records: Let thunked fields refer to their inherited value.

* guix/records.scm (make-syntactic-constructor)[field-index]: New procedure.
[wrap-field-value]: Add optional argument ‘parent’.  When it is true, bind F
to the inherited field value.
[field-bindings/inheritance]: New procedure.
Use it.
* tests/records.scm ("define-record-type* & thunked & no inherited value")
("define-record-type* & thunked & inherited value")
("define-record-type* & thunked & inherited value & this-record"): New tests.
* doc/guix.texi (Defining Package Variants): Update ‘modify-inputs’ example to
refer to ‘inputs’.
(Writing Manifests): Likewise.
* doc/guix-cookbook.texi (Package Variants): Likewise for
‘substitute-keyword-arguments’.

Fixes: https://issues.guix.gnu.org/50335
Change-Id: If4e18155ce203637ff9e116ee8098f8997bfebe2

2 files changed, 8 insertions, 7 deletions

diff --git a/doc/guix-cookbook.texi b/doc/guix-cookbook.texi
index 4b6f0ca22c0..83bce66c175 100644
--- a/doc/guix-cookbook.texi
+++ b/doc/guix-cookbook.texi
@@ -5297,7 +5297,7 @@ did above with transformation options. We can add them like so:
   "Return P with FLAGS as additional 'configure' flags."
   (package/inherit p
     (arguments
-     (substitute-keyword-arguments (package-arguments p)
+     (substitute-keyword-arguments arguments
        ((#:configure-flags original-flags #~(list))
         #~(append #$original-flags #$flags))))))
 
diff --git a/doc/guix.texi b/doc/guix.texi
index e7bcd174a8e..d5f782f35c4 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -8800,14 +8800,15 @@ dependency like so:
 (define gdb-sans-guile
   (package
     (inherit gdb)
-    (inputs (modify-inputs (package-inputs gdb)
+    (inputs (modify-inputs inputs
               (delete "guile")))))
 @end lisp
 
-The @code{modify-inputs} form above removes the @code{"guile"} package
-from the @code{inputs} field of @code{gdb}.  The @code{modify-inputs}
-macro is a helper that can prove useful anytime you want to remove, add,
-or replace package inputs.
+In the body of the @code{inputs} field above, @code{inputs} is bound to
+the inherited value.  Thus, the @code{modify-inputs} form above removes
+the @code{"guile"} package from the @code{inputs} field of @code{gdb}.
+The @code{modify-inputs} macro is a helper that can prove useful anytime
+you want to remove, add, or replace package inputs.
 
 @defmac modify-inputs inputs clauses
 Modify the given package inputs, as returned by @code{package-inputs} & co.,
@@ -9131,7 +9132,7 @@ these lines:
 (define gdb-sans-guile
   (package
     (inherit gdb)
-    (inputs (modify-inputs (package-inputs gdb)
+    (inputs (modify-inputs inputs
               (delete "guile")))))
 
 ;; Return a manifest containing that one package plus Git.