forge: Add with-packages.

with-packages allows for easy creation of G-expressions where a list
of specified packages are available. It is to G-expressions what `guix
shell' is to the shell. with-packages is frequently used in the
definition of CI jobs.

* forge/utils.scm: New file.

1 files changed, 65 insertions, 0 deletions

diff --git a/forge/utils.scm b/forge/utils.scm
new file mode 100644
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--- /dev/null
+++ b/forge/utils.scm
@@ -0,0 +1,65 @@
+;;; guix-forge --- Guix software forge meta-service
+;;; Copyright © 2022 Arun Isaac <arunisaac@systemreboot.net>
+;;;
+;;; This file is part of guix-forge.
+;;;
+;;; guix-forge is free software: you can redistribute it and/or modify
+;;; it under the terms of the GNU General Public License as published
+;;; by the Free Software Foundation, either version 3 of the License,
+;;; or (at your option) any later version.
+;;;
+;;; guix-forge is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+;;; General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with guix-forge.  If not, see
+;;; <https://www.gnu.org/licenses/>.
+
+(define-module (forge utils)
+  #:use-module (ice-9 match)
+  #:use-module (guix derivations)
+  #:use-module (guix gexp)
+  #:use-module (guix monads)
+  #:use-module (guix profiles)
+  #:use-module (guix search-paths)
+  #:use-module (guix store)
+  #:export (with-packages))
+
+(define (profile-with-packages packages)
+  "Return profile with PACKAGES."
+  (with-store store
+    (run-with-store store
+      (mlet* %store-monad ((prof-drv (profile-derivation
+                                      (packages->manifest packages)))
+                           (profile -> (derivation->output-path prof-drv)))
+        (mbegin %store-monad
+          (built-derivations (list prof-drv))
+          (return profile))))))
+
+(define (environment-with-packages packages)
+  "Return environment of a profile with PACKAGES. Return value is an
+association list mapping the name of an environment variable to its
+value."
+  (map (match-lambda
+         ((search-path . value)
+          (cons (search-path-specification-variable search-path)
+                value)))
+       (profile-search-paths (profile-with-packages packages))))
+
+(define (with-packages packages exp)
+  "Return a gexp executing EXP, another gexp, in an environment where
+PACKAGES are available and their search path environment variables
+have been set."
+  #~(begin
+      (use-modules (ice-9 match))
+      ;; Add a reference to the profile.
+      #$(profile-with-packages packages)
+      ;; Set the environment.
+      (for-each (match-lambda
+                  ((variable . value)
+                   (setenv variable value)))
+                '#$(environment-with-packages packages))
+      ;; Run the provided expression.
+      #$exp))