Subject: [PATCH 04/14] build-system: Add pyproject-build-system.

From: Marius Bakke <[email-masked]>
Date: Mon, 17 Oct 2022 22:11:51 +0200

From: Lars-Dominik Braun <[email-masked]>

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

* 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 <[email-masked]>
---
 Makefile.am                                   |   2 +
 gnu/local.mk                                  |   1 +
 .../aux-files/python/sanity-check-next.py     |  98 ++++
 gnu/packages/python-commencement.scm          |  64 +++
 gnu/packages/python.scm                       |  13 +
 guix/build-system/pyproject.scm               | 148 ++++++
 guix/build/pyproject-build-system.scm         | 460 ++++++++++++++++++
 7 files changed, 786 insertions(+)
 create mode 100644 gnu/packages/aux-files/python/sanity-check-next.py
 create mode 100644 gnu/packages/python-commencement.scm
 create mode 100644 guix/build-system/pyproject.scm
 create mode 100644 guix/build/pyproject-build-system.scm

diff --git a/Makefile.am b/Makefile.am
index 22dcc43f99..6ccb790c11 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -166,6 +166,7 @@ MODULES =					\
   guix/build-system/maven.scm			\
   guix/build-system/node.scm			\
   guix/build-system/perl.scm			\
+  guix/build-system/pyproject.scm		\
   guix/build-system/python.scm			\
   guix/build-system/renpy.scm			\
   guix/build-system/ocaml.scm			\
@@ -222,6 +223,7 @@ MODULES =					\
   guix/build/minetest-build-system.scm		\
   guix/build/node-build-system.scm		\
   guix/build/perl-build-system.scm		\
+  guix/build/pyproject-build-system.scm		\
   guix/build/python-build-system.scm		\
   guix/build/ocaml-build-system.scm		\
   guix/build/qt-build-system.scm		\
diff --git a/gnu/local.mk b/gnu/local.mk
index bf598cec8b..b6e0d262be 100644
--- a/gnu/local.mk
+++ b/gnu/local.mk
@@ -511,6 +511,7 @@ GNU_SYSTEM_MODULES =				\
   %D%/packages/python-build.scm			\
   %D%/packages/python-check.scm			\
   %D%/packages/python-compression.scm		\
+  %D%/packages/python-commencement.scm		\
   %D%/packages/python-crypto.scm		\
   %D%/packages/python-science.scm		\
   %D%/packages/python-web.scm			\
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..891606f72b
--- /dev/null
+++ b/gnu/packages/aux-files/python/sanity-check-next.py
@@ -0,0 +1,98 @@
+# -*- coding: utf-8 -*-
+
+# This version adds a small change to accomodate missing python-setuptools.
+# Original patch by Lars-Dominik Braun in wip-python-pep517, commit
+# 720dbe22d431262938be29dd9a9ddb78c44a99b3.
+# --- sanity-check.py	2022-06-12 14:40:06.814337702 +0200
+# +++ sanity-check.py	2022-10-16 23:21:38.990651568 +0200
+# @@ -19,9 +19,13 @@
+#  from __future__ import print_function  # Python 2 support.
+#  import importlib
+# -import pkg_resources
+#  import sys
+#  import traceback
+# +try:
+# +    import pkg_resources
+# +except ImportError:
+# +    print('Warning: Skipping, because python-setuptools are not available.')
+# +    sys.exit(0)
+
+# 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-commencement.scm b/gnu/packages/python-commencement.scm
new file mode 100644
index 0000000000..011ba2c38d
--- /dev/null
+++ b/gnu/packages/python-commencement.scm
@@ -0,0 +1,64 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2021 Lars-Dominik Braun <[email-masked]>
+;;; Copyright © 2022 Marius Bakke <[email-masked]>
+;;;
+;;; 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/>.
