channels: Record 'guix' channel metadata in (guix config).

Partially fixes <https://bugs.gnu.org/45896>.

* guix/config.scm.in (%channel-metadata): New variable.
* guix/describe.scm (channel-metadata): Use it.
(current-channels): New procedure.
(current-profile-entries): Clarify docstring.
* guix/self.scm (compiled-guix): Add #:channel-metadata and pass it to
'make-config.scm'.
(make-config.scm): Add #:channel-metadata and define '%channel-metadata'
in the generated file.
(guix-derivation): Add #:channel-metadata and pass it to 'compiled-guix'.
* guix/channels.scm (build-from-source): Replace 'name', 'source', and
'commit' parameters with 'instance'.  Pass #:channel-metadata to BUILD.
(build-channel-instance): Adjust accordingly.
* build-aux/build-self.scm (build-program): Add #:channel-metadata
and pass it to 'guix-derivation'.
(build): Add #:channel-metadata and pass it to 'build-program'.
* guix/scripts/describe.scm (display-profile-info): Add optional
'channels' parameter.  Pass it to 'display-profile-content'.
(display-profile-content): Add optional 'channels' parameter and honor
it.  Iterate on CHANNELS rather than on the manifest entries of
PROFILE.
(guix-describe): When PROFILE is #f, call 'current-channels' and pass it
to 'display-profile-info', unless it returns the empty list.

5 files changed, 108 insertions, 56 deletions

diff --git a/guix/channels.scm b/guix/channels.scm
index e7e1eb6fd0..3cc3b4c438 100644
--- a/guix/channels.scm
+++ b/guix/channels.scm
@@ -626,16 +626,23 @@ that unconditionally resumes the continuation."
       (values (run-with-store store mvalue)
               store))))
 
-(define* (build-from-source name source
-                            #:key core verbose? commit
-                            (dependencies '()))
-  "Return a derivation to build Guix from SOURCE, using the self-build script
-contained therein; use COMMIT as the version string.  When CORE is true, build
-package modules under SOURCE using CORE, an instance of Guix."
+(define* (build-from-source instance
+                            #:key core verbose? (dependencies '()))
+  "Return a derivation to build Guix from INSTANCE, using the self-build
+script contained therein.  When CORE is true, build package modules under
+SOURCE using CORE, an instance of Guix."
+  (define name
+    (symbol->string
+     (channel-name (channel-instance-channel instance))))
+  (define source
+    (channel-instance-checkout instance))
+  (define commit
+    (channel-instance-commit instance))
+
   ;; Running the self-build script makes it easier to update the build
   ;; procedure: the self-build script of the Guix-to-be-installed contains the
   ;; right dependencies, build procedure, etc., which the Guix-in-use may not
-  ;; be know.
+  ;; know.
   (define script
     (string-append source "/" %self-build-file))
 
@@ -661,7 +668,9 @@ package modules under SOURCE using CORE, an instance of Guix."
           ;; cause us to redo half of the BUILD computation several times just
           ;; to realize it gives the same result.
           (with-trivial-build-handler
-           (build source #:verbose? verbose? #:version commit
+           (build source
+                  #:verbose? verbose? #:version commit
+                  #:channel-metadata (channel-instance->sexp instance)
                   #:pull-version %pull-version))))
 
       ;; Build a set of modules that extend Guix using the standard method.
@@ -672,10 +681,7 @@ package modules under SOURCE using CORE, an instance of Guix."
   "Return, as a monadic value, the derivation for INSTANCE, a channel
 instance.  DEPENDENCIES is a list of extensions providing Guile modules that
 INSTANCE depends on."
-  (build-from-source (symbol->string
-                      (channel-name (channel-instance-channel instance)))
-                     (channel-instance-checkout instance)
-                     #:commit (channel-instance-commit instance)
+  (build-from-source instance
                      #:core core
                      #:dependencies dependencies))
 
diff --git a/guix/config.scm.in b/guix/config.scm.in
index b2901735d8..223c9eb418 100644
--- a/guix/config.scm.in
+++ b/guix/config.scm.in
@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2012, 2013, 2014, 2015, 2016, 2018, 2019 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2012, 2013, 2014, 2015, 2016, 2018, 2019, 2021 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2017 Caleb Ristvedt <caleb.ristvedt@cune.org>
 ;;;
 ;;; This file is part of GNU Guix.
@@ -23,6 +23,8 @@
             %guix-bug-report-address
             %guix-home-page-url
 
+            %channel-metadata
+
             %storedir
             %localstatedir
             %sysconfdir
@@ -56,6 +58,13 @@
 (define %guix-home-page-url
   "@PACKAGE_URL@")
 
