Subject: [bug#65352] [PATCH v2] DRAFT git: Avoid touching the network unless needed in 'reference-available?'.

From: Simon Tournier <[email-masked]>
Date: Wed, 6 Sep 2023 16:17:08 +0200

Follow-up of 756e336fa008c2469b4a7317ad5c641ed48f25d6 fixing the issue.

* guix/git/scm (reference-available?): Address case by case to determine
whether the reference exists in the local Git checkout.
---
 guix/git.scm | 22 +++++++++-------------
 1 file changed, 9 insertions(+), 13 deletions(-)

Hi,

Here a draft about what I think is the correct solution.

Well, the tests we have talked about are all passing.

Let me know what you think.

Cheers,
simon

diff --git a/guix/git.scm b/guix/git.scm
index 1cb87a45607b..1b3355109e42 100644
--- a/guix/git.scm
+++ b/guix/git.scm
@@ -5,6 +5,7 @@
 ;;; Copyright © 2021 Marius Bakke <[email-masked]>
 ;;; Copyright © 2022 Maxime Devos <[email-masked]>
 ;;; Copyright © 2023 Tobias Geerinckx-Rice <[email-masked]>
+;;; Copyright © 2023 Simon Tournier <[email-masked]>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -360,21 +361,16 @@ (define-syntax-rule (false-if-git-not-found exp)
 (define (reference-available? repository ref)
   "Return true if REF, a reference such as '(commit . \"cabba9e\"), is
 definitely available in REPOSITORY, false otherwise."
-  ;; Note: this must not rely on 'resolve-reference', as that procedure always
-  ;; resolves the references for branch names such as master.  The semantic we
-  ;; want here is that unless the reference is exact (e.g. a commit), the
-  ;; reference should not be considered available, as it could have changed on
-  ;; the remote.
   (match ref
-    ((or ('commit . commit)
-         ('tag-or-commit . (? commit-id? commit)))
-     (let ((len (string-length commit))
-           (oid (string->oid commit)))
-       (false-if-git-not-found
-        (->bool (if (< len 40)
-                    (object-lookup-prefix repository oid len OBJ-COMMIT)
-                    (commit-lookup repository oid))))))
+    (('commit . (? commit-id? commit))
+     (let ((oid (string->oid commit)))
+       (->bool (commit-lookup repository oid))))
+    ((or ('tag . str)
+         ('tag-or-commit . str))
+     (false-if-git-not-found
+      (->bool (resolve-reference repository ref))))
     (_
+     ;; For the others REF as branch or symref, the REF cannot be available
      #f)))
 
 (define (clone-from-swh url tag-or-commit output)

base-commit: 6113e0529d61df7425f64e30a6bf77f7cfdfe5a5
-- 
2.38.1