+
+(define-module (gnu packages python-commencement)
+  #:use-module ((guix licenses) #:prefix license:)
+  #:use-module (guix packages)
+  #:use-module (guix gexp)
+  #:use-module (guix build-system trivial)
+  #:use-module (gnu packages)
+  #:use-module (gnu packages python)
+  #:use-module (gnu packages python-build)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-26))
+
+(define-public python-toolchain
+  (package
+    (name "python-toolchain")
+    (version (package-version python))
+    (source #f)
+    (build-system trivial-build-system)
+    (arguments
+     (list #:modules '((guix build union))
+           #:builder
+           #~(begin
+               (use-modules (ice-9 match)
+                            (srfi srfi-1)
+                            (guix build union))
+               (union-build #$output
+                            (filter-map (match-lambda
+                                          ((_ . directory) directory))
+                                        %build-inputs)))))
+    (inputs
+     (list python-sans-pip-wrapper
+           python-pypa-build
+           python-pip
+           python-setuptools
+           python-wheel))
+    (native-search-paths
+     (package-native-search-paths python))
+    (search-paths
+     (package-search-paths python))
+    (license (package-license python))
+    (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.")
+    (home-page (package-home-page python))))
diff --git a/gnu/packages/python.scm b/gnu/packages/python.scm
index b54e393eb4..377fd1c282 100644
--- a/gnu/packages/python.scm
+++ b/gnu/packages/python.scm
@@ -677,6 +677,19 @@ (define* (wrap-python3 python
 (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 micropython
   (package
     (name "micropython")
diff --git a/guix/build-system/pyproject.scm b/guix/build-system/pyproject.scm
new file mode 100644
index 0000000000..8e320529cc
--- /dev/null
+++ b/guix/build-system/pyproject.scm
@@ -0,0 +1,148 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2021 Lars-Dominik Braun <[email-masked]>
+;;; Copyright © 2022 Marius Bakke <[email-masked]>
+;;;
+;;; 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/>.
+
+(define-module (guix build-system pyproject)
+  #:use-module ((gnu packages) #:select (search-auxiliary-file))
+  #:use-module (guix gexp)
+  #:use-module (guix store)
+  #:use-module (guix utils)
+  #:use-module (guix memoization)
+  #:use-module (guix gexp)
+  #:use-module (guix monads)
+  #:use-module (guix packages)
+  #:use-module (guix derivations)
+  #:use-module (guix search-paths)
+  #:use-module (guix build-system)
+  #:use-module (guix build-system gnu)
+  #:use-module (guix build-system python)
+  #:use-module (ice-9 match)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-26)
+  #:export (%pyproject-build-system-modules
+            default-python
+            pyproject-build
+            pyproject-build-system))
+
+;; Commentary:
+;;
+;; Standard build procedure for Python packages using 'pyproject.toml'.
+;; This is implemented as an extension of 'python-build-system'.
+;;
+;; Code:
+
+(define %pyproject-build-system-modules
+  ;; Build-side modules imported by default.
+  `((guix build pyproject-build-system)
+    (guix build json)
+    ,@%python-build-system-modules
+    ,@%gnu-build-system-modules))
+
+(define (default-python)
+  "Return the default Python package."
+  ;; Lazily resolve the binding to avoid a circular dependency.
+  (let ((python (resolve-interface '(gnu packages python-commencement))))
+    (module-ref python 'python-toolchain)))
+
+(define sanity-check.py
+  ;; TODO: Merge with sanity-check.py in the next rebuild cycle.
+  (search-auxiliary-file "python/sanity-check-next.py"))
+
+(define* (lower name
+                #:key source inputs native-inputs outputs system target
+                (python (default-python))
+                #:allow-other-keys
+                #:rest arguments)
+  "Return a bag for NAME."
+  (define private-keywords
+    '(#:target #:python #:inputs #:native-inputs))
+
+  (and (not target)                               ;XXX: no cross-compilation
+       (bag
+         (name name)
+         (system system)
+         (host-inputs `(,@(if source
+                              `(("source" ,source))
+                              '())
+                        ,@inputs
+
+                        ;; Keep the standard inputs of 'gnu-build-system'.
+                        ,@(standard-packages)))
+         (build-inputs `(("python" ,python)
+                         ("sanity-check.py" ,(local-file sanity-check.py))
+                         ,@native-inputs))
+         (outputs (append outputs '(wheel)))
+         (build pyproject-build)
+         (arguments (strip-keyword-arguments private-keywords arguments)))))
+
+(define* (pyproject-build name inputs
+                          #:key source
+                          (tests? #t)
+                          (configure-flags ''())
+                          (build-backend #f)
+                          (test-backend #f)
+                          (test-flags #f)
+                          (phases '%standard-phases)
+                          (outputs '("out" "wheel"))
+                          (search-paths '())
+                          (system (%current-system))
+                          (guile #f)
+                          (imported-modules %pyproject-build-system-modules)
+                          (modules '((guix build pyproject-build-system)
+                                     (guix build utils))))
+  "Build SOURCE using PYTHON, and with INPUTS."
