Ludovic Courtès (2014-10-05 00:23 +0400) wrote:
> Alex Kost <alez...@gmail.com> skribis:>
[...]
>> - (Not related to this patch, but still …) Currently with “roll-back”,
>> we can only switch to the previous generation. What about adding a
>> possibility to switch to any generation? So that we could use
>> something like this:
>>
>> guix package --switch-generation=7
>>
>> Also such functionality can be added to Emacs UI: for example pressing
>> "C" on a generation in *Guix Generation List* will make this
>> generation the current one.
>>
>> So ‘roll-back’ procedure may become a special case of the
>> ‘switch-generation’ one. WDYT?
>
> I think it’s a good idea! (I think it was suggested in earlier
> discussions, but never implemented.)
Andreas Enge (2014-10-05 18:44 +0400) wrote:
[...]
> Actually, sometimes I would like to switch to the next generation ("-roll-
> forward", in a sense): I install something, go back with "--roll-back",
> and might like to go just one forward again.
>
> So how about the following:
> --switch-generation=1
> goes to generation 1;
> --switch-generation=-1
> goes 1 generation back;
> --switch-generation=+1
> goes one generation forward.
Thanks for the great idea!
————————————————————————————————————————————————————————————————
A patch is attached. Some comments:
- ‘shitted-generation’ is not a very good name, I think. Ideas?
- ‘previous-generation-number’ may use ‘shifted-generation’ now:
(define* (previous-generation-number profile #:optional
(number (generation-number profile)))
"Return the number of the generation before generation NUMBER of
PROFILE, or 0 if none exists. It could be NUMBER - 1, but it's not the
case when generations have been deleted (there are \"holes\")."
(or (shifted-generation profile -1 number)
0))
Worth changing?
- Perhaps it would be better to make 2 commits (?): one for adding
‘shifted-generation’ and ‘switch-to-generation’ procedures to (guix
profiles) and another is for adding the “--switch-generation” option
itself.
- Also I made a couple of cosmetic changes in “guix/scripts/package.scm”:
* ‘filter-map’ was replaced by 'for-each' because it was called only for
side effects there;
* ‘begin’ was removed from ‘cond’.
I think these changes do not deserve a separate commit and may stay in
this patch. Is it OK?
>From 3cc52d1aade5e9723c38c0af5fa4437cbdf1a9b6 Mon Sep 17 00:00:00 2001
From: Alex Kost <alez...@gmail.com>
Date: Mon, 6 Oct 2014 17:35:51 +0400
Subject: [PATCH] guix package: Add '--switch-generation' option.
* doc/guix.texi (Invoking guix package): Update documentation.
* guix/profiles.scm (shifted-generation, switch-to-generation): New
procedures.
* guix/scripts/package.scm: Add '--switch-generation' option.
(switch-to-previous-generation): Use 'switch-to-generation'.
---
doc/guix.texi | 15 +++++++++++++++
guix/profiles.scm | 36 +++++++++++++++++++++++++++++++++++-
guix/scripts/package.scm | 44 +++++++++++++++++++++++++++++++++-----------
3 files changed, 83 insertions(+), 12 deletions(-)
diff --git a/doc/guix.texi b/doc/guix.texi
index f6357bd..c6921b1 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -784,6 +784,21 @@ Installing, removing, or upgrading packages from a generation that has
been rolled back to overwrites previous future generations. Thus, the
history of a profile's generations is always linear.
+@item --switch-generation=@var{pattern}
+@itemx -S @var{pattern}
+Switch to a particular generation defined by @var{pattern}.
+
+@var{pattern} may be either a generation number or a number prefixed
+with ``+'' or ``-''. The latter means: move forward/backward by a
+specified number of generations. For example, if you want to return to
+the latest generation after @code{--roll-back}, use
+@code{--switch-generation=+1}.
+
+The difference between @code{--roll-back} and
+@code{--switch-generation=-1} is that @code{--switch-generation} will
+not make a zeroth generation, so if a specified generation does not
+exist, the current generation will not be changed.
+
@item --search-paths
@cindex search paths
Report environment variable definitions, in Bash syntax, that may be
diff --git a/guix/profiles.scm b/guix/profiles.scm
index 18733a6..589402e 100644
--- a/guix/profiles.scm
+++ b/guix/profiles.scm
@@ -71,9 +71,11 @@
generation-number
generation-numbers
profile-generations
+ shifted-generation
previous-generation-number
generation-time
- generation-file-name))
+ generation-file-name
+ switch-to-generation))
;;; Commentary:
;;;
@@ -569,6 +571,21 @@ former profiles were found."
