[bug#63985,v3,06/11] services: configuration: New generic-ini module.

Implements a ‘serialize-ini-configuration’ procedure for serializing
record-types defined with define-configuration into generic INI files.

* gnu/services/configuration/generic-ini.scm: New module.
* tests/services/configuration/generic-ini.scm: Add tests for new module.
* Makefile.am: Register tests.
* gnu/local.mk: Register module.
---
 Makefile.am                                  |   1 +
 gnu/local.mk                                 |   1 +
 gnu/services/configuration/generic-ini.scm   | 165 +++++++++++++++++++
 tests/services/configuration/generic-ini.scm | 129 +++++++++++++++
 4 files changed, 296 insertions(+)
 create mode 100644 gnu/services/configuration/generic-ini.scm
 create mode 100644 tests/services/configuration/generic-ini.scm

Hi,

Bruno Victal <mirai@makinata.eu> writes:

> Implements a ‘serialize-ini-configuration’ procedure for serializing
> record-types defined with define-configuration into generic INI files.
>
> * gnu/services/configuration/generic-ini.scm: New module.
> * tests/services/configuration/generic-ini.scm: Add tests for new module.
> * Makefile.am: Register tests.
> * gnu/local.mk: Register module.

Nitpick: I'd perhaps rename the module simply 'ini', to shorten a bit
the module namespace, already quite long.

> ---
>  Makefile.am                                  |   1 +
>  gnu/local.mk                                 |   1 +
>  gnu/services/configuration/generic-ini.scm   | 165 +++++++++++++++++++
>  tests/services/configuration/generic-ini.scm | 129 +++++++++++++++
>  4 files changed, 296 insertions(+)
>  create mode 100644 gnu/services/configuration/generic-ini.scm
>  create mode 100644 tests/services/configuration/generic-ini.scm
>
> diff --git a/Makefile.am b/Makefile.am
> index a386e6033c..b6d048f140 100644
> --- a/Makefile.am
> +++ b/Makefile.am
> @@ -553,6 +553,7 @@ SCM_TESTS =					\
>    tests/services.scm				\
>    tests/services/file-sharing.scm		\
>    tests/services/configuration.scm		\
> +  tests/services/configuration/generic-ini.scm	\
>    tests/services/lightdm.scm			\
>    tests/services/linux.scm			\
>    tests/services/telephony.scm			\
> diff --git a/gnu/local.mk b/gnu/local.mk
> index e65888a044..796ac33107 100644
> --- a/gnu/local.mk
> +++ b/gnu/local.mk
> @@ -670,6 +670,7 @@ GNU_SYSTEM_MODULES =				\
>    %D%/services/cgit.scm			\
>    %D%/services/ci.scm				\
>    %D%/services/configuration.scm		\
> +  %D%/services/configuration/generic-ini.scm	\
>    %D%/services/cuirass.scm			\
>    %D%/services/cups.scm				\
>    %D%/services/databases.scm			\
> diff --git a/gnu/services/configuration/generic-ini.scm b/gnu/services/configuration/generic-ini.scm
> new file mode 100644
> index 0000000000..4f83cce13a
> --- /dev/null
> +++ b/gnu/services/configuration/generic-ini.scm
> @@ -0,0 +1,165 @@
> +;;; GNU Guix --- Functional package management for GNU
> +;;; Copyright © 2023 Bruno Victal <mirai@makinata.eu>
> +;;;
> +;;; This file is part of GNU Guix.
> +;;;
> +;;; GNU Guix is free software; you can redistribute it and/or modify it
> +;;; under the terms of the GNU General Public License as published by
> +;;; the Free Software Foundation; either version 3 of the License, or (at
> +;;; your option) any later version.
> +;;;
> +;;; GNU Guix is distributed in the hope that it will be useful, but
> +;;; WITHOUT ANY WARRANTY; without even the implied warranty of
> +;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +;;; GNU General Public License for more details.
> +;;;
> +;;; You should have received a copy of the GNU General Public License
> +;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
> +
> +(define-module (gnu services configuration generic-ini)
> +  #:use-module (gnu services configuration)
> +  #:use-module (guix gexp)
> +  #:use-module (srfi srfi-9)
> +  #:use-module (srfi srfi-171)
> +  #:use-module (srfi srfi-171 meta)
> +  #:use-module (ice-9 match)
> +  #:export (ini-entry?
> +            list-of-ini-entries?
> +
> +            ini-entries
> +            ini-entries?
> +            entries
> +
> +            serialize-ini-configuration
> +            generic-ini-serialize-string
> +            generic-ini-serialize-boolean
> +            generic-ini-serialize-ini-entry
> +            generic-ini-serialize-list-of-ini-entries))
> +
> +;;;
> +;;; Generic INI serializer
> +;;;
> +

Nothing here?  I'd turn this into a Commentary comment, and document
that this is intended to match in behavior SRFI-233, so that it can
eventually be replaced without much fuss when it lands to Guile.