+  (define build
+    (with-imported-modules imported-modules
+      #~(begin
+          (use-modules #$@(sexp->gexp modules))
+
+          #$(with-build-variables inputs outputs
+              #~(pyproject-build
+                 #:name #$name
+                 #:source #+source
+                 #:configure-flags #$configure-flags
+                 #:system #$system
+                 #:build-backend #$build-backend
+                 #:test-backend #$test-backend
+                 #:test-flags #$test-flags
+                 #:tests? #$tests?
+                 #:phases #$(if (pair? phases)
+                                (sexp->gexp phases)
+                                phases)
+                 #:outputs %outputs
+                 #:search-paths '#$(sexp->gexp
+                                    (map search-path-specification->sexp
+                                         search-paths))
+                 #:inputs %build-inputs)))))
+
+
+  (mlet %store-monad ((guile (package->derivation (or guile (default-guile))
+                                                  system #:graft? #f)))
+    (gexp->derivation name build
+                      #:system system
+                      #:graft? #f                 ;consistent with 'gnu-build'
+                      #:target #f
+                      #:guile-for-build guile)))
+
+(define pyproject-build-system
+  (build-system
+    (name 'pyproject)
+    (description "The PEP517-compliant Python build system")
+    (lower lower)))
+
+;;; pyproject.scm ends here
diff --git a/guix/build/pyproject-build-system.scm b/guix/build/pyproject-build-system.scm
new file mode 100644
index 0000000000..141d4d849f
--- /dev/null
+++ b/guix/build/pyproject-build-system.scm
@@ -0,0 +1,460 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2013, 2015, 2016, 2018, 2019 Ludovic Courtès <[email-masked]>
+;;; Copyright © 2013 Andreas Enge <[email-masked]>
+;;; Copyright © 2013 Nikita Karetnikov <[email-masked]>
+;;; Copyright © 2015, 2018 Mark H Weaver <[email-masked]>
+;;; Copyright © 2016 Hartmut Goebel <[email-masked]>
+;;; Copyright © 2018 Ricardo Wurmus <[email-masked]>
+;;; Copyright © 2018 Arun Isaac <[email-masked]>
+;;; Copyright © 2019, 2020, 2021 Maxim Cournoyer <[email-masked]>
+;;; Copyright © 2020 Jakub Kądziołka <[email-masked]>
+;;; Copyright © 2020 Efraim Flashner <[email-masked]>
+;;; Copyright © 2021 Maxime Devos <[email-masked]>
+;;;
+;;; The above copyright is taken from python-build-system.  Contributions
+;;; made only to this module are listed below:
+;;; Copyright © 2021 Lars-Dominik Braun <[email-masked]>
+;;; Copyright © 2022 Marius Bakke <[email-masked]>
+;;;
+;;; 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/>.
+
+(define-module (guix build pyproject-build-system)
+  #:use-module ((guix build gnu-build-system) #:prefix gnu:)
+  #:use-module (guix build utils)
+  #:use-module (guix build json)
+  #:use-module (ice-9 match)
+  #:use-module (ice-9 ftw)
+  #:use-module (ice-9 format)
+  #:use-module (ice-9 rdelim)
+  #:use-module (ice-9 regex)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-26)
+  #:use-module (srfi srfi-34)
+  #:use-module (srfi srfi-35)
+  #:export (%standard-phases
+            add-installed-pythonpath
+            site-packages
+            python-version
+            pyproject-build))
+
+;; Commentary:
+;;
+;; PEP 517-compatible build system for Python packages.
+;;
+;; PEP 517 mandates the use of a TOML file called pyproject.toml at the
+;; project root, describing build and runtime dependencies, as well as the
+;; build system, which can be different from setuptools. This module uses
+;; that file to extract the build system used and call its wheel-building
+;; entry point build_wheel (see 'build). setuptools’ wheel builder is
+;; used as a fallback if either no pyproject.toml exists or it does not
+;; declare a build-system. It supports config_settings through the
+;; standard #:configure-flags argument.
+;;
+;; This wheel, which is just a ZIP file with a file structure defined
+;; by PEP 427 (https://www.python.org/dev/peps/pep-0427/), is then unpacked
+;; and its contents are moved to the appropriate locations in 'install.
