Subject: bug#49081: 28.0.50; [PATCH] Feature suggestion, Gnus summary mode sorting for extra headers

From: Alex Bochannek <[email-masked]>
Date: Sat, 19 Jun 2021 12:08:55 -0700

Lars Ingebrigtsen <[email-masked]> writes:

> Alex Bochannek <[email-masked]> writes:
>
>> Since I was able to get the Newsgroups extra header working for
>> `nnvirtual' groups, I would like to not only limit, but also sort by the
>> extra headers.
>
> Looks good; applied with one minor tweak:
>
>> +(defun gnus-article-sort-by-newsgroups (h1 h2)
>> +  "Sort articles by newsgroups."
>> +  (gnus-string<
>> +   (let ((extract (funcall
>> +		   gnus-extract-address-components
>> +		   (or (cdr (assq 'Newsgroups (mail-header-extra h1))) ""))))
>> +     (or (car extract) (cadr extract)))
>> +   (let ((extract (funcall
>> +		   gnus-extract-address-components
>> +		   (or (cdr (assq 'Newsgroups (mail-header-extra h2))) ""))))
>> +     (or (car extract) (cadr extract)))))
>
> I rewrote that to:
>
> (defun gnus-article-sort-by-newsgroups (h1 h2)
>   "Sort articles by newsgroups."
>   (let ((ex
>          (lambda (h)
>            (let ((extract
>                   (funcall gnus-extract-address-components
> 		           (or (cdr (assq 'Newsgroups (mail-header-extra h)))
>                                ""))))
>              (or (car extract) (cadr extract))))))
>     (gnus-string< (funcall ex h1) (funcall ex h2))))
>
> To avoid the duplication -- let me know if I messed up that bit.

Looks good, thank you!

I originally had duplicated that code from
`gnus-article-sort-by-recipient' and it's probably a good idea to make
that into a utility function.
diff --git a/lisp/gnus/gnus-sum.el b/lisp/gnus/gnus-sum.el
index 908c10c11d..788676c7c8 100644
--- a/lisp/gnus/gnus-sum.el
+++ b/lisp/gnus/gnus-sum.el
@@ -5085,15 +5085,10 @@ gnus-thread-sort-by-author
 
 (defsubst gnus-article-sort-by-recipient (h1 h2)
   "Sort articles by recipient."
-  (gnus-string<
-   (let ((extract (funcall
-		   gnus-extract-address-components
-		   (or (cdr (assq 'To (mail-header-extra h1))) ""))))
-     (or (car extract) (cadr extract)))
-   (let ((extract (funcall
-		   gnus-extract-address-components
-		   (or (cdr (assq 'To (mail-header-extra h2))) ""))))
-     (or (car extract) (cadr extract)))))
+  (let ((ex
+	 (lambda (h)
+	   (gnus-article-sort-extract-extra 'To h))))
+    (gnus-string< (funcall ex h1) (funcall ex h2))))
 
 (defun gnus-thread-sort-by-recipient (h1 h2)
   "Sort threads by root recipient."
@@ -5188,15 +5183,11 @@ gnus-thread-sort-by-most-recent-date
   "Sort threads such that the thread with the most recently dated article comes first."
   (> (gnus-thread-latest-date h1) (gnus-thread-latest-date h2)))
 
-(defun gnus-article-sort-by-newsgroups (h1 h2)
+(defsubst gnus-article-sort-by-newsgroups (h1 h2)
   "Sort articles by newsgroups."
   (let ((ex
-         (lambda (h)
-           (let ((extract
-                  (funcall gnus-extract-address-components
-		           (or (cdr (assq 'Newsgroups (mail-header-extra h)))
-                               ""))))
-             (or (car extract) (cadr extract))))))
+	 (lambda (h)
+	   (gnus-article-sort-extract-extra 'Newsgroups h))))
     (gnus-string< (funcall ex h1) (funcall ex h2))))
 
 (defun gnus-thread-sort-by-newsgroups (h1 h2)
@@ -5204,6 +5195,12 @@ gnus-thread-sort-by-newsgroups
   (gnus-article-sort-by-newsgroups
    (gnus-thread-header h1) (gnus-thread-header h2)))
 
+(defsubst gnus-article-sort-extract-extra (Name header)
+    (let ((extract
+	   (funcall gnus-extract-address-components
+		    (or (cdr (assq name (mail-header-extra header)))
+			""))))
+      (or (car extract) (cadr extract))))
 
 ; Since this is called not only to sort the top-level threads, but
 ; also in recursive sorts to order the articles within a thread, each
A similar pattern is used by `gnus-article-sort-by-author', but I didn't
see an easy way to unify these without also passing around functions by
header type.

Also, I haven't used `defsubst' before, so I leave it up to you if it
makes sense to use that for the `gnus-article-sort-by-newsgroups' and
`gnus-article-sort-by-newsgroups', respectively.

Thanks!

-- 
Alex.