'()
generations)))
+(define* (shifted-generation profile shift
+ #:optional (current (generation-number profile)))
+ "Return PROFILE's generation shifted from the CURRENT generation by SHIFT.
+SHIFT is a positive or negative number.
+Return #f if there is no such generation."
+ (let* ((abs-shift (abs shift))
+ (numbers (profile-generations profile))
+ (from-current (memq current
+ (if (negative? shift)
+ (reverse numbers)
+ numbers))))
+ (and from-current
+ (< abs-shift (length from-current))
+ (list-ref from-current abs-shift))))
+
(define (previous-generation-number profile number)
"Return the number of the generation before generation NUMBER of
PROFILE, or 0 if none exists. It could be NUMBER - 1, but it's not the
@@ -589,4 +606,21 @@ case when generations have been deleted (there are \"holes\")."
(make-time time-utc 0
(stat:ctime (stat (generation-file-name profile number)))))
+(define (switch-to-generation profile number)
+ "Atomically switch PROFILE to the generation NUMBER."
+ (let ((current (generation-number profile))
+ (file (generation-file-name profile number)))
+ (cond ((not (file-exists? profile))
+ (format (current-error-port)
+ (_ "profile '~a' does not exist~%")
+ profile))
+ ((not (file-exists? file))
+ (format (current-error-port)
+ (_ "generation ~a does not exist~%")
+ number))
+ (else
+ (format #t (_ "switching from generation ~a to ~a~%")
+ current number)
+ (switch-symlinks profile file)))))
+
;;; profiles.scm ends here
diff --git a/guix/scripts/package.scm b/guix/scripts/package.scm
index fc9c37b..b071029 100644
--- a/guix/scripts/package.scm
+++ b/guix/scripts/package.scm
@@ -96,12 +96,9 @@ return PROFILE unchanged. The goal is to treat '-p ~/.guix-profile' as if
(define (switch-to-previous-generation profile)
"Atomically switch PROFILE to the previous generation."
- (let* ((number (generation-number profile))
- (previous-number (previous-generation-number profile number))
- (previous-generation (generation-file-name profile previous-number)))
- (format #t (_ "switching from generation ~a to ~a~%")
- number previous-number)
- (switch-symlinks profile previous-generation)))
+ (let* ((current (generation-number profile))
+ (previous (previous-generation-number profile current)))
+ (switch-to-generation profile previous)))
(define (roll-back store profile)
"Roll back to the previous generation of PROFILE."
@@ -409,6 +406,9 @@ Install, remove, or upgrade PACKAGES in a single transaction.\n"))
-d, --delete-generations[=PATTERN]
delete generations matching PATTERN"))
(display (_ "
+ -S, --switch-generation=PATTERN
+ switch to a generation matching PATTERN"))
+ (display (_ "
-p, --profile=PROFILE use PROFILE instead of the user's default profile"))
(newline)
(display (_ "
@@ -488,6 +488,10 @@ Install, remove, or upgrade PACKAGES in a single transaction.\n"))
(values (alist-cons 'delete-generations (or arg "")
result)
#f)))
+ (option '(#\S "switch-generation") #t #f
+ (lambda (opt name arg result arg-handler)
+ (values (alist-cons 'switch-generation arg result)
+ #f)))
(option '("search-paths") #f #f
(lambda (opt name arg result arg-handler)
(values (cons `(query search-paths) result)
@@ -713,13 +717,31 @@ more information.~%"))
(generation-number profile))
;; First roll back if asked to.
- (cond ((and (assoc-ref opts 'roll-back?) (not dry-run?))
- (begin
- (roll-back (%store) profile)
- (process-actions (alist-delete 'roll-back? opts))))
+ (cond ((and (assoc-ref opts 'roll-back?)
+ (not dry-run?))
+ (roll-back (%store) profile)
+ (process-actions (alist-delete 'roll-back? opts)))
+ ((and (assoc-ref opts 'switch-generation)
+ (not dry-run?))
+ (for-each
+ (match-lambda
+ (('switch-generation . pattern)
+ (let* ((number (string->number pattern))
+ (number (and number
+ (case (string-ref pattern 0)
+ ((#\+ #\-)
+ (shifted-generation profile number))
+ (else number)))))
+ (if number
+ (switch-to-generation profile number)
+ (format (current-error-port)
+ "Cannot switch to generation '~a'~%" pattern)))
+ (process-actions (alist-delete 'switch-generation opts)))
+ (_ #f))
+ opts))
((and (assoc-ref opts 'delete-generations)
(not dry-run?))
- (filter-map
+ (for-each
(match-lambda
(('delete-generations . pattern)
(cond ((not (file-exists? profile)) ; XXX: race condition
--
2.1.2
--
Thanks,
Alex
