guix: channels: Enable specifiying available builtin builders.

When computing channel instance derivations.

This is useful when you want to generate compatible derivations that can be
run with a daemon that potentially doesn't support builtin builders that the
daemon you're using to generate the derivations has.

I'm looking at this in particular because I want to use this in the data
service, since it provides substitutes for derivations, and since these can be
built on other machines, it's useful to control which builtin builders they
depend on.

Fixes: <https://issues.guix.gnu.org/67250>.

* build-aux/build-self.scm (build-program): Accept
 #:built-in-builders and pass along to port->connection or
open-connection as approriate.
(build): Accept and pass on #:built-in-builders.
* guix/channels.scm (build-from-source, build-channel-instance,
channel-instance-derivations, channel-instances->manifest,
channel-instances->derivation): Accept and pass on
 #:built-in-builders.

Change-Id: I315c990de66c6f7dca25a859165a5568abe385ea

2 files changed, 70 insertions, 26 deletions

diff --git a/build-aux/build-self.scm b/build-aux/build-self.scm
index 02822a2ee8..d9299b9af2 100644
--- a/build-aux/build-self.scm
+++ b/build-aux/build-self.scm
@@ -241,8 +241,12 @@ interface (FFI) of Guile.")
 
 (define* (build-program source version
                         #:optional (guile-version (effective-version))
-                        #:key (pull-version 0) (channel-metadata #f))
-  "Return a program that computes the derivation to build Guix from SOURCE."
+                        #:key (pull-version 0) (channel-metadata #f)
+                        built-in-builders)
+  "Return a program that computes the derivation to build Guix from SOURCE.
+If BUILT-IN-BUILDERS is provided, it should be a list of
+strings and this will be used instead of the builtin builders provided by the
+build daemon, from within the generated build program."
   (define select?
     ;; Select every module but (guix config) and non-Guix modules.
     ;; Also exclude (guix channels): it is autoloaded by (guix describe), but
@@ -331,11 +335,16 @@ interface (FFI) of Guile.")
                          ;; case, attempt to open a new connection.
                          (let* ((proto (string->number protocol-version))
                                 (store (if (integer? proto)
-                                           (port->connection (duplicate-port
-                                                              (current-input-port)
-                                                              "w+0")
-                                                             #:version proto)
-                                           (open-connection)))
+                                           (port->connection
+                                            (duplicate-port
+                                             (current-input-port)
+                                             "w+0")
+                                            #:version proto
+                                            #:built-in-builders
+                                            '#$built-in-builders)
+                                           (open-connection
+                                            #:built-in-builders
+                                            '#$built-in-builders)))
                                 (sock  (socket AF_UNIX SOCK_STREAM 0)))
                            ;; Connect to BUILD-OUTPUT and send it the raw
                            ;; build output.
@@ -406,7 +415,7 @@ Display a spinner when nothing happens."
                 (guile-version (if (> pull-version 0)
                                    "3.0"
                                    (effective-version)))
-
+                built-in-builders
                 #:allow-other-keys
                 #:rest rest)
   "Return a derivation that unpacks SOURCE into STORE and compiles Scheme
@@ -415,7 +424,9 @@ files."
   ;; SOURCE.
   (mlet %store-monad ((build  (build-program source version guile-version
                                              #:channel-metadata channel-metadata
-                                             #:pull-version pull-version))
+                                             #:pull-version pull-version
+                                             #:built-in-builders
+                                             built-in-builders))
                       (system (if system (return system) (current-system)))
                       (home -> (getenv "HOME"))
 
diff --git a/guix/channels.scm b/guix/channels.scm
index 0d7bc541cc..34f63eb833 100644
--- a/guix/channels.scm
+++ b/guix/channels.scm
@@ -704,11 +704,15 @@ that unconditionally resumes the continuation."
               store))))
 
 (define* (build-from-source instance
-                            #:key core verbose? (dependencies '()) system)
+                            #:key core verbose? (dependencies '()) system
+                            built-in-builders)
   "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.  By default, build for the current
-system, or SYSTEM if specified."
+system, or SYSTEM if specified.  If BUILT-IN-BUILDERS is
+provided, it should be a list of strings and this will be used instead of the
+builtin builders provided by the build daemon for store connections used
+during this process."
   (define name
     (symbol->string
      (channel-name (channel-instance-channel instance))))
@@ -750,20 +754,28 @@ system, or SYSTEM if specified."
                   #:verbose? verbose? #:version commit
                   #:system system
                   #:channel-metadata (channel-instance->sexp instance)
-                  #:pull-version %pull-version))))
+                  #:pull-version %pull-version
+                  #:built-in-builders
+                  built-in-builders))))
 
