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guix/gnu/services/configuration.scm
Xinglu Chen 2ad896751c
services: configuration: Allow specifying prefix for serializer names. 
Sometimes two configurations might have the same types for their field values,
but the values might be serialized in two completely different
ways (e.g. because the two programs have different configuration languages).

An example of this would be the ‘serialize-boolean’ procedure in (gnu services
mail) and (gnu services getmail).  They both serialize a boolean value, but
because the Dovecot’s configuration language has a different syntax to the
configuration language for Getmail, two different procedures have to be
defined.

One way to workaround this would be to specify custom serializers for many
fields in order to separate the serialization of the values that have the same
type but serialize in different ways.  This could get very tedious, especially
if there are many configurations in the same module.

Another way would be to move one of the configurations to its own module, like
what was done with (gnu services getmail).  However, this would mean that
there would be multiple modules containing configurations for related
programs, e.g. we have (gnu services mail) and (gnu services getmail), it
doesn’t make much sense to keep the Getmail configuration in its own module.

This patch will allow one to write something like this:

  (define-configuration foo-configuration
    (bar
      (string "bob")
      "Option bar.")
    (prefix bar-))

and the value of the ‘bar’ field would be serialized using a procedure named
‘bar-serialize-string’ instead of just ‘serialize-string’.

* gnu/services/configuration.scm (define-maybe-helper): Accept ‘prefix’
argument for using serializer with custom prefix.
(define-maybe): Pattern match on ‘prefix’ literal.
(define-configuration-helper): Accept ‘prefix’ argument for using serializer
with custom prefix.
(define-configuration): Pattern match on ‘prefix’ literal.
* tests/services/configuration.scm ("serialize-configuration with prefix"):
New test.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>
2021-06-29 12:37:33 +02:00

