[bug#57496] [PATCH v3 3/3] gnu: bootloader: Add a friendly error message of menu-entry.

[typ22]

From: tiantian <typ22@foxmail.com>

* gnu/bootloader.scm (report-menu-entry-error): New procedure.
(menu-entry->sexp): Modify the pattern and add `else' to call
`report-menu-entry-error'.

Co-Authored-By: Julien Lepiller <julien@lepiller.eu>
---
The error message like so:

guix system: error: invalid menu-entry: #<<menu-entry> label: "test" device: 
#<file-system-label "guix-root"> device-mount-point: #f linux: #f 
linux-arguments: () initrd: #f multiboot-kernel: #f multiboot-arguments: () 
multiboot-modules: () chain-loader: #f>
hint: Please chose only one of:

  1. direct boot by specifying fields `linux', `linux-arguments' and 
`linux-modules',

  2. multiboot by specifying fields `multiboot-kernel', `multiboot-arguments' 
and `multiboot-modules',

  3. chain-loader by specifying field `chain-loader'.

The code of `report-menu-entry-error' is quoted from Julien Lepiller.
Thanks the help from Julien Lepiller.

 gnu/bootloader.scm | 44 +++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 39 insertions(+), 5 deletions(-)

diff --git a/gnu/bootloader.scm b/gnu/bootloader.scm
index 9e8b545d10..d4fe460570 100644
--- a/gnu/bootloader.scm
+++ b/gnu/bootloader.scm
@@ -34,6 +34,8 @@ (define-module (gnu bootloader)
   #:use-module (guix diagnostics)
   #:use-module (guix i18n)
   #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-34)
+  #:use-module (srfi srfi-35)
   #:use-module (ice-9 match)
   #:export (menu-entry
             menu-entry?
@@ -110,6 +112,23 @@ (define-record-type* <menu-entry>
   (chain-loader     menu-entry-chain-loader
                     (default #f)))         ; string, path of efi file
 
+(define (report-menu-entry-error menu-entry)
+  (raise
+   (condition
+    (&message
+     (message
+      (format #f (G_ "invalid menu-entry: ~a") menu-entry)))
+    (&fix-hint
+     (hint
+      (G_ "Please chose only one of:
+@enumerate
+@item direct boot by specifying fields @code{linux},
+@code{linux-arguments} and @code{linux-modules},
+@item multiboot by specifying fields @code{multiboot-kernel},
+@code{multiboot-arguments} and @code{multiboot-modules},
+@item chain-loader by specifying field @code{chain-loader}.
+@end enumerate"))))))
+
 (define (menu-entry->sexp entry)
   "Return ENTRY serialized as an sexp."
   (define (device->sexp device)
@@ -119,9 +138,21 @@ (define (menu-entry->sexp entry)
       ((? file-system-label? label)
        `(label ,(file-system-label->string label)))
       (_ device)))
+  (define (set-field? field)
+    "If the field is the default value, return #f."
+    (and field                  ; not default value #f
+         (not (null? field))))  ; not default value '()
   (match entry
+    ;; Modify the pattern to achieve more strict matching and prevent
+    ;; wrong matching, which ensures the output of error information
+    ;; when menu-entry is wrong.
+
+    ;; The linux-arguments is optional and the test code for boot-parameters
+    ;; does not set it, so don't check it here.
     (($ <menu-entry> label device mount-point
-                     (? identity linux) linux-arguments initrd
+                     (? set-field? linux)
+                     linux-arguments
+                     (? set-field? initrd)
                      #f () () #f)
      `(menu-entry (version 0)
                   (label ,label)
@@ -131,8 +162,10 @@ (define (menu-entry->sexp entry)
                   (linux-arguments ,linux-arguments)
                   (initrd ,initrd)))
     (($ <menu-entry> label device mount-point #f () #f
-                     (? identity multiboot-kernel) multiboot-arguments
-                     multiboot-modules #f)
+                     (? set-field? multiboot-kernel)
+                     (? set-field? multiboot-arguments)
+                     (? set-field? multiboot-modules)
+                     #f)
      `(menu-entry (version 0)
                   (label ,label)
                   (device ,(device->sexp device))
@@ -141,12 +174,13 @@ (define (menu-entry->sexp entry)
                   (multiboot-arguments ,multiboot-arguments)
                   (multiboot-modules ,multiboot-modules)))
     (($ <menu-entry> label device mount-point #f () #f #f () ()
-                     (? identity chain-loader))
+                     (? set-field? chain-loader))
      `(menu-entry (version 0)
                   (label ,label)
                   (device ,(device->sexp device))
                   (device-mount-point ,mount-point)
-                  (chain-loader ,chain-loader)))))
+                  (chain-loader ,chain-loader)))
+    (else (report-menu-entry-error entry))))
 
 (define (sexp->menu-entry sexp)
   "Turn SEXP, an sexp as returned by 'menu-entry->sexp', into a <menu-entry>
-- 
2.37.2