       ;; Build a set of modules that extend Guix using the standard method.
       (standard-module-derivation name source core dependencies)))
 
 (define* (build-channel-instance instance system
-                                 #:optional core (dependencies '()))
+                                 #:optional core (dependencies '())
+                                 #:key built-in-builders)
   "Return, as a monadic value, the derivation for INSTANCE, a channel
 instance, for SYSTEM.  DEPENDENCIES is a list of extensions providing Guile
-modules that INSTANCE depends on."
+modules that INSTANCE depends on.  If BUILT-IN-BUILDERS is
+provided, it should be a list of strings and this will be used instead of the
+builtin builders provided by the build daemon for store connections used
+during this process."
   (build-from-source instance
                      #:core core
                      #:dependencies dependencies
-                     #:system system))
+                     #:system system
+                     #:built-in-builders
+                     built-in-builders))
 
 (define (resolve-dependencies instances)
   "Return a procedure that, given one of the elements of INSTANCES, returns
@@ -793,9 +805,13 @@ list of instances it depends on."
   (lambda (instance)
     (vhash-foldq* cons '() instance edges)))
 
-(define* (channel-instance-derivations instances #:key system)
+(define* (channel-instance-derivations instances #:key system
+                                       built-in-builders)
   "Return the list of derivations to build INSTANCES, in the same order as
-INSTANCES.  Build for the current system by default, or SYSTEM if specified."
+INSTANCES.  Build for the current system by default, or SYSTEM if specified.
+If BUILT-IN-BUILDERS is provided, it should be a list of
+strings and this will be used instead of the builtin builders provided by the
+build daemon for store connections used during this process."
   (define core-instance
     ;; The 'guix' channel is treated specially: it's an implicit dependency of
     ;; all the other channels.
@@ -809,11 +825,15 @@ INSTANCES.  Build for the current system by default, or SYSTEM if specified."
   (define (instance->derivation instance)
     (mlet %store-monad ((system (if system (return system) (current-system))))
       (mcached (if (eq? instance core-instance)
-                   (build-channel-instance instance system)
+                   (build-channel-instance instance system
+                                           #:built-in-builders
+                                           built-in-builders)
                    (mlet %store-monad ((core (instance->derivation core-instance))
                                        (deps (mapm %store-monad instance->derivation
                                                    (edges instance))))
-                     (build-channel-instance instance system core deps)))
+                     (build-channel-instance instance system core deps
+                                             #:built-in-builders
+                                             built-in-builders)))
                instance
                system)))
 
@@ -915,10 +935,13 @@ derivation."
                     intro))))))
             '()))))
 
-(define* (channel-instances->manifest instances #:key system)
+(define* (channel-instances->manifest instances #:key system
+                                      built-in-builders)
   "Return a profile manifest with entries for all of INSTANCES, a list of
 channel instances.  By default, build for the current system, or SYSTEM if
-specified."
+specified.  If BUILT-IN-BUILDERS is provided, it should be a
+list of strings and this will be used instead of the builtin builders provided
+by the build daemon for store connections used during this process."
   (define (instance->entry instance drv)
     (let ((commit  (channel-instance-commit instance))
           (channel (channel-instance-channel instance)))
@@ -934,8 +957,11 @@ specified."
         (properties
          `((source ,(channel-instance->sexp instance)))))))
 
-  (mlet* %store-monad ((derivations (channel-instance-derivations instances
-                                                                  #:system system))
+  (mlet* %store-monad ((derivations (channel-instance-derivations
+                                     instances
+                                     #:system system
+                                     #:built-in-builders
+                                     built-in-builders))
                        (entries ->  (map instance->entry instances derivations)))
     (return (manifest entries))))
 
@@ -990,10 +1016,17 @@ be used as a profile hook."
   ;; The default channel profile hooks.
   (cons package-cache-file %default-profile-hooks))
 
-(define (channel-instances->derivation instances)
+(define* (channel-instances->derivation instances
+                                        #:key built-in-builders)
   "Return the derivation of the profile containing INSTANCES, a list of
-channel instances."
-  (mlet %store-monad ((manifest (channel-instances->manifest instances)))
+channel instances.  If BUILT-IN-BUILDERS is provided, it
+should be a list of strings and this will be used instead of the builtin
+builders provided by the build daemon for store connections used during this
+process."
+  (mlet %store-monad ((manifest (channel-instances->manifest
+                                 instances
+                                 #:built-in-builders
+                                 built-in-builders)))
     ;; Emit a profile in format version so that, if INSTANCES denotes an old
     ;; Guix, it can still read that profile, for instance for the purposes of
     ;; 'guix describe'.