services: configuration: Report the location of field type errors.

Previously field type errors would be reported in a non-standard way,
and without any source location information.  This fixes it.

* gnu/services/configuration.scm (configuration-field-error): Add a
'loc' parameter and honor it.  Use 'formatted-message' instead of plain
'format'.
(define-configuration-helper)[field-sanitizer]: New procedure.
Use it.  Use STEM as the identifier of the syntactic constructor of the
record type.  Add a 'sanitize' property to each field.  Remove now
useless STEM macro that would call 'validate-configuration'.
* gnu/services/mail.scm (serialize-listener-configuration): Adjust to
new 'configuration-field-error' prototype.
* tests/services/configuration.scm ("wrong type for a field"): New test.
* po/guix/POTFILES.in: Add gnu/services/configuration.scm.

gnu/services/configuration.scm

@@ -27,7 +27,8 @@
   #:use-module (guix records)
   #:use-module (guix gexp)
   #:use-module ((guix utils) #:select (source-properties->location))
-  #:use-module ((guix diagnostics) #:select (formatted-message location-file))
+  #:use-module ((guix diagnostics)
+                #:select (formatted-message location-file &error-location))
   #:use-module ((guix modules) #:select (file-name->module-name))
   #:use-module (guix i18n)
   #:autoload   (texinfo) (texi-fragment->stexi)
@@ -87,9 +88,17 @@
 (define (configuration-error message)
   (raise (condition (&message (message message))
                     (&configuration-error))))
-(define (configuration-field-error field val)
+(define (configuration-field-error loc field value)
-  (configuration-error
+  (raise (apply
-   (format #f "Invalid value for field ~a: ~s" field val)))
+          make-compound-condition
+          (formatted-message (G_ "invalid value ~s for field '~a'")
+                             value field)
+          (condition (&configuration-error))
+          (if loc
+              (list (condition
+                     (&error-location (location loc))))
+              '()))))
+
 (define (configuration-missing-field kind field)
   (configuration-error
    (format #f "~a configuration missing required field ~a" kind field)))
@@ -210,9 +219,33 @@ does not have a default value" field kind)))
                                 (id #'stem #'serialize- type))))))
                   #'(field-type ...)
                   #'((custom-serializer ...) ...))))
+         (define (field-sanitizer name pred)
+           ;; Define a macro for use as a record field sanitizer, where NAME
+           ;; is the name of the field and PRED is the predicate that tells
+           ;; whether a value is valid for this field.
+           #`(define-syntax #,(id #'stem #'validate- #'stem #'- name)
+               (lambda (s)
+                 ;; Make sure the given VALUE, for field NAME, passes PRED.
+                 (syntax-case s ()
+                   ((_ value)
+                    (with-syntax ((name #'#,name)
+                                  (pred #'#,pred)
+                                  (loc (datum->syntax #'value
+                                                      (syntax-source #'value))))
+                      #'(if (pred value)
+                            value
+                            (configuration-field-error
+                             (and=> 'loc source-properties->location)
+                             'name value))))))))
+
          #`(begin
+             ;; Define field validation macros.
+             #,@(map field-sanitizer
+                     #'(field ...)
+                     #'(field-predicate ...))
+
              (define-record-type* #,(id #'stem #'< #'stem #'>)
-               #,(id #'stem #'% #'stem)
+               stem
                #,(id #'stem #'make- #'stem)
                #,(id #'stem #'stem #'?)
                (%location #,(id #'stem #'stem #'-location)
@@ -220,10 +253,13 @@ does not have a default value" field kind)))
                                           source-properties->location))
                           (innate))
                #,@(map (lambda (name getter def)
-                         #`(#,name #,getter (default #,def)))
+                         #`(#,name #,getter (default #,def)
+                                   (sanitize
+                                    #,(id #'stem #'validate- #'stem #'- name))))
                        #'(field ...)
                        #'(field-getter ...)
                        #'(field-default ...)))
+
              (define #,(id #'stem #'stem #'-fields)
                (list (configuration-field
                       (name 'field)
@@ -240,12 +276,7 @@ does not have a default value" field kind)))
                                '#,(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))

gnu/services/mail.scm

@@ -285,7 +285,7 @@ the section name.")
     (serialize-fifo-listener-configuration field-name val))
    ((inet-listener-configuration? val)
     (serialize-inet-listener-configuration field-name val))
-   (else (configuration-field-error field-name val))))
+   (else (configuration-field-error #f field-name val))))
 (define (listener-configuration-list? val)
   (and (list? val) (and-map listener-configuration? val)))
 (define (serialize-listener-configuration-list field-name val)

po/guix/POTFILES.in

@@ -4,6 +4,7 @@ gnu.scm
 gnu/packages.scm
 gnu/services.scm
 gnu/system.scm
+gnu/services/configuration.scm
 gnu/services/shepherd.scm
 gnu/home/services.scm
 gnu/home/services/ssh.scm

tests/services/configuration.scm

@@ -1,6 +1,7 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2021 Maxim Cournoyer <maxim.cournoyer@gmail.com>
 ;;; Copyright © 2021 Xinglu Chen <public@yoctocell.xyz>
+;;; Copyright © 2022 Ludovic Courtès <ludo@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -19,6 +20,7 @@
 
 (define-module (tests services configuration)
   #:use-module (gnu services configuration)
+  #:use-module (guix diagnostics)
   #:use-module (guix gexp)
   #:use-module (srfi srfi-34)
   #:use-module (srfi srfi-64))
@@ -43,6 +45,17 @@
   80
   (port-configuration-port (port-configuration)))
 
+(test-equal "wrong type for a field"
+  '("configuration.scm" 57 11)                    ;error location
+  (guard (c ((configuration-error? c)
+             (let ((loc (error-location c)))
+               (list (basename (location-file loc))
+                     (location-line loc)
+                     (location-column loc)))))
+    (port-configuration
+     ;; This is line 56; the test relies on line/column numbers!
+     (port "This is not a number!"))))
+
 (define-configuration port-configuration-cs
   (port (number 80) "The port number." empty-serializer))