> +
> +;;;
> +;;; Predicates
> +;;;
> +
> +;; This is the same format used in SRFI-233 but without comment support.
> +(define ini-entry?
> +  (match-lambda
> +    (((? symbol?) (? symbol?) (? string?)) #t)
> +    (_ #f)))
> +
> +(define list-of-ini-entries?
> +  (list-of ini-entry?))
> +
> +;;
> +;; Overall design document
> +;;
> +;; This module implements a generic INI serializer for a record-type defined
> +;; using define-configuration.
> +;; It expects that the serialize-<type> procedures return a list with
> +;; three elements of the form:
> +;;    (list section key value)
> +;; Where ‘section’ and ‘key’ are symbols and ‘value’ is a string.
> +;; For serializing procedures that have to return multiple entries at once,
> +;; such as encountered when synthesizing configuration from a record object
> +;; or “escape hatch fields”, it must wrap the result by calling ‘ini-entries’
> +;; with a list of INI-entries as described above.
> +;; This is implemented as a constructor for a SRFI-9 record type named
> +;; “<ini-entries>”.
> +;;
> +;; The fields within define-configuration do not have to be ordered in,
> +;; any way whatsoever as the ‘serialize-ini’ will group them up automatically.
> +;; This implies that no assumptions should be made regarding the order of the
> +;; values in the serializied INI output.
> +;;
> +;; Additional notes:
> +;; Q: Why not replace rcons with string-append and forego the ungexp-splice?
> +;; A: The transduction happens outside of the G-Exp while the final string-append
> +;;    takes place in the G-Exp.
> +;;
> +;; Debugging tips: Open a REPL and try one transducer at a time from
> +;; ‘ini-transducer’.
> +;;

This should go to the Commentary section.

> +
> +;; A “bag” holding multiple ini-entries.
> +(define-record-type <ini-entries>
> +  (ini-entries val)
> +  ini-entries?
> +  (val entries))
> +
> +(define (add-section-header partition)
> +  (let ((header (caar partition)))
> +    (cons (list header)
> +          partition)))
> +
> +(define serializer
> +  (match-lambda
> +    ((section)
> +     #~(format #f "[~a]~%" '#$section))
> +    ((section key value)
> +     #~(format #f "~a=~a~%" '#$key #$value))
> +    ;; Used for the newline between sections.
> +    ('*section-separator* "\n")))
> +
> +(define ini-transducer
> +  (compose (tpartition car)
> +           (tmap add-section-header)
> +           (tadd-between '(*section-separator*))
> +           tconcatenate
> +           (tmap serializer)))
> +
> +;; A selective version of ‘tconcatenate’ but for ‘<ini-entries>’ objects only.
> +(define (tconcatenate-ini-entries reducer)
> +  (case-lambda
> +    (() '())
> +    ((result) (reducer result))
> +    ((result input)
> +     (if (ini-entries? input)
> +         (list-reduce (preserving-reduced reducer) result (entries input))
> +         (reducer result input)))))
> +
> +;; A “first-pass” serialization is performed and sorted in order
> +;; to group up the fields by “section” before passing through the
> +;; transducer.
> +(define (serialize-ini-configuration config fields)
> +  (let* ((srfi-233-IR
> +          ;; First pass: “serialize” into a (disordered) list of
> +          ;; SRFI-233 entries.
> +          (list-transduce (compose (base-transducer config)
> +                                   tconcatenate-ini-entries)
> +                          rcons fields))
> +         (comparator (lambda (x y)
> +                       ;; Sort the SRFI-233 entries by section.
> +                       (string<=? (symbol->string (car x))
> +                                  (symbol->string (car y)))))
> +         (sorted-entries (sort srfi-233-IR comparator)))
> +    #~(string-append
> +       #$@(list-transduce ini-transducer rcons sorted-entries))))
> +

Please add doc strings to all new procedures.  I think comments in
Scheme are more commonly nested inside the procedure than on top of it,
like is custom in C, though that's mostly based on what I saw in Guix.

> +
> +;;;
> +;;; Serializers
> +;;;
> +
> +;; These are “gratuitous” serializers that can be readily used by
> +;; using the literal (prefix generic-ini-) within define-configuration.
> +

Instead of gratuitous, which sounds pejorative to me, I'd reword to
"Convenience serializers that can be ..."

> +;; Notes: field-name-transform can be used to “uglify” a field-name,
> +;; e.g. want-ipv6?  ->  want_ipv6
> +(define* (generic-ini-serialize-string field-name value #:key section
> +                                       (field-name-transform identity))
> +  (list section (field-name-transform field-name) value))
> +
> +(define* (generic-ini-serialize-boolean field-name value #:key section
> +                            (field-name-transform identity))
> +  (list section (field-name-transform field-name)
> +        (if value "true" "false")))
> +
> +(define (generic-ini-serialize-ini-entry field-name value)
> +  value)
> +
> +(define (generic-ini-serialize-list-of-ini-entries field-name value)
> +  (ini-entries value))

Here also, please add docstrings.

