profiles: Add 'manifest-add'.

* guix/profiles.scm (manifest-add): New procedure.
* tests/profiles.scm (guile-1.8.8): New variable.
  ("manifest-add"): New test.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

guix/profiles.scm

@@ -47,6 +47,7 @@ (define-module (guix profiles)
             manifest-pattern?
 
             manifest-remove
+            manifest-add
             manifest-installed?
             manifest-matching-entries
 
@@ -196,6 +197,25 @@ (define (remove-entry pattern lst)
                        (manifest-entries manifest)
                        patterns)))
 
+(define (manifest-add manifest entries)
+  "Add a list of manifest ENTRIES to MANIFEST and return new manifest.
+Remove MANIFEST entries that have the same name and output as ENTRIES."
+  (define (same-entry? entry name output)
+    (match entry
+      (($ <manifest-entry> entry-name _ entry-output _ ...)
+       (and (equal? name entry-name)
+            (equal? output entry-output)))))
+
+  (make-manifest
+   (append entries
+           (fold (lambda (entry result)
+                   (match entry
+                     (($ <manifest-entry> name _ out _ ...)
+                      (filter (negate (cut same-entry? <> name out))
+                              result))))
+                 (manifest-entries manifest)
+                 entries))))
+
 (define (manifest-installed? manifest pattern)
   "Return #t if MANIFEST has an entry matching PATTERN (a manifest-pattern),
 #f otherwise."

tests/profiles.scm

@@ -40,6 +40,13 @@ (define guile-for-build
 
 ;; Example manifest entries.
 
+(define guile-1.8.8
+  (manifest-entry
+    (name "guile")
+    (version "1.8.8")
+    (item "/gnu/store/...")
+    (output "out")))
+
 (define guile-2.0.9
   (manifest-entry
     (name "guile")
@@ -101,6 +108,20 @@ (define guile-2.0.9:debug
             (null? (manifest-entries m3))
             (null? (manifest-entries m4)))))))
 
+(test-assert "manifest-add"
+  (let* ((m0 (manifest '()))
+         (m1 (manifest-add m0 (list guile-1.8.8)))
+         (m2 (manifest-add m1 (list guile-2.0.9)))
+         (m3 (manifest-add m2 (list guile-2.0.9:debug)))
+         (m4 (manifest-add m3 (list guile-2.0.9:debug))))
+    (and (match (manifest-entries m1)
+           ((($ <manifest-entry> "guile" "1.8.8" "out")) #t)
+           (_ #f))
+         (match (manifest-entries m2)
+           ((($ <manifest-entry> "guile" "2.0.9" "out")) #t)
+           (_ #f))
+         (equal? m3 m4))))
+
 (test-assert "profile-derivation"
   (run-with-store %store
     (mlet* %store-monad