From 6d6d897b5454e9fad50e373e8051cbe1c81e495a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ludovic=20Court=C3=A8s?= <ludo@gnu.org>
Date: Wed, 14 May 2025 22:05:02 +0200
Subject: [PATCH] =?UTF-8?q?channels:=20Speed=20up=20=E2=80=98channel-news-?=
 =?UTF-8?q?for-commit=E2=80=99.?=
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Partly fixes <https://issues.guix.gnu.org/78194>.

This makes the wall-clock time of:

  guix pull --list-generations > /dev/null

shrink from 33s to 4s on a profile with 8 generations.

* guix/channels.scm (channel-news-for-commit): Rewrite in terms of
‘commit-descendant?’.

Reported-by: Ian Eure <ian@retrospec.tv>
Change-Id: I387e3dc37437e2d98bfd7ab710417f68d16146ad
---
 guix/channels.scm | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/guix/channels.scm b/guix/channels.scm
index 7a02d24a846a84b85a3b6a43c25789ccdd5c24db..f6b3f40cc35cc9692511fa61a3ccc359b9296948 100644
--- a/guix/channels.scm
+++ b/guix/channels.scm
@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2018-2024 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2018-2025 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2018 Ricardo Wurmus <rekado@elephly.net>
 ;;; Copyright © 2019 Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
 ;;; Copyright © 2021 Brice Waegeneire <brice@waegenei.re>
@@ -31,7 +31,7 @@
   #:autoload   (git structs) (git-error-code)
   #:autoload   (guix git) (update-cached-checkout
                            url+commit->name
-                           commit-difference
+                           commit-descendant?
                            repository-info
                            commit-short-id
                            tag->commit
@@ -48,7 +48,6 @@
   #:use-module (guix progress)
   #:use-module (guix derivations)
   #:use-module (guix diagnostics)
-  #:use-module (guix sets)
   #:use-module (guix store)
   #:use-module (guix i18n)
   #:use-module (srfi srfi-1)
@@ -1237,15 +1236,16 @@ NEW.  When OLD is omitted or is #f, return all the news entries of CHANNEL."
                                                                      entry))
                                    (channel-news-entries news))))
                 (if old
-                    (let* ((new     (commit-lookup repository (string->oid new)))
-                           (old     (commit-lookup repository (string->oid old)))
-                           (commits (list->set
-                                     (map (compose oid->string commit-id)
-                                          (commit-difference new old)))))
-                      (filter (lambda (entry)
-                                (set-contains? commits
-                                               (channel-news-entry-commit entry)))
-                              entries))
+                    (let ((new (commit-lookup repository (string->oid new)))
+                          (old (commit-lookup repository (string->oid old))))
+                      (take-while (lambda (entry)
+                                    (let ((entry (commit-lookup
+                                                  repository
+                                                  (string->oid
+                                                   (channel-news-entry-commit entry)))))
+                                      (and (commit-descendant? new (list entry))
+                                           (not (commit-descendant? old (list entry))))))
+                                  entries))
                     entries)))
             '())))
     (lambda (key error . rest)