channels: Factorize 'manifest-entry-channel' and channel serialization.

* guix/channels.scm (sexp->channel, manifest-entry-channel): New
procedures.
(profile-channels): Replace lambda by 'manifest-entry-channel'.
(channel-instance->sexp): New procedure.
(channel-instances->manifest)[instance->entry]: Use
'channel-instance->sexp' instead of inline code.

guix/channels.scm

@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2018, 2019, 2020 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2018, 2019, 2020, 2021 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2018 Ricardo Wurmus <rekado@elephly.net>
 ;;; Copyright © 2019 Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
 ;;;
@@ -802,24 +802,12 @@ derivation."
                           (derivation-input-derivation input))))
              (derivation-inputs drv))))
 
-(define (channel-instances->manifest instances)
+(define (channel-instance->sexp instance)
-  "Return a profile manifest with entries for all of INSTANCES, a list of
+  "Return an sexp representation of INSTANCE, a channel instance."
-channel instances."
-  (define (instance->entry instance drv)
   (let* ((commit  (channel-instance-commit instance))
          (channel (channel-instance-channel instance))
          (intro   (channel-introduction channel)))
-      (manifest-entry
+    `(repository
-        (name (symbol->string (channel-name channel)))
-        (version (string-take commit 7))
-        (item (if (guix-channel? channel)
-                  (if (old-style-guix? drv)
-                      (whole-package-for-legacy (string-append name "-" version)
-                                                drv)
-                      drv)
-                  drv))
-        (properties
-         `((source (repository
       (version 0)
       (url ,(channel-url channel))
       (branch ,(channel-branch channel))
@@ -835,7 +823,25 @@ channel instances."
                  ,(openpgp-format-fingerprint
                    (channel-introduction-first-commit-signer
                     intro))))))
-                          '()))))))))
+            '()))))
+
+(define (channel-instances->manifest instances)
+  "Return a profile manifest with entries for all of INSTANCES, a list of
+channel instances."
+  (define (instance->entry instance drv)
+    (let ((commit  (channel-instance-commit instance))
+          (channel (channel-instance-channel instance)))
+      (manifest-entry
+        (name (symbol->string (channel-name channel)))
+        (version (string-take commit 7))
+        (item (if (guix-channel? channel)
+                  (if (old-style-guix? drv)
+                      (whole-package-for-legacy (string-append name "-" version)
+                                                drv)
+                      drv)
+                  drv))
+        (properties
+         `((source ,(channel-instance->sexp instance)))))))
 
   (mlet* %store-monad ((derivations (channel-instance-derivations instances))
                        (entries ->  (map instance->entry instances derivations)))
@@ -900,18 +906,17 @@ to 'latest-channel-instances'."
                                                   validate-pull)))
     (channel-instances->derivation instances)))
 
-(define (profile-channels profile)
+(define* (sexp->channel sexp #:optional (name 'channel))
-  "Return the list of channels corresponding to entries in PROFILE.  If
+  "Read SEXP, a provenance sexp as created by 'channel-instance->sexp',
-PROFILE is not a profile created by 'guix pull', return the empty list."
+and return a channel called NAME.  Return #f if the sexp does not have the
-  (filter-map (lambda (entry)
+expected structure."
-                (match (assq 'source (manifest-entry-properties entry))
+  (match sexp
-                  (('source ('repository ('version 0)
+    (('repository ('version 0)
                   ('url url)
                   ('branch branch)
                   ('commit commit)
-                                         rest ...))
+                  rest ...)
-                   (channel (name (string->symbol
+     (channel (name name)
-                                   (manifest-entry-name entry)))
               (url url)
               (commit commit)
               (introduction
@@ -920,11 +925,26 @@ PROFILE is not a profile created by 'guix pull', return the empty list."
                  (('introduction intro)
                   (sexp->channel-introduction intro))))))
 
+    (_ #f)))
+
+(define (manifest-entry-channel entry)
+  "Return the channel ENTRY corresponds to, or #f if that information is
+missing or unreadable.  ENTRY must be an entry created by
+'channel-instances->manifest', with the 'source' property."
+  (let ((name (string->symbol (manifest-entry-name entry))))
+    (match (assq-ref (manifest-entry-properties entry) 'source)
+      ((sexp)
+       (sexp->channel sexp name))
+      (_
        ;; No channel information for this manifest entry.
        ;; XXX: Pre-0.15.0 Guix did not provide that information,
        ;; but there's not much we can do in that case.
-                  (_ #f)))
+       #f))))
 
+(define (profile-channels profile)
+  "Return the list of channels corresponding to entries in PROFILE.  If
+PROFILE is not a profile created by 'guix pull', return the empty list."
+  (filter-map manifest-entry-channel
               ;; Show most recently installed packages last.
               (reverse
                (manifest-entries (profile-manifest profile)))))