Fixes a bug whereby 'cached-channel-instance' would potentially consider
cache entries obsolete too early because they refer to items in the
store, which is mounted as 'noatime' on Guix System.
* guix/cache.scm (file-expiration-time): Use 'lstat' and
'false-if-exception' rather than 'stat'. This matches what (guix
scripts shell) does.
This ensures ~/.cache/guix/checkouts is periodically cleaned up.
* guix/git.scm (cached-checkout-expiration)
(%checkout-cache-cleanup-period): New variables.
(delete-checkout): New procedure.
(update-cached-checkout)[cache-entries]: New procedure.
Add call to 'maybe-remove-expired-cache-entries'.
* guix/cache.scm (file-expiration-time): Add optional 'timestamp'
parameter and honor it.
* guix/cache.scm, tests/cache.scm: New files.
* Makefile.am (MODULES, SCM_TESTS): Add them.
* guix/scripts/substitute.scm (obsolete?): Remove.
(remove-expired-cached-narinfos): Rename to...
(cached-narinfo-expiration-time): ... this. Remove the removal part and
only keep the expiration time part.
(narinfo-cache-directories): Add optional 'directory' parameter and
honor it.
(maybe-remove-expired-cached-narinfo): Remove.
(cached-narinfo-files): New procedure.
(guix-substitute): Use 'maybe-remove-expired-cache-entries' instead of
'maybe-remove-expired-cached-narinfo'.
Ludovic Courtès
zimoun