>From 919fd78b1aff6c277baca396ef962a5dcd4e23ae Mon Sep 17 00:00:00 2001
From: Lars-Dominik Braun <lars@6xq.net>
Date: Sun, 3 Jan 2021 10:30:29 +0100
Subject: [PATCH] [WIP] build-system/python: Validate installed package

* guix/build/python-build-system.scm (validate-loadable): New phase.
(%standard-phases): Use it.
---
 guix/build/python-build-system.scm | 51 ++++++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)

diff --git a/guix/build/python-build-system.scm b/guix/build/python-build-system.scm
index 09bd8465c8..edb772a7a4 100644
--- a/guix/build/python-build-system.scm
+++ b/guix/build/python-build-system.scm
@@ -148,6 +148,56 @@
       (format #t "test suite not run~%"))
   #t)
 
+(define* (validate-loadable #:key tests? inputs outputs #:allow-other-keys)
+  "Ensure packages depending on this package via setuptools work properly,
+their advertised endpoints work and their top level modules are importable
+without errors."
+  (let ((script (string-join
+'(
+;; Python 2 support.
+"from __future__ import print_function"
+"import pkg_resources, sys, importlib"
+;; Only check site-packages installed by this package, but not dependencies
+;; (which pkg_resources.working_set would include). Path supplied via argv.
+"ws = pkg_resources.find_distributions (sys.argv[1])"
+"for dist in ws:"
+"    print ('validating', repr (dist.project_name), dist.location)"
+"    try:"
+"        req = str (dist.as_requirement ())"
+;; dist.activate() is not enough to actually check requirements, we have to
+;; .require() it.
+"        pkg_resources.require (req)"
+"    except Exception as e:"
+"        print (req, e)"
+"        sys.exit (1)"
+;; Try to load entry points of console scripts too, making sure they work. They
+;; should be removed if they don’t. Other groups may not be safe, as they can
+;; depend on optional packages.
+"    for group, v in dist.get_entry_map ().items ():"
+"       if group not in {'console_scripts', }:"
+"           continue"
+"       for name, ep in v.items ():"
+"           print ('...trying to load endpoint', group, name)"
+"           ep.load ()"
+;; And finally try to load top level modules. This should not have any
+;; side-effects.
+"    for name in dist.get_metadata_lines ('top_level.txt'):"
+"        print ('...trying to load module', name)"
+"        try:"
+"            importlib.import_module (name)"
+;; Ignore non-existent modules, we only want to know if the existing ones work.
+"        except ModuleNotFoundError:"
+"            print ('......WARNING: module', name, 'not found, continuing')"
+"            continue")
+"\n")))
+    (add-installed-pythonpath inputs outputs)
+    ;; Make sure the working directory is empty (i.e. no Python modules in it)
+    (with-directory-excursion "/tmp"
+    ;; XXX: Cloak command run. Long and unreadable if it fails, provide an
+    ;; explanation instead.
+      (invoke "python" "-c" script (site-packages inputs outputs))))
+  #t)
+
 (define (python-version python)
   (let* ((version     (last (string-split python #\-)))
          (components  (string-split version #\.))
@@ -267,6 +317,7 @@ installed with setuptools."
     (replace 'install install)
     (add-after 'install 'check check)
     (add-after 'install 'wrap wrap)
+    (add-after 'check 'validate-loadable validate-loadable)
     (add-before 'strip 'rename-pth-file rename-pth-file)))
 
 (define* (python-build #:key inputs (phases %standard-phases)
-- 
2.26.2