[bug#49181] [PATCH 1/1] guix: Make modify-phases error when adding before/after a missing phase

[Leo Prikler <leo.prikler@student.tugraz.at>]

From: Carlo Zancanaro <carlo@zancanaro.id.au>

* guix/build/utils.scm (alist-cons-before, alist-cons-after): Cause a match failure if the
reference is not found, rather than appending to the alist.
* tests/build-utils.scm: Update tests to match.
---
 guix/build/utils.scm  | 15 +++++++++------
 tests/build-utils.scm | 12 ++++++------
 2 files changed, 15 insertions(+), 12 deletions(-)

diff --git a/guix/build/utils.scm b/guix/build/utils.scm
index 419c10195b..6e052a7ea1 100644
--- a/guix/build/utils.scm
+++ b/guix/build/utils.scm
@@ -5,6 +5,7 @@
 ;;; Copyright © 2015, 2018 Mark H Weaver <mhw@netris.org>
 ;;; Copyright © 2018 Arun Isaac <arunisaac@systemreboot.net>
 ;;; Copyright © 2018, 2019 Ricardo Wurmus <rekado@elephly.net>
+;;; Copyright © 2021 Carlo Zancanaro <carlo@zancanaro.id.au>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -571,18 +572,22 @@ effects, such as displaying warnings or error messages."
 (define* (alist-cons-before reference key value alist
                             #:optional (key=? equal?))
   "Insert the KEY/VALUE pair before the first occurrence of a pair whose key
-is REFERENCE in ALIST.  Use KEY=? to compare keys."
+is REFERENCE in ALIST.  Use KEY=? to compare keys.  An error is raised when no
+such pair exists."
   (let-values (((before after)
                 (break (match-lambda
                         ((k . _)
                          (key=? k reference)))
                        alist)))
-    (append before (alist-cons key value after))))
+    (match after
+      ((reference after ...)
+       (append before (alist-cons key value (cons reference after)))))))
 
 (define* (alist-cons-after reference key value alist
                            #:optional (key=? equal?))
   "Insert the KEY/VALUE pair after the first occurrence of a pair whose key
-is REFERENCE in ALIST.  Use KEY=? to compare keys."
+is REFERENCE in ALIST.  Use KEY=? to compare keys.  An error is raised when
+no such pair exists."
   (let-values (((before after)
                 (break (match-lambda
                         ((k . _)
@@ -590,9 +595,7 @@ is REFERENCE in ALIST.  Use KEY=? to compare keys."
                        alist)))
     (match after
       ((reference after ...)
-       (append before (cons* reference `(,key . ,value) after)))
-      (()
-       (append before `((,key . ,value)))))))
+       (append before (cons* reference `(,key . ,value) after))))))
 
 (define* (alist-replace key value alist #:optional (key=? equal?))
   "Replace the first pair in ALIST whose car is KEY with the KEY/VALUE pair.
diff --git a/tests/build-utils.scm b/tests/build-utils.scm
index 654b480ed9..c694b479b3 100644
--- a/tests/build-utils.scm
+++ b/tests/build-utils.scm
@@ -38,17 +38,17 @@
   '((a . 1) (x . 42) (b . 2) (c . 3))
   (alist-cons-before 'b 'x 42 '((a . 1) (b . 2) (c . 3))))
 
-(test-equal "alist-cons-before, reference not found"
-  '((a . 1) (b . 2) (c . 3) (x . 42))
-  (alist-cons-before 'z 'x 42 '((a . 1) (b . 2) (c . 3))))
+(test-assert "alist-cons-before, reference not found"
+  (not (false-if-exception
+        (alist-cons-before 'z 'x 42 '((a . 1) (b . 2) (c . 3))))))
 
 (test-equal "alist-cons-after"
   '((a . 1) (b . 2) (x . 42) (c . 3))
   (alist-cons-after 'b 'x 42 '((a . 1) (b . 2) (c . 3))))
 
-(test-equal "alist-cons-after, reference not found"
-  '((a . 1) (b . 2) (c . 3) (x . 42))
-  (alist-cons-after 'z 'x 42 '((a . 1) (b . 2) (c . 3))))
+(test-assert "alist-cons-after, reference not found"
+  (not (false-if-exception
+        (alist-cons-after 'z 'x 42 '((a . 1) (b . 2) (c . 3))))))
 
 (test-equal "alist-replace"
   '((a . 1) (b . 77) (c . 3))
-- 
2.32.0