+;;
+;; Then entry points, as defined by the PyPa Entry Point Specification
+;; (https://packaging.python.org/specifications/entry-points/) are read
+;; from a file called entry_points.txt in the package’s site-packages
+;; subdirectory and scripts are written to bin/. These are not part of a
+;; wheel and expected to be created by the installing utility.
+;;
+;; Caveats:
+;; - There is no support for in-tree build backends.
+
+;; Base error type.
+(define-condition-type &python-build-error &error
+  python-build-error?)
+
+;; Raised when 'check cannot find a valid test system in the inputs.
+(define-condition-type &test-system-not-found &python-build-error
+  test-system-not-found?)
+
+;; Raised when multiple wheels are created by 'build.
+(define-condition-type &cannot-extract-multiple-wheels &python-build-error
+  cannot-extract-multiple-wheels?)
+
+;; Raised, when no wheel has been built by the build system.
+(define-condition-type &no-wheels-built &python-build-error
+  no-wheels-built?)
+
+(define* (sanity-check #: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 ((sanity-check.py (assoc-ref inputs "sanity-check.py")))
+    ;; Make sure the working directory is empty (i.e. no Python modules in it)
+    (with-directory-excursion "/tmp"
+      (invoke "python" sanity-check.py (site-packages inputs outputs)))))
+
+(define* (build #:key outputs build-backend configure-flags #:allow-other-keys)
+  "Build a given Python package."
+
+  (define (pyproject.toml->build-backend file)
+    "Look up the build backend in a pyproject.toml file."
+    (call-with-input-file file
+      (lambda (in)
+        (let loop ((line (read-line in 'concat)))
+          (if (eof-object? line)
+              #f
+              (let ((m (string-match "build-backend = [\"'](.+)[\"']" line)))
+                (if m (match:substring m 1)
+                    (loop (read-line in 'concat)))))))))
+
+  (let* ((wheel-output (assoc-ref outputs "wheel"))
+         (wheel-dir (if wheel-output wheel-output "dist"))
+         ;; There is no easy way to get data from Guile into Python via
+         ;; s-expressions, but we have JSON serialization already, which Python
+         ;; also supports out-of-the-box.
+         (config-settings (call-with-output-string (cut write-json configure-flags <>)))
+         ;; python-setuptools’ default backend supports setup.py *and*
+         ;; pyproject.toml. Allow overriding this automatic detection via
+         ;; build-backend.
+         (auto-build-backend (if (file-exists? "pyproject.toml")
+                               (pyproject.toml->build-backend "pyproject.toml")
+                               #f))
+         ;; Use build system detection here and not in importer, because a) we
+         ;; have alot of legacy packages and b) the importer cannot update arbitrary
+         ;; fields in case a package switches its build system.
+         (use-build-backend (or
+                              build-backend
+                              auto-build-backend
+                              "setuptools.build_meta")))
+    (format #t "Using '~a' to build wheels, auto-detected '~a', override '~a'.~%"
+               use-build-backend auto-build-backend build-backend)
+    (mkdir-p wheel-dir)
+    ;; Call the PEP 517 build function, which drops a .whl into wheel-dir.
+    (invoke "python" "-c" "import sys, importlib, json
+config_settings = json.loads (sys.argv[3])
+builder = importlib.import_module(sys.argv[1])
+builder.build_wheel(sys.argv[2], config_settings=config_settings)"
+            use-build-backend wheel-dir config-settings)))
+
+(define* (check #:key inputs outputs tests? test-backend test-flags #:allow-other-keys)
+  "Run the test suite of a given Python package."
+  (if tests?
+    ;; Unfortunately with PEP 517 there is no common method to specify test
+    ;; systems. Guess test system based on inputs instead.
+    (let* ((pytest (which "pytest"))
+           (nosetests (which "nosetests"))
+           (nose2 (which "nose2"))
+           (have-setup-py (file-exists? "setup.py"))
+           (use-test-backend
+            (or
+              test-backend
+              ;; Prefer pytest
+              (if pytest 'pytest #f)
+              (if nosetests 'nose #f)
+              (if nose2 'nose2 #f)
+              ;; But fall back to setup.py, which should work for most
+              ;; packages. XXX: would be nice not to depend on setup.py here? fails
+              ;; more often than not to find any tests at all. Maybe we can run
+              ;; `python -m unittest`?
