Subject: [PATCH] guix: records: Improve error reporting.

From: Julien Lepiller <[email-masked]>
Date: Wed, 21 Jul 2021 01:40:47 +0200

Hi Guix!

This patch improves error reporting a bit when making mistakes in guix
records. This is motivated by a user getting "invalid field specifier"
for their whole services field in their os record. With this patches,
they would have seen:

multiple values in field specifier. Got 2 values associated with key
services. Values are:
(append (list (service ...) ...))
(modify-services %desktop-services ...)

Which would have hinted them at fixing the parenthesis. Or at least, it
would have saved us some time trying to count them :)

Here are the cases that are handled and the associated message:

(operating-system
  services)
guix system: error: services: invalid field specifier. The format of a
field is `(services value)'

(operating-system
  (services))
test.scm:2:2: error: (services): Value missing in field specifier. The
format of a field is `(services value)'.

(operating-system
  (services 1 2 3))
test.scm:2:2: error: (services 1 2 3): multiple values in field
specifier. Got 3 values associated with key services. Values are:
1
2
3

(operating-system
  ())
guix system: error: (): invalid field specifier. The format of a field
is `(field value)'

(operating-system
  ((services %desktop-services)))
test.scm:2:2: error: ((services %desktop-services)): invalid field
specifier. (services %desktop-services) is not a valid field name.

Of course, we can improve these error messages, and internationalize
them.

WDYT?
From 4cde5555682ca6a3c78cb274cc308087e51ea0e9 Mon Sep 17 00:00:00 2001
From: Julien Lepiller <[email-masked]>
Date: Wed, 21 Jul 2021 01:30:04 +0200
Subject: [PATCH] guix: records: Improve error reporting.

* guix/records.scm (report-invalid-field-specifier): Handle various
invalidity causes separately.
---
 guix/records.scm | 37 ++++++++++++++++++++++++++++++++++---
 1 file changed, 34 insertions(+), 3 deletions(-)

diff --git a/guix/records.scm b/guix/records.scm
index 3d54a51956..3c3dd478a5 100644
--- a/guix/records.scm
+++ b/guix/records.scm
@@ -1,6 +1,7 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020 Ludovic Courtès <[email-masked]>
 ;;; Copyright © 2018 Mark H Weaver <[email-masked]>
+;;; Copyright © 2021 Julien Lepiller <[email-masked]>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -83,10 +84,40 @@ error-reporting purposes."
          ;; WEIRD may be an identifier, thus lacking source location info, and
          ;; BINDINGS is a list, also lacking source location info.  Hopefully
          ;; PARENT-FORM provides source location info.
-         (apply syntax-violation name "invalid field specifier"
-                (if parent-form
+         (syntax-case #'weird ()
+           (()                             ;the empty list
+             (apply syntax-violation name
+                    "invalid field specifier. The format of a field is `(field value)'"
                     (list parent-form #'weird)
-                    (list #'weird)))))))
+                    (list #'weird)))
+           (((field ...) _ ...)            ;a list whose first element is a list
+            (apply syntax-violation name
+                   (format #f "invalid field specifier. ~a is not a valid field name."
+                           (map syntax->datum #'(field ...)))
+                   (list parent-form #'weird)
+                   (list #'weird)))
+           ((field)                        ;a list with one element
+            (apply syntax-violation name
+                   (format #f "Value missing in field specifier. The format of \
+a field is `(~a value)'."
+                           (syntax->datum #'field))
+                   (list parent-form #'weird)
+                   (list #'weird)))
+           ((field value ...)              ;any other list
+            (apply syntax-violation name
+                   (format #f "multiple values in field specifier. Got ~a values \
+associated with key ~a. Values are:~%~{~a~%~}"
+                           (length #'(value ...)) (syntax->datum #'field)
+                           (map syntax->datum #'(value ...)))
+                    (list parent-form #'weird)
+                    (list #'weird)))
+           (field                          ;not a list
+             (apply syntax-violation name
+                    (format #f "invalid field specifier. The format of a field \
+is `(~a value)'"
+                            (syntax->datum #'field))
+                    (list parent-form #'weird)
+                    (list #'weird))))))))
 
   (define (report-duplicate-field-specifier name ctor)
     "Report the first duplicate identifier among the bindings in CTOR."
-- 
2.32.0