Previously the imported modules and extensions of EXP would be missing
from the load path of 'guix repl'.
* guix/inferior.scm (gexp->derivation-in-inferior)[script]: New
variable.
[trampoline]: Write (primitive-load #$script) to PIPE. Add #$output.
* tests/channels.scm ("channel-instances->manifest")[depends?]: Check
for requisites rather than direct references.
Adjust callers accordingly.
Previous 'channel-instance->manifest' would call
'latest-channel-derivation', which could trigger another round of
'latest-repository-commit' for no good reason.
* guix/channels.scm (resolve-dependencies): New procedure.
(channel-instance-derivations)[edges]: New variable.
[instance->derivation]: New procedure.
* tests/channels.scm (make-instance): Use 'checkout->channel-instance'
instead of 'channel-instance'.
("channel-instances->manifest"): New test.
* guix/channels.scm (<channel-metadata>): New record.
(read-channel-metadata, channel-instance-dependencies): New procedures.
(latest-channel-instances): Include channel dependencies; add optional
argument PREVIOUS-CHANNELS.
(channel-instance-derivations): Build derivation for additional channels and
add it as dependency to the channel instance derivation.
* doc/guix.texi (Channels): Add subsection "Declaring Channel Dependencies".
* tests/channels.scm: New file.
* Makefile.am (SCM_TESTS): Add it.
