Re: using package-for-guile2.0 outside of guile.scm

["Ludovic Courtès" <ludo@gnu.org>]

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Hello,

Ricardo Wurmus <rekado@elephly.net> skribis:

> I tried to move most of the packages in gnu/packages/guile.scm to a new
> module gnu/packages/guile-xyz.scm.
>
> The only problem with this is that package-for-guile2.0 cannot be used
> in guile-xyz.scm.  I cannot compile the module when there’s a reference
> to package-for-guile2.0, even when the definition is in guile-xyz.scm.
> The definition of package-for-guile2.0 refers to guile-2.2, which is
> located in guile.scm.
>
> What to do?

The problem is that ‘package-with-guile-2.0’ needs to resolve
‘guile-2.0’.  So if you use it at the top-level, then (gnu packages
guile) has to be fully loaded, or you have to be in (gnu packages guile)
itself and ‘guile-2.0’ has been defined above.

I think we can get around it using this cute hack.  I’ll commit it if
that’s fine with you.

Ludo’.


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diff --git a/gnu/packages/guile.scm b/gnu/packages/guile.scm
index 1a3069c2fd..5bcb6f4dd7 100644
--- a/gnu/packages/guile.scm
+++ b/gnu/packages/guile.scm
@@ -413,7 +413,7 @@ GNU@tie{}Guile.  Use the @code{(ice-9 readline)} module and call its
 (define package-for-guile-2.0
   ;; A procedure that rewrites the dependency tree of the given package to use
   ;; GUILE-2.0 instead of GUILE-2.2.
-  (package-input-rewriting `((,guile-2.2 . ,guile-2.0))
+  (package-input-rewriting (delay `((,guile-2.2 . ,guile-2.0)))
                            (guile-variant-package-name "guile2.0")))
 
 (define-public guile-for-guile-emacs
diff --git a/guix/packages.scm b/guix/packages.scm
index f191327718..f4ce406f00 100644
--- a/guix/packages.scm
+++ b/guix/packages.scm
@@ -861,7 +861,10 @@ package to replace, and the second one is the replacement.
 Optionally, REWRITE-NAME is a one-argument procedure that takes the name of a
 package and returns its new name after rewrite."
   (define (rewrite p)
-    (match (assq-ref replacements p)
+    (match (assq-ref (if (promise? replacements)
+                         (force replacements)
+                         replacements)
+                     p)
       (#f  (package
              (inherit p)
              (name (rewrite-name (package-name p)))))