+(define %channel-metadata
+  ;; When true, this is an sexp containing metadata for the 'guix' channel
+  ;; this file was built from.  This is used by (guix describe).
+
+  ;; TODO: Implement 'configure.ac' machinery to initialize it.
+  #f)
+
 (define %storedir
   "@storedir@")
 
diff --git a/guix/describe.scm b/guix/describe.scm
index ac89fc0d7c..6a31c707f0 100644
--- a/guix/describe.scm
+++ b/guix/describe.scm
@@ -23,12 +23,13 @@
   #:use-module ((guix utils) #:select (location-file))
   #:use-module ((guix store) #:select (%store-prefix store-path?))
   #:use-module ((guix config) #:select (%state-directory))
-  #:autoload   (guix channels) (sexp->channel)
+  #:autoload   (guix channels) (sexp->channel manifest-entry-channel)
   #:use-module (srfi srfi-1)
   #:use-module (ice-9 match)
   #:export (current-profile
             current-profile-date
             current-profile-entries
+            current-channels
             package-path-entries
 
             package-provenance
@@ -87,10 +88,19 @@ as a number of seconds since the Epoch, or #f if it could not be determined."
                            (string-append (dirname file) "/" target)))))
              (const #f)))))))
 
+(define (channel-metadata)
+  "Return the 'guix' channel metadata sexp from (guix config) if available;
+otherwise return #f."
+  ;; Older 'build-self.scm' would create a (guix config) file without the
+  ;; '%channel-metadata' variable.  Thus, properly deal with a lack of
+  ;; information.
+  (let ((module (resolve-interface '(guix config))))
+    (and=> (module-variable module '%channel-metadata) variable-ref)))
+
 (define current-profile-entries
   (mlambda ()
     "Return the list of entries in the 'guix pull' profile the calling process
-lives in, or #f if this is not applicable."
+lives in, or the empty list if this is not applicable."
     (match (current-profile)
       (#f '())
       (profile
@@ -105,6 +115,20 @@ lives in, or #f if this is not applicable."
               (string=? (manifest-entry-name entry) "guix"))
             (current-profile-entries))))
 
+(define current-channels
+  (mlambda ()
+    "Return the list of channels currently available, including the 'guix'
+channel.  Return the empty list if this information is missing."
+    (match (current-profile-entries)
+      (()
+       ;; As a fallback, if we're not running from a profile, use 'guix'
+       ;; channel metadata from (guix config).
+       (match (channel-metadata)
+         (#f '())
+         (sexp (or (and=> (sexp->channel sexp 'guix) list) '()))))
+      (entries
+       (filter-map manifest-entry-channel entries)))))
+
 (define (package-path-entries)
   "Return two values: the list of package path entries to be added to the
 package search path, and the list to be added to %LOAD-COMPILED-PATH.  These
diff --git a/guix/scripts/describe.scm b/guix/scripts/describe.scm
index e47d207ee0..cd5d3838a8 100644
--- a/guix/scripts/describe.scm
+++ b/guix/scripts/describe.scm
@@ -182,20 +182,18 @@ string is ~a.~%")
                           (current-output-port))))
     (display-package-search-path fmt)))
 
-(define (display-profile-info profile fmt)
+(define* (display-profile-info profile fmt
+                               #:optional
+                               (channels (profile-channels profile)))
   "Display information about PROFILE, a profile as created by (guix channels),
-in the format specified by FMT."
+in the format specified by FMT.  PROFILE can be #f, in which case CHANNELS is
+what matters."
   (define number
-    (generation-number profile))
-
-  (define channels
-    (profile-channels (if (zero? number)
-                          profile
-                          (generation-file-name profile number))))
+    (and profile (generation-number profile)))
 
   (match fmt
     ('human
-     (display-profile-content profile number))
+     (display-profile-content profile number channels))
     ('channels
      (pretty-print `(list ,@(map channel->code channels))))
     ('channels-sans-intro
@@ -213,33 +211,29 @@ in the format specified by FMT."
                   channels))))
   (display-package-search-path fmt))
 
-(define (display-profile-content profile number)
-  "Display the packages in PROFILE, generation NUMBER, in a human-readable
-way and displaying details about the channel's source code."
-  (display-generation profile number)
-  (for-each (lambda (entry)
-              (format #t "  ~a ~a~%"
-                      (manifest-entry-name entry)
-                      (manifest-entry-version entry))
-              (match (manifest-entry-channel entry)
-                ((? channel? channel)
-                 (format #t (G_ "    repository URL: ~a~%")
-                         (channel-url channel))
-                 (when (channel-branch channel)
-                   (format #t (G_ "    branch: ~a~%")
-                           (channel-branch channel)))
-                 (format #t (G_ "    commit: ~a~%")
-                         (if (supports-hyperlinks?)
-                             (channel-commit-hyperlink channel)
-                             (channel-commit channel))))
-                (_ #f)))
+(define* (display-profile-content profile number
+                                  #:optional
+                                  (channels (profile-channels profile)))
+  "Display CHANNELS along with PROFILE info, generation NUMBER, in a
+human-readable way and displaying details about the channel's source code.
+PROFILE and NUMBER "
+  (when (and number profile)
+    (display-generation profile number))
 
