Re: A plan for parameterized packages

[zimoun]

Hi Lduo,

On Sun, 15 Nov 2020 at 17:33, Ludovic Courtès <ludo@gnu.org> wrote:

> That said, this message is about a possible implementation of package
> parameters, so here we go.  :-)

Cool!


> To me the requirements for package parameters are:
>
>   1. it must be possible to discover them and choose them from the UI;
>
>   2. they must contain on-line internationalized documentation such that
>      the UI can list a package’s parameters and their type;

Except ’boolean’, which kind of type do you have in mind?  Aside that
you did not find examples of packages requiring parameters. ;-)

The answer leads to your point #4.


>   3. the chosen parameters when installing a package in a profile must
>      be preserved;

You mean track the parameters with ’properties’ in <profile>/manifest,
right?


>   4. it must be possible to enumerate all the possible values of a
>      parameter, and thus to build the Cartesian product of all the
>      possible parameter combinations of a package (or of a package
>      graph!), so we can test those combinations as much as possible.

The values of the option are therefore known at package time, right?
However, this implies restricted possibility for the type, right?


> Subject: [PATCH 1/4] DRAFT Add (guix parameters).
>
> DRAFT: Missing tests & doc.
>
> * guix/parameters.scm: New file.
> * Makefile.am (MODULES): Add it.
> ---

[...]

> diff --git a/guix/parameters.scm b/guix/parameters.scm
> +
> +;; Type of a package parameter.
> +(define-record-type* <parameter-type> parameter-type
> +  make-parameter-type
> +  parameter-type?
> +  (name          parameter-type-name)              ;debugging purposes only!
> +  (string->value parameter-type-string->value)
> +  (value->string parameter-type-value->string)
> +  (universe      parameter-type-universe))
> +
> +(define boolean
> +  ;; The Boolean parameter type.
> +  (parameter-type (name 'boolean)
> +                  (universe '(#true #false))
> +                  (value->string
> +                   (match-lambda
> +                     (#f "false")
> +                     (#t "true")))
> +                  (string->value
> +                   (lambda (str)
> +                     (cond ((string-ci=? str "true")
> +                            #t)
> +                           ((string-ci=? str "false")
> +                            #f)
> +                           (else
> +                            (raise (condition
> +                                    (&message (message "wrong 
> value"))))))))))

The types will be “hard-coded“ here, right?  Boolean being the simplest
example and imagination just needs to be released, right? :-)



> Subject: [PATCH 2/4] DRAFT transformations: Add '--with-parameter'.
>
> DRAFT: Missing tests & doc.
>
> * guix/transformations.scm (evaluate-parameter-specs)
> (transform-package-parameters): New procedures.
> (%transformations, %transformation-options): Add 'with-parameter'.
> ---
>  guix/transformations.scm | 39 +++++++++++++++++++++++++++++++++++++++
>  1 file changed, 39 insertions(+)
>
> diff --git a/guix/transformations.scm b/guix/transformations.scm

[...]

> +(define (evaluate-parameter-specs specs proc)
> +  "Parse SPECS, a list of strings like \"bitlbee=purple=true\", and return a
> +list of spec/procedure pairs, where (PROC PACKAGE PARAMETER VALUE) is called
> +to return the replacement package.  Raise an error if an element of SPECS 
> uses
> +invalid syntax, or if a package it refers to could not be found."
> +  (map (lambda (spec)
> +         (match (string-tokenize spec %not-equal)
> +           ((spec name value)
> +            (define (replace old)
> +              (proc old name value))
> +
> +            (cons spec replace))
> +           (_
> +            (raise
> +             (formatted-message
> +              (G_ "invalid package parameter specification: ~s")
> +              spec)))))
> +       specs))

Here ’proc’ could be anything, right?  But then…

> +(define (transform-package-parameters replacement-specs)
> +  "Return a procedure that, when passed a package, replaces its direct
> +dependencies according to REPLACEMENT-SPECS.  REPLACEMENT-SPECS is a list of
> +strings like \"guile-next=stable-3.0\" meaning that packages are built using
> +'guile-next' from the latest commit on its 'stable-3.0' branch."
> +  (define (replace old name value)
> +    (set-package-parameter-value old name value))
> +
> +  (let* ((replacements (evaluate-parameter-specs replacement-specs
> +                                                 replace))
> +         (rewrite      (package-input-rewriting/spec replacements)))
> +    (lambda (obj)
> +      (if (package? obj)
> +          (rewrite obj)
> +          obj))))

… it is ’set-package-parameter-value’.  It is not clear in my mind.
Does this constrain the hypothetical types?


Cheers,
simon