package.scm: (profile-derivation (%store) '())

package.scm: (profile-derivation (%store) '())

[Nikita Karetnikov]

[-- Attachment #1: Type: text/plain, Size: 697 bytes --]

I’d like to know how ‘roll-back’ creates an empty generation because
it’s necessary to do the same for ‘--delete-generations’.

However, I fail to understand how (profile-derivation (%store) ‘())
works (or any other function that uses (%store)).  I assume that some
code should set ‘%store’ to something else.  Like so:

scheme@(guix scripts package)> %store
$1 = #<<parameter> 934e7f8 proc: #<procedure 934e810 at ice-9/boot-9.scm:3154:17 () | (x)>>
scheme@(guix scripts package)> (%store)
$2 = #f
scheme@(guix scripts package)> (%store "FOO")
$3 = #f
scheme@(guix scripts package)> (%store)
$4 = "FOO"

But I don’t see anything similar in ‘package.scm’.

[-- Attachment #2: Type: application/pgp-signature, Size: 835 bytes --]

Re: package.scm: (profile-derivation (%store) '())

[Ludovic Courtès]

Nikita Karetnikov <nikita@karetnikov.org> skribis:

> I’d like to know how ‘roll-back’ creates an empty generation because
> it’s necessary to do the same for ‘--delete-generations’.
>
> However, I fail to understand how (profile-derivation (%store) ‘())
> works (or any other function that uses (%store)).  I assume that some
> code should set ‘%store’ to something else.  Like so:
>
> scheme@(guix scripts package)> %store
> $1 = #<<parameter> 934e7f8 proc: #<procedure 934e810 at ice-9/boot-9.scm:3154:17 () | (x)>>
> scheme@(guix scripts package)> (%store)
> $2 = #f
> scheme@(guix scripts package)> (%store "FOO")
> $3 = #f
> scheme@(guix scripts package)> (%store)
> $4 = "FOO"
>
> But I don’t see anything similar in ‘package.scm’.

‘%store’ is a SRFI-39 parameter (info "(guile) Parameters"), aka. a
dynamically-scoped variable.

It is initialized with the ‘parameterize’ form, which sets its value for
the dynamic extent of its body.

HTH,
Ludo’.

Re: package.scm: (profile-derivation (%store) '())

[Nikita Karetnikov]

[-- Attachment #1: Type: text/plain, Size: 1272 bytes --]

> ‘%store’ is a SRFI-39 parameter (info "(guile) Parameters"), aka. a
> dynamically-scoped variable.

> It is initialized with the ‘parameterize’ form, which sets its value for
> the dynamic extent of its body.

I don’t understand what code initializes ‘%store’.

For example, I have one generation in the ‘test’ profile.  So ‘test’
points to ‘test-1-link’.  If I do

scheme@(guix scripts package)> (roll-back "test")

I get an error

guix/derivations.scm:428:17: In procedure derivation->output-path:
guix/derivations.scm:428:17: In procedure struct_vtable: Wrong type argument in position 1 (expecting struct): #f

Entering a new prompt.  Type `,bt' for a backtrace or `,q' to continue.
scheme@(guix scripts package) [1]> 

This error is produced by (profile-derivation (%store) '()) since
‘%store’ is set to #f.

But why does this command work?

$ ./pre-inst-env guix package -p test --roll-back
switching from generation 1 to 0

As far as I understand, this code is called when the above command is
invoked:

    ;; First roll back if asked to.
    (if (and (assoc-ref opts 'roll-back?) (not dry-run?))
        (begin
          (roll-back profile)

I don’t see any references to ‘%store’ here.

[-- Attachment #2: Type: application/pgp-signature, Size: 835 bytes --]

Re: package.scm: (profile-derivation (%store) '())

[Ludovic Courtès]

Nikita Karetnikov <nikita@karetnikov.org> skribis:

>> ‘%store’ is a SRFI-39 parameter (info "(guile) Parameters"), aka. a
>> dynamically-scoped variable.
>
>> It is initialized with the ‘parameterize’ form, which sets its value for
>> the dynamic extent of its body.
>
> I don’t understand what code initializes ‘%store’.

This:

          (parameterize ((%store (open-connection)))
             ...)

> For example, I have one generation in the ‘test’ profile.  So ‘test’
> points to ‘test-1-link’.  If I do
>
> scheme@(guix scripts package)> (roll-back "test")
>
> I get an error
>
> guix/derivations.scm:428:17: In procedure derivation->output-path:
> guix/derivations.scm:428:17: In procedure struct_vtable: Wrong type argument in position 1 (expecting struct): #f
>
> Entering a new prompt.  Type `,bt' for a backtrace or `,q' to continue.
> scheme@(guix scripts package) [1]> 

I suspect it’s the ‘%guile-for-build’ parameter that’s set to #f instead
of being set to a derivation here.  There’s also a ‘parameterize’ form
for that one in guix/scripts/package.scm.

> But why does this command work?
>
> $ ./pre-inst-env guix package -p test --roll-back
> switching from generation 1 to 0

Because it’s designed to work!  :-)

> As far as I understand, this code is called when the above command is
> invoked:
>
>     ;; First roll back if asked to.
>     (if (and (assoc-ref opts 'roll-back?) (not dry-run?))
>         (begin
>           (roll-back profile)
>
> I don’t see any references to ‘%store’ here.

Look for ‘parameterize’; it’s dynamic scoping, which makes it less
visible.

HTH,
Ludo’.