bug#56114: Guix does not have a documented general and practical procedure for lowering a single lowerable object to the /gnu/store/... string.

[Ludovic Courtès]

Hi Maxime,

Maxime Devos <maximedevos@telenet.be> skribis:

> Seems like we are missing a general & documented & simple to use
> 'lower-object-completely' (or maybe 'compile-object'?) procedure for
> this ...  And maybe also a ,build-object REPL command?

How about the attached patch?

Sample session:

--8<---------------cut here---------------start------------->8---
scheme@(guile-user)> ,use(gnu packages base)
scheme@(guile-user)> ,build coreutils
$11 = "/gnu/store/y8933036ljrz4ah9zcph09nmvdmmv5sf-coreutils-8.32-debug"
$12 = "/gnu/store/8fpk2cja3f07xls48jfnpgrzrljpqivr-coreutils-8.32"
scheme@(guile-user)> ,lower coreutils
$13 = #<derivation 
/gnu/store/nc93q3hmlzcgdn6jr7dv3j2m50ivn55f-coreutils-8.32.drv => 
/gnu/store/y8933036ljrz4ah9zcph09nmvdmmv5sf-coreutils-8.32-debug 
/gnu/store/8fpk2cja3f07xls48jfnpgrzrljpqivr-coreutils-8.32 7f0ebaf821e0>
scheme@(guile-user)> ,build (computed-file "foo" #~(begin (display 
"hi!\n")(mkdir #$output)(mkdir #$output:lib)))
$14 = "/gnu/store/axij9bkg56xv3k1z0l20gd6b0swn14sy-foo-lib"
$15 = "/gnu/store/h5s7k7m0fxk9n7q7729l3n4q7vyxnvpy-foo"
scheme@(guile-user)> ,build (computed-file "foo" #~(begin (display "Goeden 
dag!\n")(mkdir #$output)))
substitute: updating substitutes from 'https://ci.guix.gnu.org'... 100.0%
substitute: updating substitutes from 'https://bordeaux.guix.gnu.org'... 100.0%
substitute: updating substitutes from 'https://guix.bordeaux.inria.fr'... 100.0%
building /gnu/store/gplhka9g0bwv8b640zavw1z65y9zrvag-foo.drv...
$16 = "/gnu/store/ynvga6gxwj68mmk8ddj3i9sjhavkqah1-foo"
--8<---------------cut here---------------end--------------->8---

“lower” does what you would expect; “build” yields one value per output.

If that works for you, I’ll update the manual accordingly, and we can
always add more features (like build options) later on.  Thoughts?

Thanks,
Ludo’.

diff --git a/guix/monad-repl.scm b/guix/monad-repl.scm
index aefabdeebb..15c10efe01 100644
--- a/guix/monad-repl.scm
+++ b/guix/monad-repl.scm
@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2014, 2015, 2016 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2014, 2015, 2016, 2022 Ludovic Courtès <ludo@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -21,6 +21,12 @@ (define-module (guix monad-repl)
   #:use-module (guix monads)
   #:use-module (guix utils)
   #:use-module (guix packages)
+  #:use-module (guix status)
+  #:autoload   (guix gexp) (lower-object)
+  #:use-module ((guix derivations)
+                #:select (derivation?
+                          derivation->output-paths built-derivations))
+  #:use-module (ice-9 match)
   #:use-module (ice-9 pretty-print)
   #:use-module (system repl repl)
   #:use-module (system repl common)
@@ -69,16 +75,56 @@ (define (store-monad-language store)
                          #:guile-for-build guile)
                     'store-monad)))
 
+(define %build-verbosity 1)
+
+(define* (evaluate/print-with-store mvalue #:key build?)
+  "Run monadic value MVALUE in the store monad and print its value."
+  (with-store store
+    (set-build-options store
+                       #:print-build-trace #t
+                       #:print-extended-build-trace? #t
+                       #:multiplexed-build-output? #t)
+    (with-status-verbosity %build-verbosity
+      (let* ((guile  (or (%guile-for-build)
+                         (default-guile-derivation store)))
+             (values (run-with-store store
+                       (if build?
+                           (mlet %store-monad ((obj mvalue))
+                             (if (derivation? obj)
+                                 (mbegin %store-monad
+                                   (built-derivations (list obj))
+                                   (return
+                                    (match (derivation->output-paths obj)
+                                      (((_ . files) ...) files))))
+                                 (return (list obj))))
+                           (mlet %store-monad ((obj mvalue))
+                             (return (list obj))))
+                       #:guile-for-build guile)))
+        (for-each (lambda (value)
+                    (run-hook before-print-hook value)
+                    (pretty-print value))
+                  values)))))
+
 (define-meta-command ((run-in-store guix) repl (form))
   "run-in-store EXP
 Run EXP through the store monad."
-  (with-store store
-    (let* ((guile (or (%guile-for-build)
-                      (default-guile-derivation store)))
-           (value (run-with-store store (repl-eval repl form)
-                                  #:guile-for-build guile)))
-      (run-hook before-print-hook value)
-      (pretty-print value))))
+  (evaluate/print-with-store (repl-eval repl form)))
+
+(define-meta-command ((verbosity guix) repl (level))
+  "verbosity LEVEL
+Change build verbosity to LEVEL."
+  (set! %build-verbosity level))
+
+(define-meta-command ((lower guix) repl (form))
+  "lower OBJECT
+Lower OBJECT into a derivation and return it."
+  (evaluate/print-with-store (lower-object (repl-eval repl form))))
+
+(define-meta-command ((build guix) repl (form))
+  "build OBJECT
+Lower OBJECT and build it, returning its output file name(s)."
+  (evaluate/print-with-store (lower-object (repl-eval repl form))
+                             #:build? #t))
 
 (define-meta-command ((enter-store-monad guix) repl)
   "enter-store-monad