> diff --git a/tests/services/configuration/generic-ini.scm b/tests/services/configuration/generic-ini.scm
> new file mode 100644
> index 0000000000..797a01af31
> --- /dev/null
> +++ b/tests/services/configuration/generic-ini.scm
> @@ -0,0 +1,129 @@
> +;;; GNU Guix --- Functional package management for GNU
> +;;; Copyright © 2023 Bruno Victal <mirai@makinata.eu>
> +;;;
> +;;; This file is part of GNU Guix.
> +;;;
> +;;; GNU Guix is free software; you can redistribute it and/or modify it
> +;;; under the terms of the GNU General Public License as published by
> +;;; the Free Software Foundation; either version 3 of the License, or (at
> +;;; your option) any later version.
> +;;;
> +;;; GNU Guix is distributed in the hope that it will be useful, but
> +;;; WITHOUT ANY WARRANTY; without even the implied warranty of
> +;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +;;; GNU General Public License for more details.
> +;;;
> +;;; You should have received a copy of the GNU General Public License
> +;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
> +
> +(define-module (tests services configuration generic-ini)
> +  #:use-module (gnu services configuration)
> +  #:use-module (gnu services configuration generic-ini)
> +  #:use-module (guix diagnostics)
> +  #:use-module (guix gexp)
> +  #:use-module (guix store)
> +  #:autoload (guix i18n) (G_)

Are all these modules truly needed, e.g. the i18n one and (guix
diagnostics)?

> +  #:use-module (srfi srfi-34)
> +  #:use-module (srfi srfi-64)
> +  #:use-module (srfi srfi-71))
> +
> +;;; Tests for the (gnu services configuration generic-ini) module.
> +
> +(test-begin "generic-ini serializer")
> +
> +
> +(define expected-output "\
> +[guardians]
> +llamas=Tommy,Isabella
> +donkeys=Franz,Olly
> +
> +[ranch]
> +shepherd=Emma
> +
> +[shed]
> +colours=Alizarin
> +enabled=true
> +capacity=50
> +production=wool
> +
> +[vehicles]
> +cars=313
> +bikes=Amaryllis
> +")
> +
> +
> +;;;
> +;;; Serializers
> +;;;
> +(define (strip-trailing-?-character field-name)

nitpick: 'strip-trailing-?' seems explicit enough to me :-).

> +  "Drop rightmost '?' character"
> +  (let ((str (symbol->string field-name)))
> +    (if (string-suffix? "?" str)
> +        (string->symbol (string-drop-right str 1))
> +        field-name)))
> +
> +(define* (serialize-string field-name value #:key section)
> +  (list section field-name value))
> +
> +(define* (serialize-number field-name value #:key section)
> +  (list section field-name (number->string value)))
> +
> +(define* (serialize-boolean field-name value #:key section)
> +  (list section (strip-trailing-?-character field-name)
> +        (if value "true" "false")))
> +
> +(define serialize-ini-entry
> +  generic-ini-serialize-ini-entry)
> +
> +(define serialize-list-of-ini-entries
> +  generic-ini-serialize-list-of-ini-entries)
> +
> +
> +;;;
> +;;; Record-type definition
> +;;;
> +
> +(define-configuration foo-configuration
> +  (production
> +   (string "wool")
> +   "Lorem Ipsum …"
> +   (serializer-options '(#:section shed)))
> +
> +  (capacity
> +   (number 50)
> +   "Lorem Ipsum …"
> +   (serializer-options '(#:section shed)))
> +
> +  (enabled?
> +   (boolean #t)
> +   "Lorem Ipsum …"
> +   (serializer-options '(#:section shed)))
> +
> +  (shepherd
> +   (string "Emma")
> +   "Lorem Ipsum …"
> +   (serializer-options '(#:section ranch)))
> +
> +  (raw-entry
> +   (ini-entry '(shed colours "Alizarin"))
> +   "Lorem Ipsum …")
> +
> +  (escape-hatch
> +   (list-of-ini-entries '((vehicles bikes "Amaryllis")
> +                          (vehicles cars "313")
> +                          (guardians donkeys "Franz,Olly")
> +                          (guardians llamas "Tommy,Isabella")))
> +   "Lorem Ipsum …"))
> +
> +(test-equal "Well-formed INI output from serialize-ini"
> +  expected-output
> +  ;; Serialize the above into a string, properly resolving any potential
> +  ;; nested G-Exps as well.
> +  (let* ((serialized-ini
> +          (serialize-ini-configuration (foo-configuration)
> +                                       foo-configuration-fields))
> +         (lowered conn (with-store store
> +                         ((lower-gexp serialized-ini) store))))
> +    (eval (lowered-gexp-sexp lowered) (current-module))))
> +

Since 'conn' appears unused, I think you don't need to bind it at all,
and can then drop (srfi srfi-71).

--
Thanks,
Maxim