+              (if have-setup-py 'setup.py #f))))
+        (format #t "Using ~a~%" use-test-backend)
+        (match use-test-backend
+          ('pytest
+           (apply invoke (cons pytest (or test-flags '("-vv")))))
+          ('nose
+           (apply invoke (cons nosetests (or test-flags '("-v")))))
+          ('nose2
+           (apply invoke (cons nose2 (or test-flags '("-v" "--pretty-assert")))))
+          ('setup.py
+           (apply invoke (append '("python" "setup.py") (or test-flags '("test" "-v")))))
+          ;; The developer should explicitly disable tests in this case.
+          (else (raise (condition (&test-system-not-found))))))
+      (format #t "test suite not run~%")))
+
+(define (python-version python)
+  (let* ((version     (last (string-split python #\-)))
+         (components  (string-split version #\.))
+         (major+minor (take components 2)))
+    (string-join major+minor ".")))
+
+(define (python-output outputs)
+  "Return the path of the python output, if there is one, or fall-back to out."
+  (or (assoc-ref outputs "python")
+      (assoc-ref outputs "out")))
+
+(define (site-packages inputs outputs)
+  "Return the path of the current output's Python site-package."
+  (let* ((out (python-output outputs))
+         (python (assoc-ref inputs "python")))
+    (string-append out "/lib/python" (python-version python) "/site-packages")))
+
+(define (add-installed-pythonpath inputs outputs)
+  "Prepend the site-package of OUTPUT to GUIX_PYTHONPATH.  This is useful when
+running checks after installing the package."
+  (setenv "GUIX_PYTHONPATH" (string-append (site-packages inputs outputs) ":"
+                                           (getenv "GUIX_PYTHONPATH"))))
+
+(define* (add-install-to-pythonpath #:key inputs outputs #:allow-other-keys)
+  "A phase that just wraps the 'add-installed-pythonpath' procedure."
+  (add-installed-pythonpath inputs outputs))
+
+(define* (add-install-to-path #:key outputs #:allow-other-keys)
+  "Adding Python scripts to PATH is also often useful in tests."
+  (setenv "PATH" (string-append (assoc-ref outputs "out")
+                                "/bin:"
+                                (getenv "PATH"))))
+
+(define* (install #:key inputs outputs (configure-flags '()) #:allow-other-keys)
+  "Install a wheel file according to PEP 427"
+  ;; See https://www.python.org/dev/peps/pep-0427/#installing-a-wheel-distribution-1-0-py32-none-any-whl
+  (let* ((site-dir (site-packages inputs outputs))
+         (python (assoc-ref inputs "python"))
+         (out (assoc-ref outputs "out")))
+    (define (extract file)
+      "Extract wheel (ZIP file) into site-packages directory"
+      ;; Use Python’s zipfile to avoid extra dependency
+      (invoke "python" "-m" "zipfile" "-e" file site-dir))
+
+    (define python-hashbang
+      (string-append "#!" python "/bin/python"))
+
+    (define* (merge-directories source destination #:optional (post-move #f))
+      "Move all files in SOURCE into DESTINATION, merging the two directories."
+      (format #t "Merging directory ~a into ~a~%" source destination)
+      (for-each
+        (lambda (file)
+          (format #t "~a/~a -> ~a/~a~%" source file destination file)
+          (mkdir-p destination)
+          (rename-file
+              (string-append source "/" file)
+              (string-append destination "/" file))
+          (when post-move
+            (post-move file)))
+        (scandir source (negate (cut member <> '("." "..")))))
+      (rmdir source))
+
+    (define (expand-data-directory directory)
+      "Move files from all .data subdirectories to their respective
+destinations."
+      ;; Python’s distutils.command.install defines this mapping from source to
+      ;; destination mapping.
+      (let ((source (string-append directory "/scripts"))
+            (destination (string-append out "/bin")))
+        (when (file-exists? source)
+          (merge-directories
+           source
+           destination
+           (lambda (f)
+             (let ((dest-path (string-append destination "/" f)))
+               (chmod dest-path #o755)
+               (substitute* dest-path (("#!python") python-hashbang)))))))
+      ;; data can create arbitrary directory structures. Most commonly
+      ;; it is used for share/.
