'guess.
* doc/guix.texi (Building the Installation Image): Remove '--image-size'
flag from example.
(Invoking guix system): Document the image size estimate.
Ludovic Courtès