channels: Interpret the 'commit' field of channel as a tag or commit.

Previously the 'commit' field would always be interpreted as a commit
ID.  This change adds flexibility, allowing for things like:

  guix time-machine --commit=v1.2.0 -- describe

* guix/channels.scm (channel-reference): Use 'tag-or-commit' rather than 'commit'.
* guix/inferior.scm (channel-full-commit): Likewise.
* doc/guix.texi (Invoking guix pull): Document it.
(Invoking guix time-machine): Likewise.
This commit is contained in:
Ludovic Courtès 2022-10-11 11:19:54 +02:00
parent 46f7011591
commit f36522416e
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3 changed files with 23 additions and 4 deletions

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@ -4645,7 +4645,7 @@ but it supports the following options:
@itemx --branch=@var{branch}
Download code for the @code{guix} channel from the specified @var{url}, at the
given @var{commit} (a valid Git commit ID represented as a hexadecimal
string), or @var{branch}.
string or the name of a tag), or @var{branch}.
@cindex @file{channels.scm}, configuration file
@cindex configuration file for channels
@ -4797,6 +4797,25 @@ of Guix to be used is defined by a commit or by a channel
description file created by @command{guix describe}
(@pxref{Invoking guix describe}).
Let's assume that you want to travel to those days of November 2020 when
version 1.2.0 of Guix was released and, once you're there, run the
@command{guile} of that time:
@example
guix time-machine --commit=v1.2.0 -- \
environment -C --ad-hoc guile -- guile
@end example
The command above fetches Guix@tie{}1.2.0 and runs its @command{guix
environment} command to spawn an environment in a container running
@command{guile} (@command{guix environment} has since been subsumed by
@command{guix shell}; @pxref{Invoking guix shell}). It's like driving a
DeLorean@footnote{If you don't know what a DeLorean is, consider
traveling back to the 1980's.}! The first @command{guix time-machine}
invocation can be expensive: it may have to download or even build a
large number of packages; the result is cached though and subsequent
commands targeting the same commit are almost instantaneous.
The general syntax is:
@example
@ -4813,7 +4832,7 @@ this revision are the same as for @command{guix pull} (@pxref{Invoking guix pull
@itemx --branch=@var{branch}
Use the @code{guix} channel from the specified @var{url}, at the
given @var{commit} (a valid Git commit ID represented as a hexadecimal
string), or @var{branch}.
string or the name of a tag), or @var{branch}.
@item --channels=@var{file}
@itemx -C @var{file}

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@ -248,7 +248,7 @@ (define (channel-reference channel)
'latest-repository-commit'."
(match (channel-commit channel)
(#f `(branch . ,(channel-branch channel)))
(commit `(commit . ,(channel-commit channel)))))
(commit `(tag-or-commit . ,(channel-commit channel)))))
(define sexp->channel-introduction
(match-lambda

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@ -835,7 +835,7 @@ (define (channel-full-commit channel)
(branch (channel-branch channel)))
(if (and commit (commit-id? commit))
commit
(let* ((ref (if commit `(commit . ,commit) `(branch . ,branch)))
(let* ((ref (if commit `(tag-or-commit . ,commit) `(branch . ,branch)))
(cache commit relation
(update-cached-checkout (channel-url channel)
#:ref ref