[bug#44590] [WIP PATCH CORE-UPDATES] build/python: Check for cythonized files.

[Efraim Flashner <efraim@flashner.co.il>]

* guix/build/python-build-system.scm (ensure-no-cythonized-files): New procedure.
(%standard-phases): Add it.
---

This patch only checks if a file exists and suggests it may be
cythonized. It doesn't check the first line for the string "generated by
Cython" in that file or in any file. It also doesn't error when it
thinks it finds a file. It does provide a good visual queue that the
source needs more scrutiny before being added.

---
 guix/build/python-build-system.scm | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/guix/build/python-build-system.scm b/guix/build/python-build-system.scm
index 4a07496d22..bc34e22df8 100644
--- a/guix/build/python-build-system.scm
+++ b/guix/build/python-build-system.scm
@@ -8,6 +8,7 @@
 ;;; Copyright © 2018 Arun Isaac <arunisaac@systemreboot.net>
 ;;; Copyright © 2019, 2020 Maxim Cournoyer <maxim.cournoyer@gmail.com>
 ;;; Copyright © 2020 Jakub Kądziołka <kuba@kadziolka.net>
+;;; Copyright © 2020 Efraim Flashner <efraim@flashner.co.il>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -262,6 +263,18 @@ installed with setuptools."
   (setenv "PYTHONHASHSEED" "0")
   #t)
 
+(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)
+          (warning (G_ "Possible Cythonized file found: ~a~%") generated-file))))
+    (find-files "." "\\.pyx$"))
+  #t)
+
 (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
@@ -271,6 +284,8 @@ installed with setuptools."
     (add-after 'unpack 'ensure-no-mtimes-pre-1980 ensure-no-mtimes-pre-1980)
     (add-after 'ensure-no-mtimes-pre-1980 'enable-bytecode-determinism
       enable-bytecode-determinism)
+    (add-after 'enable-bytecode-determinism 'ensure-no-cythonized-files
+      ensure-no-cythonized-files)
     (delete 'bootstrap)
     (delete 'configure)                 ;not needed
     (replace 'build build)
-- 
2.29.2