build-system: Add pyproject-build-system.

This is an experimental build system based on python-build-system
that implements PEP 517-compliant builds.

* doc/guix.texi (Build Systems): Add pyproject-build-system section.
* doc/contributing.texi (Python Modules): Mention pyproject.toml and the
PYTHON-TOOLCHAIN package, as well as differences to python-build-system.
* guix/build-system/pyproject.scm,
guix/build/pyproject-build-system.scm,
gnu/packages/aux-files/python/sanity-check-next.py,
gnu/packages/python-commencement.scm: New files.
* Makefile.am (MODULES): Register the new build systems.
* gnu/local.mk (GNU_SYSTEM_MODULES): Add python-commencement.scm.
* gnu/packages/python.scm (python-sans-pip, python-sans-pip-wrapper): New
variables.

Co-authored-by: Marius Bakke <marius@gnu.org>

2 files changed, 133 insertions, 1 deletions

diff --git a/gnu/packages/aux-files/python/sanity-check-next.py b/gnu/packages/aux-files/python/sanity-check-next.py
new file mode 100644
index 0000000000..a206b51d0a
--- /dev/null
+++ b/gnu/packages/aux-files/python/sanity-check-next.py
@@ -0,0 +1,99 @@
+# -*- coding: utf-8 -*-
+# GNU Guix --- Functional package management for GNU
+# Copyright © 2021, 2022 Lars-Dominik Braun <lars@6xq.net>
+#
+# This file is part of GNU Guix.
+#
+# GNU Guix 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.
+#
+# GNU Guix 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 GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+# This version adds a small change to accommodate missing python-setuptools.
+# TODO: Merge with sanity-check.py in the next core-updates cycle.
+
+from __future__ import print_function  # Python 2 support.
+import importlib
+import sys
+import traceback
+try:
+    import pkg_resources
+except ImportError:
+    print('Warning: Skipping, because python-setuptools are not available.')
+    sys.exit(0)
+
+try:
+    from importlib.machinery import PathFinder
+except ImportError:
+    PathFinder = None
+
+ret = 0
+
+# 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:
+        print('...checking requirements: ', end='')
+        req = str(dist.as_requirement())
+        # dist.activate() is not enough to actually check requirements, we
+        # have to .require() it.
+        pkg_resources.require(req)
+        print('OK')
+    except Exception as e:
+        print('ERROR:', req, repr(e))
+        ret = 1
+        continue
+
+    # Try to load top level modules. This should not have any side-effects.
+    try:
+        metalines = dist.get_metadata_lines('top_level.txt')
+    except (KeyError, EnvironmentError):
+        # distutils (i.e. #:use-setuptools? #f) will not install any metadata.
+        # This file is also missing for packages built using a PEP 517 builder
+        # such as poetry.
+        print('WARNING: cannot determine top-level modules')
+        continue
+    for name in metalines:
+        # Only available on Python 3.
+        if PathFinder and PathFinder.find_spec(name) is None:
+            # Ignore unavailable modules, often C modules, which were not
+            # installed at the top-level. Cannot use ModuleNotFoundError,
+            # because it is raised by failed imports too.
+            continue
+        try:
+            print('...trying to load module', name, end=': ')
+            importlib.import_module(name)
+            print('OK')
+        except Exception:
+            print('ERROR:')
+            traceback.print_exc(file=sys.stdout)
+            ret = 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', 'gui_scripts'}:
+            continue
+        for name, ep in v.items():
+            try:
+                print('...trying to load endpoint', group, name, end=': ')
+                ep.load()
+                print('OK')
+            except Exception:
+                print('ERROR:')
+                traceback.print_exc(file=sys.stdout)
+                ret = 1
+
+sys.exit(ret)
diff --git a/gnu/packages/python.scm b/gnu/packages/python.scm
index 00c3eb7774..0c164d7991 100644
--- a/gnu/packages/python.scm
+++ b/gnu/packages/python.scm
@@ -26,7 +26,7 @@
 ;;; Copyright © 2016, 2017 Nikita <nikita@n0.is>
 ;;; Copyright © 2016 Dylan Jeffers <sapientech@sapientech@openmailbox.org>
 ;;; Copyright © 2016 David Craven <david@craven.ch>
-;;; Copyright © 2016, 2017, 2018, 2019, 2020, 2021 Marius Bakke <marius@gnu.org>
+;;; Copyright © 2016-2022 Marius Bakke <marius@gnu.org>
 ;;; Copyright © 2016, 2017 Stefan Reichör <stefan@xsteve.at>
 ;;; Copyright © 2016, 2017 Alex Vong <alexvong1995@gmail.com>
 ;;; Copyright © 2016, 2017, 2018 Arun Isaac <arunisaac@systemreboot.net>
@@ -60,6 +60,7 @@
 ;;; Copyright © 2020, 2021 Greg Hogan <code@greghogan.com>
 ;;; Copyright © 2022 Philip McGrath <philip@philipmcgrath.com>
 ;;; Copyright © 2022 jgart <jgart@dismail.de>
+;;; Copyright © 2021 Lars-Dominik Braun <lars@6xq.net>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -87,6 +88,7 @@
   #:use-module (gnu packages hurd)
   #:use-module (gnu packages libffi)
   #:use-module (gnu packages pkg-config)
+  #:use-module (gnu packages python-build)
   #:use-module (gnu packages readline)
   #:use-module (gnu packages sqlite)
   #:use-module (gnu packages tcl)
@@ -674,6 +676,37 @@ and the unversioned commands available.")))
 (define-public python-wrapper (wrap-python3 python))
 (define-public python-minimal-wrapper (wrap-python3 python-minimal))
 
+;; The Python used in pyproject-build-system.
+(define-public python-sans-pip
+  (hidden-package
+   (package/inherit python
+     (arguments
+      (substitute-keyword-arguments (package-arguments python)
+        ((#:configure-flags flags #~())
+         #~(append '("--with-ensurepip=no")
+                   (delete "--with-ensurepip=install" #$flags))))))))
+
+(define-public python-sans-pip-wrapper
+  (wrap-python3 python-sans-pip))
+
+(define-public python-toolchain
+  (let ((base (package/inherit python-sans-pip-wrapper)))
+    (package
+      (inherit base)
+      (properties '())
+      (name "python-toolchain")
+      (propagated-inputs
+       (modify-inputs (package-propagated-inputs base)
+         (append python-pip
+                 python-pypa-build
+                 python-setuptools
+                 python-wheel)))
+      (synopsis "Python toolchain")
+      (description
+       "Python toolchain including Python itself, setuptools and pip.
+Use this package if you need a minimal Python toolchain instead of just
+the interpreter."))))
+
 (define-public micropython
   (package
     (name "micropython")