[bug#29856] [PATCH core-updates] guix: python-build-system: Modify ".py" files in-place.

[Danny Milosavljevic <dannym@scratchpost.org>]

* guix/build/python-build-system.scm (wrap-python-program): New variable.
(wrap-program*): New variable.
(wrap): Use wrap-program*.
---
 guix/build/python-build-system.scm | 29 ++++++++++++++++++++++++++++-
 1 file changed, 28 insertions(+), 1 deletion(-)

diff --git a/guix/build/python-build-system.scm b/guix/build/python-build-system.scm
index dd07986b9..f5f6b07f8 100644
--- a/guix/build/python-build-system.scm
+++ b/guix/build/python-build-system.scm
@@ -25,6 +25,7 @@
   #:use-module (guix build utils)
   #:use-module (ice-9 match)
   #:use-module (ice-9 ftw)
+  #:use-module (ice-9 rdelim)
   #:use-module (srfi srfi-1)
   #:use-module (srfi srfi-26)
   #:export (%standard-phases
@@ -184,6 +185,32 @@ when running checks after installing the package."
                          configure-flags)))
     (call-setuppy "install" params use-setuptools?)))
 
+(define (wrap-python-program file-name vars)
+  "Wrap the given program as a Python script (in-place)"
+  (match vars
+    (("PYTHONPATH" 'prefix python-path)
+     (let ((pythonish-path (string-join python-path "', '")))
+       (with-atomic-file-replacement file-name
+         (lambda (in out)
+           (display (format #f "#!~a
+import sys
+sys.path = ['~a'] + sys.path
+" (which "python") pythonish-path) out)
+           (let loop ((line (read-line in 'concat)))
+             (if (eof-object? line)
+               #t
+               (begin
+                 (display line out)
+                 (loop (read-line in 'concat)))))))))))
+
+(define (wrap-program* file-name vars)
+  "Wrap the given program.
+   If FILE-NAME is ending in '.py', wraps it in a Python way.
+   Otherwise wraps it in a Bash way."
+  (if (string-suffix? ".py" file-name)
+    (wrap-python-program file-name vars)
+    (wrap-program file-name vars)))
+
 (define* (wrap #:key inputs outputs #:allow-other-keys)
   (define (list-of-files dir)
     (map (cut string-append dir "/" <>)
@@ -209,7 +236,7 @@ when running checks after installing the package."
                         (or (getenv "PYTHONPATH") ""))))))
     (for-each (lambda (dir)
                 (let ((files (list-of-files dir)))
-                  (for-each (cut wrap-program <> var)
+                  (for-each (cut wrap-program* <> var)
                             files)))
               bindirs)))