+      (let ((source (string-append directory "/data"))
+            (destination out))
+        (when (file-exists? source)
+          (merge-directories source destination)))
+      (let* ((distribution (car (string-split (basename directory) #\-)))
+            (source (string-append directory "/headers"))
+            (destination (string-append out "/include/python" (python-version python) "/" distribution)))
+        (when (file-exists? source)
+          (merge-directories source destination))))
+
+  (define (list-directories base predicate)
+    ;; Cannot use find-files here, because it’s recursive.
+    (scandir
+      base
+      (lambda (name)
+        (let ((stat (lstat (string-append base "/" name))))
+        (and
+          (not (member name '("." "..")))
+          (eq? (stat:type stat) 'directory)
+          (predicate name stat))))))
+
+  (let* ((wheel-output (assoc-ref outputs "wheel"))
+         (wheel-dir (if wheel-output wheel-output "dist"))
+         (wheels (map (cut string-append wheel-dir "/" <>)
+                      (scandir wheel-dir (cut string-suffix? ".whl" <>)))))
+    (cond
+    ((> (length wheels) 1) ; This code does not support multiple wheels
+                                ; yet, because their outputs would have to be
+                                ; merged properly.
+      (raise (condition (&cannot-extract-multiple-wheels))))
+      ((= (length wheels) 0)
+       (raise (condition (&no-wheels-built)))))
+    (for-each extract wheels))
+  (let ((datadirs (map
+                    (cut string-append site-dir "/" <>)
+                    (list-directories site-dir (file-name-predicate "\\.data$")))))
+    (for-each (lambda (directory)
+                (expand-data-directory directory)
+                (rmdir directory))
+              datadirs))))
+
+(define* (compile-bytecode #:key inputs outputs (configure-flags '()) #:allow-other-keys)
+  "Compile installed byte-code in site-packages."
+  (let ((site-dir (site-packages inputs outputs)))
+    (invoke "python" "-m" "compileall" "--invalidation-mode=unchecked-hash"
+            site-dir)))
+
+(define* (create-entrypoints #:key inputs outputs (configure-flags '()) #:allow-other-keys)
+  "Implement Entry Points Specification
+(https://packaging.python.org/specifications/entry-points/) by PyPa,
+which creates runnable scripts in bin/ from entry point specification
+file entry_points.txt. This is necessary, because wheels do not contain
+these binaries and installers are expected to create them."
+
+  (define (entry-points.txt->entry-points file)
+    "Specialized parser for Python configfile-like files, in particular
+entry_points.txt. Returns a list of console_script and gui_scripts
+entry points."
+    (call-with-input-file file
+      (lambda (in)
+        (let loop ((line (read-line in))
+                   (inside #f)
+                   (result '()))
+          (if (eof-object? line)
+            result
+            (let* ((group-match (string-match "^\\[(.+)\\]$" line))
+                  (group-name (if group-match (match:substring group-match 1) #f))
+                  (next-inside
+                   (if (not group-name)
+                     inside
+                     (or
+                       (string=? group-name "console_scripts")
+                       (string=? group-name "gui_scripts"))))
+                  (item-match (string-match "^([^ =]+)\\s*=\\s*([^:]+):(.+)$" line)))
+              (if (and inside item-match)
+                (loop (read-line in) next-inside (cons (list
+                                                        (match:substring item-match 1)
+                                                        (match:substring item-match 2)
+                                                        (match:substring item-match 3))
+                                                         result))
+                (loop (read-line in) next-inside result))))))))
+
+  (define (create-script path name module function)
+    "Create a Python script from an entry point’s NAME, MODULE and
+  FUNCTION and return write it to PATH/NAME."
+    (let ((interpreter (which "python"))
+          (file-path (string-append path "/" name)))
+      (format #t "Creating entry point for '~a.~a' at '~a'.~%" module function
+                 file-path)
+      (call-with-output-file file-path
+        (lambda (port)
+          ;; Technically the script could also include search-paths,
+          ;; but having a generic 'wrap phases also handles manually
+          ;; written entry point scripts.
+          (format port "#!~a
+# Auto-generated entry point script.
