‘package-with-python2’ and ‘strip-python2-variant’

[ludo@gnu.org (Ludovic Courtès)]

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Hartmut Goebel <h.goebel@goebel-consult.de> skribis:

>> On Sun, Apr 17, 2016 at 10:54:03AM +1000, Ben Woodcroft wrote:
>>>  (define-public python2-ipython
>>> -  (let ((ipython (package-with-python2 python-ipython)))
>>> +  (let ((parent (package-with-python2
>>> +                 (strip-python2-variant python-ipython))))
>
> I wonder why this "strip-python2-variant" is not integrated into
> package-with-python2?
>
> Having it separately IMHO is of no use, it just adds additional code to
> be copy&pasted.

You’re right, we can eventually apply this patch:


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diff --git a/guix/build-system/python.scm b/guix/build-system/python.scm
index 326e6fd..3b775d6 100644
--- a/guix/build-system/python.scm
+++ b/guix/build-system/python.scm
@@ -68,7 +68,8 @@ extension, such as '.tar.gz'."
     (module-ref python 'python-2)))
 
 (define* (package-with-explicit-python python old-prefix new-prefix
-                                       #:key variant-property)
+                                       #:key
+                                       variant-property)
   "Return a procedure of one argument, P.  The procedure creates a package with
 the same fields as P, which is assumed to use PYTHON-BUILD-SYSTEM, such that
 it is compiled with PYTHON instead.  The inputs are changed recursively
@@ -130,19 +131,23 @@ pre-defined variants."
 
   transform)
 
+(define (strip-python2-variant p)
+  "Remove the 'python2-variant' property from P."
+  (package
+    (inherit p)
+    (properties (alist-delete 'python2-variant (package-properties p)))))
+
 (define package-with-python2
   ;; Note: delay call to 'default-python2' until after the 'arguments' field
   ;; of packages is accessed to avoid a circular dependency when evaluating
   ;; the top-level of (gnu packages python).
-  (package-with-explicit-python (delay (default-python2))
+  (compose (package-with-explicit-python (delay (default-python2))
                                          "python-" "python2-"
-                                #:variant-property 'python2-variant))
+                                         #:variant-property 'python2-variant)
 
-(define (strip-python2-variant p)
-  "Remove the 'python2-variant' property from P."
-  (package
-    (inherit p)
-    (properties (alist-delete 'python2-variant (package-properties p)))))
+           ;; Since this is the user-facing procedure, we always want to strip
+           ;; the 'python2-variant' property.
+           strip-python2-variant))
 
 (define* (lower name
                 #:key source inputs native-inputs outputs system target

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However, before this is possible, we must first change all patterns like:

  (define-public python-netaddr …)

  (define-public python2-netaddr
    (package-with-python2 python-netaddr))

to:

  (define-public python-netaddr
    (package
      ;; …
      (properties `((python2-variant . ,(delay python2-netaddr))))))

  (define-public python2-netaddr
    (package-with-python2 (strip-python2-variant python-netaddr)))

and make sure (with “guix build python2-netaddr -d” and similar) that
the changes have no impact on the resulting derivation.

Volunteers?  :-)

Thanks,
Ludo’.