[bug#63135] [PATCH 1/3] records: match-record: Raise a syntax error if TYPE is nonexistent.

[(]

* guix/records.scm (match-record): Raise a human-compherensible syntax error
  if the given record type identifier is unbound.

Co-authored-by: Josselin Poiret <dev@jpoiret.xyz>
---
 guix/records.scm | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/guix/records.scm b/guix/records.scm
index 7d43b064d8..d8966998c1 100644
--- a/guix/records.scm
+++ b/guix/records.scm
@@ -105,7 +105,12 @@ (define (report-duplicate-field-specifier name ctor)
 
 (define-syntax map-fields
   (lambda (x)
-    (syntax-violation 'map-fields "bad use of syntactic keyword" x x)))
+    (syntax-case x ()
+      ((_ type within)
+       (syntax-violation (syntax->datum #'within)
+                         "undefined guix record-type"
+                         #'type))
+      (_ (syntax-violation 'map-fields "bad use of syntactic keyword" x x)))))
 
 (define-syntax-parameter this-record
   (lambda (s)
@@ -459,7 +464,7 @@ (define-syntax type
                    "This macro lets us query record type info at
 macro-expansion time."
                    (syntax-case s (map-fields)
-                     ((_ map-fields macro)
+                     ((_ (map-fields _ _) macro)
                       #'(macro (field ...)))
                      (id
                       (identifier? #'id)
@@ -595,7 +600,7 @@ (define-syntax match-record-inner
        #'(let-syntax ((field-offset (syntax-rules ()
                                      ((_ f)
                                        (lookup-field field 0 f)))))
-           (let* ((offset (type map-fields field-offset))
+           (let* ((offset (type (map-fields type match-record) field-offset))
                   (variable (struct-ref record offset)))
              (match-record-inner record type (rest ...) body ...))))
       ((_ record type (field rest ...) body ...)

base-commit: d59b4764f3171b1430a6d3b954659b8aab730475
-- 
2.39.2