-            ;; Show most recently installed packages last.
-            (reverse
-             (manifest-entries
-              (profile-manifest (if (zero? number)
-                                    profile
-                                    (generation-file-name profile number)))))))
+  (for-each (lambda (channel)
+              (format #t "  ~a ~a~%"
+                      (channel-name channel)
+                      (string-take (channel-commit channel) 7))
+              (format #t (G_ "    repository URL: ~a~%")
+                      (channel-url channel))
+              (when (channel-branch channel)
+                (format #t (G_ "    branch: ~a~%")
+                        (channel-branch channel)))
+              (format #t (G_ "    commit: ~a~%")
+                      (if (supports-hyperlinks?)
+                          (channel-commit-hyperlink channel)
+                          (channel-commit channel))))
+            channels))
 
 (define %vcs-web-views
   ;; Hard-coded list of host names and corresponding web view URL templates.
@@ -295,6 +289,10 @@ text.  The hyperlink links to a web view of COMMIT, when available."
     (with-error-handling
       (match profile
         (#f
-         (display-checkout-info format))
+         (match (current-channels)
+           (()
+            (display-checkout-info format))
+           (channels
+            (display-profile-info #f format channels))))
         (profile
          (display-profile-info (canonicalize-profile profile) format))))))
diff --git a/guix/self.scm b/guix/self.scm
index 15c8ad4eb9..35fba1152d 100644
--- a/guix/self.scm
+++ b/guix/self.scm
@@ -793,7 +793,9 @@ itself."
     (((labels packages _ ...) ...)
      (cons package packages))))
 
-(define* (compiled-guix source #:key (version %guix-version)
+(define* (compiled-guix source #:key
+                        (version %guix-version)
+                        (channel-metadata #f)
                         (pull-version 1)
                         (name (string-append "guix-" version))
                         (guile-version (effective-version))
@@ -977,6 +979,8 @@ itself."
                                          %guix-package-name
                                          #:package-version
                                          version
+                                         #:channel-metadata
+                                         channel-metadata
                                          #:bug-report-address
                                          %guix-bug-report-address
                                          #:home-page-url
@@ -1070,6 +1074,7 @@ itself."
 (define* (make-config.scm #:key gzip xz bzip2
                           (package-name "GNU Guix")
                           (package-version "0")
+                          (channel-metadata #f)
                           (bug-report-address "bug-guix@gnu.org")
                           (home-page-url "https://guix.gnu.org"))
 
@@ -1083,6 +1088,7 @@ itself."
                                %guix-version
                                %guix-bug-report-address
                                %guix-home-page-url
+                               %channel-metadata
                                %system
                                %store-directory
                                %state-directory
@@ -1125,6 +1131,11 @@ itself."
                    (define %guix-bug-report-address #$bug-report-address)
                    (define %guix-home-page-url #$home-page-url)
 
+                   (define %channel-metadata
+                     ;; Metadata for the 'guix' channel in use.  This
+                     ;; information is used by (guix describe).
+                     '#$channel-metadata)
+
                    (define %gzip
                      #+(and gzip (file-append gzip "/bin/gzip")))
                    (define %bzip2
@@ -1249,11 +1260,14 @@ containing MODULE-FILES and possibly other files as well."
 
 (define* (guix-derivation source version
                           #:optional (guile-version (effective-version))
-                          #:key (pull-version 0))
+                          #:key (pull-version 0)
+                          channel-metadata)
   "Return, as a monadic value, the derivation to build the Guix from SOURCE
-for GUILE-VERSION.  Use VERSION as the version string.  PULL-VERSION specifies
-the version of the 'guix pull' protocol.  Return #f if this PULL-VERSION value
-is not supported."
+for GUILE-VERSION.  Use VERSION as the version string.  Use CHANNEL-METADATA
+as the channel metadata sexp to include in (guix config).
+
+PULL-VERSION specifies the version of the 'guix pull' protocol.  Return #f if
+this PULL-VERSION value is not supported."
   (define (shorten version)
     (if (and (string-every char-set:hex-digit version)
              (> (string-length version) 9))
@@ -1278,6 +1292,7 @@ is not supported."
     (set-guile-for-build guile)
     (let ((guix (compiled-guix source
                                #:version version
+                               #:channel-metadata channel-metadata
                                #:name (string-append "guix-"
                                                      (shorten version))
                                #:pull-version pull-version