From 873f6f1334ab06a69e768a8aea0054404237542f Mon Sep 17 00:00:00 2001
From: Ludovic Courtès <ludo@gnu.org>
Date: Sat, 14 Sep 2019 17:54:06 +0200
Subject: git: Add 'commit-difference'.

* guix/git.scm (commit-closure, commit-difference): New procedures.
* guix/tests/git.scm, tests/git.scm: New files.
* Makefile.am (dist_noinst_DATA): Add guix/tests/git.scm.
(SCM_TESTS): Add tests/git.scm.
---
 guix/git.scm | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

(limited to 'guix/git.scm')

diff --git a/guix/git.scm b/guix/git.scm
index 92a7353b5a..d7dddde3a7 100644
--- a/guix/git.scm
+++ b/guix/git.scm
@@ -28,6 +28,7 @@
   #:use-module (guix utils)
   #:use-module (guix records)
   #:use-module (guix gexp)
+  #:use-module (guix sets)
   #:use-module (rnrs bytevectors)
   #:use-module (ice-9 match)
   #:use-module (srfi srfi-1)
@@ -37,8 +38,10 @@
   #:export (%repository-cache-directory
             honor-system-x509-certificates!
 
+            with-repository
             update-cached-checkout
             latest-repository-commit
+            commit-difference
 
             git-checkout
             git-checkout?
@@ -339,6 +342,43 @@ Log progress and checkout info to LOG-PORT."
 
 (set-exception-printer! 'git-error print-git-error)
 
+
+;;;
+;;; Commit difference.
+;;;
+
+(define (commit-closure commit)
+  "Return the closure of COMMIT as a set."
+  (let loop ((commits (list commit))
+             (visited (setq)))
+    (match commits
+      (()
+       visited)
+      ((head . tail)
+       (if (set-contains? visited head)
+           (loop tail visited)
+           (loop (append (commit-parents head) tail)
+                 (set-insert head visited)))))))
+
+(define (commit-difference new old)
+  "Return the list of commits between NEW and OLD, where OLD is assumed to be
+an ancestor of NEW.
+
+Essentially, this computes the set difference between the closure of NEW and
+that of OLD."
+  (let loop ((commits (list new))
+             (result '())
+             (visited (commit-closure old)))
+    (match commits
+      (()
+       (reverse result))
+      ((head . tail)
+       (if (set-contains? visited head)
+           (loop tail result visited)
+           (loop (append (commit-parents head) tail)
+                 (cons head result)
+                 (set-insert head visited)))))))
+
 
 ;;;
 ;;; Checkouts.
-- 
cgit v1.2.3