profiles: Factor out 'manifest-lookup-package'.

* guix/profiles.scm (manifest-lookup-package): New procedure.
(gtk-icon-themes, xdg-desktop-database, xdg-mime-database): Use it.

guix/profiles.scm

@@ -445,6 +445,40 @@ replace it."
                 (cons (gexp-input thing output) deps)))
               (manifest-entries manifest)))
 
+(define (manifest-lookup-package manifest name)
+  "Return as a monadic value the first package or store path referenced by
+MANIFEST that named NAME, or #f if not found."
+  ;; Return as a monadic value the package or store path referenced by the
+  ;; manifest ENTRY, or #f if not referenced.
+  (define (entry-lookup-package entry)
+    (define (find-among-inputs inputs)
+      (find (lambda (input)
+              (and (package? input)
+                   (equal? name (package-name input))))
+            inputs))
+    (define (find-among-store-items items)
+      (find (lambda (item)
+              (equal? name (package-name->name+version
+                            (store-path-package-name item))))
+            items))
+
+    ;; TODO: Factorize.
+    (define references*
+      (store-lift references))
+
+    (with-monad %store-monad
+      (match (manifest-entry-item entry)
+        ((? package? package)
+         (match (package-transitive-inputs package)
+           (((labels inputs . _) ...)
+            (return (find-among-inputs inputs)))))
+        ((? string? item)
+         (mlet %store-monad ((refs (references* item)))
+           (return (find-among-store-items refs)))))))
+
+  (anym %store-monad
+        entry-lookup-package (manifest-entries manifest)))
+
 (define (info-dir-file manifest)
   "Return a derivation that builds the 'dir' file for all the entries of
 MANIFEST."
@@ -608,41 +642,7 @@ MANIFEST.  Single-file bundles are required by programs such as Git and Lynx."
 (define (gtk-icon-themes manifest)
   "Return a derivation that unions all icon themes from manifest entries and
 creates the GTK+ 'icon-theme.cache' file for each theme."
-  ;; Return as a monadic value the GTK+ package or store path referenced by the
+  (mlet %store-monad ((gtk+ (manifest-lookup-package manifest "gtk+")))
-  ;; manifest ENTRY, or #f if not referenced.
-  (define (entry-lookup-gtk+ entry)
-    (define (find-among-inputs inputs)
-      (find (lambda (input)
-              (and (package? input)
-                   (string=? "gtk+" (package-name input))))
-            inputs))
-
-    (define (find-among-store-items items)
-      (find (lambda (item)
-              (equal? "gtk+"
-                      (package-name->name+version
-                       (store-path-package-name item))))
-            items))
-
-    ;; TODO: Factorize.
-    (define references*
-      (store-lift references))
-
-    (with-monad %store-monad
-      (match (manifest-entry-item entry)
-        ((? package? package)
-         (match (package-transitive-inputs package)
-           (((labels inputs . _) ...)
-            (return (find-among-inputs inputs)))))
-        ((? string? item)
-         (mlet %store-monad ((refs (references* item)))
-           (return (find-among-store-items refs)))))))
-
-  (define (manifest-lookup-gtk+ manifest)
-    (anym %store-monad
-          entry-lookup-gtk+ (manifest-entries manifest)))
-
-  (mlet %store-monad ((gtk+ (manifest-lookup-gtk+ manifest)))
     (define build
       #~(begin
           (use-modules (guix build utils)
@@ -690,10 +690,9 @@ creates the GTK+ 'icon-theme.cache' file for each theme."
   "Return a derivation that builds the @file{mimeinfo.cache} database from
 desktop files.  It's used to query what applications can handle a given
 MIME type."
-  (define desktop-file-utils
+  (mlet %store-monad ((desktop-file-utils
-    (module-ref (resolve-interface '(gnu packages gnome))
+                       (manifest-lookup-package
-                'desktop-file-utils))
+                        manifest "desktop-file-utils")))
-
     (define build
       #~(begin
           (use-modules (srfi srfi-26)
@@ -712,22 +711,21 @@ MIME type."
                          #:log-port (%make-void-port "w"))
             (zero? (system* update-desktop-database destdir)))))
 
-  ;; Don't run the hook when 'desktop-file-utils' is not installed.
+    ;; Don't run the hook when 'desktop-file-utils' is not referenced.
-  (if (manifest-lookup manifest (manifest-pattern (name "desktop-file-utils")))
+    (if desktop-file-utils
         (gexp->derivation "xdg-desktop-database" build
                           #:modules '((guix build utils)
                                       (guix build union))
                           #:local-build? #t
                           #:substitutable? #f)
-      (with-monad %store-monad (return #f))))
+        (return #f))))
 
 (define (xdg-mime-database manifest)
   "Return a derivation that builds the @file{mime.cache} database from manifest
 entries.  It's used to query the MIME type of a given file."
-  (define shared-mime-info
+  (mlet %store-monad ((shared-mime-info
-    (module-ref (resolve-interface '(gnu packages gnome))
+                       (manifest-lookup-package
-                'shared-mime-info))
+                        manifest "shared-mime-info")))
-
     (define build
       #~(begin
           (use-modules (srfi srfi-26)
@@ -748,14 +746,14 @@ entries.  It's used to query the MIME type of a given file."
          (setenv "XDG_DATA_HOME" datadir)
          (zero? (system* update-mime-database destdir)))))
 
-  ;; Don't run the hook when 'shared-mime-info' is not installed.
+    ;; Don't run the hook when 'shared-mime-info' is referenced.
-  (if (manifest-lookup manifest (manifest-pattern (name "shared-mime-info")))
+    (if shared-mime-info
         (gexp->derivation "xdg-mime-database" build
                           #:modules '((guix build utils)
                                       (guix build union))
                           #:local-build? #t
                           #:substitutable? #f)
-      (with-monad %store-monad (return #f))))
+        (return #f))))
 
 (define %default-profile-hooks
   ;; This is the list of derivation-returning procedures that are called by