+import sys
+import ~a as mod
+sys.exit (mod.~a ())~%" interpreter module function)))
+        (chmod file-path #o755)))
+
+  (let* ((site-dir (site-packages inputs outputs))
+         (out (assoc-ref outputs "out"))
+         (bin-dir (string-append out "/bin"))
+         (entry-point-files (find-files site-dir "^entry_points.txt$")))
+    (mkdir-p bin-dir)
+    (for-each
+      (lambda (f)
+        (for-each
+          (lambda (ep) (apply create-script (cons bin-dir ep)))
+          (entry-points.txt->entry-points f)))
+      entry-point-files)))
+
+(define* (wrap #:key inputs outputs search-paths #:allow-other-keys)
+  (define (list-of-files dir)
+    (find-files dir (lambda (file stat)
+                      (and (eq? 'regular (stat:type stat))
+                           (not (wrapped-program? file))))))
+
+  (define bindirs
+    (append-map (match-lambda
+                  ((_ . dir)
+                   (list (string-append dir "/bin")
+                         (string-append dir "/sbin"))))
+                outputs))
+
+  ;; Do not require "bash" to be present in the package inputs
+  ;; even when there is nothing to wrap.
+  ;; Also, calculate (sh) only once to prevent some I/O.
+  (define %sh (delay (search-input-file inputs "bin/bash")))
+  (define (sh) (force %sh))
+
+  (let* ((var `("GUIX_PYTHONPATH" prefix
+                ,(search-path-as-string->list
+                  (or (getenv "GUIX_PYTHONPATH") "")))))
+    (for-each (lambda (dir)
+                (let ((files (list-of-files dir)))
+                  (for-each (cut wrap-program <> #:sh (sh) var)
+                            files)))
+              bindirs)))
+
+(define* (set-SOURCE-DATE-EPOCH #:rest _)
+  "Set the 'SOURCE_DATE_EPOCH' environment variable.  This is used by tools
+that incorporate timestamps as a way to tell them to use a fixed timestamp.
+See https://reproducible-builds.org/specs/source-date-epoch/."
+  ;; Use a post-1980 timestamp because the Zip format used in wheels do
+  ;; not support timestamps before 1980.
+  (setenv "SOURCE_DATE_EPOCH" "315619200"))
+
+(define* (enable-bytecode-determinism #:rest _)
+  "Improve determinism of pyc files."
+  ;; Use deterministic hashes for strings, bytes, and datetime objects.
+  (setenv "PYTHONHASHSEED" "0")
+  ;; Prevent Python from creating .pyc files when loading modules (such as
+  ;; when running a test suite).
+  (setenv "PYTHONDONTWRITEBYTECODE" "1"))
+
+(define* (ensure-no-cythonized-files #:rest _)
+  "Check the source code for @code{.c} files which may have been pre-generated
+by Cython."
+  (for-each
+    (lambda (file)
+      (let ((generated-file
+              (string-append (string-drop-right file 3) "c")))
+        (when (file-exists? generated-file)
+          (format #t "Possible Cythonized file found: ~a~%" generated-file))))
+    (find-files "." "\\.pyx$")))
+
+(define %standard-phases
+  ;; The build phase only builds C extensions and copies the Python sources,
+  ;; while the install phase copies then byte-compiles the sources to the
+  ;; prefix directory.  The check phase is moved after the installation phase
+  ;; to ease testing the built package.
+  (modify-phases gnu:%standard-phases
+    (add-after 'unpack 'enable-bytecode-determinism
+      enable-bytecode-determinism)
+    (add-after 'enable-bytecode-determinism 'ensure-no-cythonized-files
+      ensure-no-cythonized-files)
+    (replace 'set-SOURCE-DATE-EPOCH set-SOURCE-DATE-EPOCH)
+    (delete 'bootstrap)
+    (delete 'configure)                 ;not needed
+    (replace 'build build)
+    (delete 'check)                     ;moved after the install phase
+    (replace 'install install)
+    (add-after 'install 'add-install-to-pythonpath add-install-to-pythonpath)
+    (add-after 'add-install-to-pythonpath 'add-install-to-path
+      add-install-to-path)
+    (add-after 'add-install-to-path 'wrap wrap)
+    ;; must be before tests, so they can use installed packages’ entry points.
+    (add-before 'wrap 'create-entrypoints create-entrypoints)
+    (add-after 'wrap 'check check)
+    (add-after 'check 'sanity-check sanity-check)
+    (add-before 'check 'compile-bytecode compile-bytecode)))
+
+(define* (pyproject-build #:key inputs (phases %standard-phases)
+                          #:allow-other-keys #:rest args)
+  "Build the given Python package, applying all of PHASES in order."
+  (apply gnu:gnu-build #:inputs inputs #:phases phases args))
+
+;;; pyproject-build-system.scm ends here
-- 
2.38.0