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;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2015 Andy Wingo <wingo@igalia.com>
;;; Copyright © 2017 Mathieu Othacehe <m.othacehe@gmail.com>
;;; Copyright © 2017, 2018 Clément Lassieur <clement@lassieur.org>
;;; Copyright © 2021 Xinglu Chen <public@yoctocell.xyz>
;;; Copyright © 2021 Maxim Cournoyer <maxim.cournoyer@gmail.com>
;;;
;;; 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)
#:use-module (guix packages)
#:use-module (guix records)
#:use-module (guix gexp)
#:use-module ((guix utils) #:select (source-properties->location))
#:autoload (texinfo) (texi-fragment->stexi)
#:autoload (texinfo serialize) (stexi->texi)
#:use-module (ice-9 match)
#:use-module ((srfi srfi-1) #:select (append-map))
#:use-module (srfi srfi-34)
#:use-module (srfi srfi-35)
#:export (configuration-field
configuration-field-name
configuration-field-type
configuration-missing-field
configuration-field-error
configuration-field-serializer
configuration-field-getter
configuration-field-default-value-thunk
configuration-field-documentation
configuration-error?
define-configuration
define-configuration/no-serialization
no-serialization
serialize-configuration
define-maybe
define-maybe/no-serialization
validate-configuration
generate-documentation
configuration->documentation
empty-serializer
serialize-package))
;;; Commentary:
;;;
;;; Syntax for creating Scheme bindings to complex configuration files.
;;;
;;; Code:
(define-condition-type &configuration-error &error
configuration-error?)
(define (configuration-error message)
(raise (condition (&message (message message))
(&configuration-error))))
(define (configuration-field-error field val)
(configuration-error
(format #f "Invalid value for field ~a: ~s" field val)))
(define (configuration-missing-field kind field)
(configuration-error
(format #f "~a configuration missing required field ~a" kind field)))
(define (configuration-no-default-value kind field)
(configuration-error
(format #f "The field `~a' of the `~a' configuration record \
does not have a default value" field kind)))
(define-record-type* <configuration-field>
configuration-field make-configuration-field configuration-field?
(name configuration-field-name)
(type configuration-field-type)
(getter configuration-field-getter)
(predicate configuration-field-predicate)
(serializer configuration-field-serializer)
(default-value-thunk configuration-field-default-value-thunk)
(documentation configuration-field-documentation))
(define (serialize-configuration config fields)
#~(string-append
#$@(map (lambda (field)
((configuration-field-serializer field)
(configuration-field-name field)
((configuration-field-getter field) config)))
fields)))
(define (validate-configuration config fields)
(for-each (lambda (field)
(let ((val ((configuration-field-getter field) config)))
(unless ((configuration-field-predicate field) val)
(configuration-field-error
(configuration-field-name field) val))))
fields))
(define-syntax-rule (id ctx parts ...)
"Assemble PARTS into a raw (unhygienic) identifier."
(datum->syntax ctx (symbol-append (syntax->datum parts) ...)))
(define (define-maybe-helper serialize? prefix syn)
(syntax-case syn ()
((_ stem)
(with-syntax
((stem? (id #'stem #'stem #'?))
(maybe-stem? (id #'stem #'maybe- #'stem #'?))
(serialize-stem (if prefix
(id #'stem prefix #'serialize- #'stem)
(id #'stem #'serialize- #'stem)))
(serialize-maybe-stem (if prefix
(id #'stem prefix #'serialize-maybe- #'stem)
(id #'stem #'serialize-maybe- #'stem))))
#`(begin
(define (maybe-stem? val)
(or (eq? val 'disabled) (stem? val)))
#,@(if serialize?
(list #'(define (serialize-maybe-stem field-name val)
(if (stem? val)
(serialize-stem field-name val)
"")))
'()))))))
(define-syntax define-maybe
(lambda (x)
(syntax-case x (no-serialization prefix)
((_ stem (no-serialization))
(define-maybe-helper #f #f #'(_ stem)))
((_ stem (prefix serializer-prefix))
(define-maybe-helper #t #'serializer-prefix #'(_ stem)))
((_ stem)
(define-maybe-helper #t #f #'(_ stem))))))
(define-syntax-rule (define-maybe/no-serialization stem)
(define-maybe stem (no-serialization)))
(define (define-configuration-helper serialize? serializer-prefix syn)
(syntax-case syn ()
((_ stem (field (field-type def ...) doc custom-serializer ...) ...)
(with-syntax (((field-getter ...)
(map (lambda (field)
(id #'stem #'stem #'- field))
#'(field ...)))
((field-predicate ...)
(map (lambda (type)
(id #'stem type #'?))
#'(field-type ...)))
((field-default ...)
(map (match-lambda
((field-type default-value)
default-value)
((field-type)
;; Quote `undefined' to prevent a possibly
;; unbound warning.
(syntax 'undefined)))
#'((field-type def ...) ...)))
((field-serializer ...)
(map (lambda (type custom-serializer)
(and serialize?
(match custom-serializer
((serializer)
serializer)
(()
(if serializer-prefix
(id #'stem
serializer-prefix
#'serialize- type)
(id #'stem #'serialize- type))))))
#'(field-type ...)
#'((custom-serializer ...) ...))))
#`(begin
(define-record-type* #,(id #'stem #'< #'stem #'>)
#,(id #'stem #'% #'stem)
#,(id #'stem #'make- #'stem)
#,(id #'stem #'stem #'?)
(%location #,(id #'stem #'stem #'-location)
(default (and=> (current-source-location)
source-properties->location))
(innate))
#,@(map (lambda (name getter def)
(if (eq? (syntax->datum def) (quote 'undefined))
#`(#,name #,getter)
#`(#,name #,getter (default #,def))))
#'(field ...)
#'(field-getter ...)
#'(field-default ...)))
(define #,(id #'stem #'stem #'-fields)
(list (configuration-field
(name 'field)
(type 'field-type)
(getter field-getter)
(predicate field-predicate)
(serializer field-serializer)
(default-value-thunk
(lambda ()
(display '#,(id #'stem #'% #'stem))
(if (eq? (syntax->datum field-default)
'undefined)
(configuration-no-default-value
'#,(id #'stem #'% #'stem) 'field)
field-default)))
(documentation doc))
...))
(define-syntax-rule (stem arg (... ...))
(let ((conf (#,(id #'stem #'% #'stem) arg (... ...))))
(validate-configuration conf
#,(id #'stem #'stem #'-fields))
conf)))))))
(define no-serialization ;syntactic keyword for 'define-configuration'
'(no serialization))
(define-syntax define-configuration
(lambda (s)
(syntax-case s (no-serialization prefix)
((_ stem (field (field-type def ...) doc custom-serializer ...) ...
(no-serialization))
(define-configuration-helper
#f #f #'(_ stem (field (field-type def ...) doc custom-serializer ...)
...)))
((_ stem (field (field-type def ...) doc custom-serializer ...) ...
(prefix serializer-prefix))
(define-configuration-helper
#t #'serializer-prefix #'(_ stem (field (field-type def ...)
doc custom-serializer ...)
...)))
((_ stem (field (field-type def ...) doc custom-serializer ...) ...)
(define-configuration-helper
#t #f #'(_ stem (field (field-type def ...) doc custom-serializer ...)
...))))))
(define-syntax-rule (define-configuration/no-serialization
stem (field (field-type def ...)
doc custom-serializer ...) ...)
(define-configuration stem (field (field-type def ...)
doc custom-serializer ...) ...
(no-serialization)))
(define (empty-serializer field-name val) "")
(define serialize-package empty-serializer)
;; A little helper to make it easier to document all those fields.
(define (generate-documentation documentation documentation-name)
(define (str x) (object->string x))
(define (generate configuration-name)
(match (assq-ref documentation configuration-name)
((fields . sub-documentation)
`((para "Available " (code ,(str configuration-name)) " fields are:")
,@(map
(lambda (f)
(let ((field-name (configuration-field-name f))
(field-type (configuration-field-type f))
(field-docs (cdr (texi-fragment->stexi
(configuration-field-documentation f))))
(default (catch #t
(configuration-field-default-value-thunk f)
(lambda _ '%invalid))))
(define (show-default? val)
(or (string? val) (number? val) (boolean? val)
(and (symbol? val) (not (eq? val '%invalid)))
(and (list? val) (and-map show-default? val))))
`(deftypevr (% (category
(code ,(str configuration-name)) " parameter")
(data-type ,(str field-type))
(name ,(str field-name)))
,@field-docs
,@(if (show-default? default)
`((para "Defaults to " (samp ,(str default)) "."))
'())
,@(append-map
generate
(or (assq-ref sub-documentation field-name) '())))))
fields)))))
(stexi->texi `(*fragment* . ,(generate documentation-name))))
(define (configuration->documentation configuration-symbol)
"Take CONFIGURATION-SYMBOL, the symbol corresponding to the name used when
defining a configuration record with DEFINE-CONFIGURATION, and output the
Texinfo documentation of its fields."
;; This is helper for a simple, straight-forward application of
;; GENERATE-DOCUMENTATION.
(let ((fields-getter (module-ref (current-module)
(symbol-append configuration-symbol
'-fields))))
(display (generate-documentation `((,configuration-symbol ,fields-getter))
configuration-symbol))))
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