bug#50597: different fixed-output when using ’--with-source’ transformation

[Ludovic Courtès]

Hi,

zimoun <zimon.toutoune@gmail.com> skribis:

> On Sat, 18 Sep 2021 at 18:06, Ludovic Courtès <ludo@gnu.org> wrote:
>> zimoun <zimon.toutoune@gmail.com> skribis:
>>
>>> Why the store item of source tarball is it different when applying the
>>> transformation?
>>>
>>> Maxime provided a clue [1].
>>
>> Maxime is right: ‘--with-source’ passes #:recursive? #t unconditionally,
>> whereas it’s usually #f for a ‘url-fetch’ kind of URI.
>
> Thanks for confirming.  Why is it different?

Because we want ‘--with-source’ to also work with directories (see
comment in ‘package-with-source’).

>> What we could do is make it #t if and only if the URL denotes a local
>> file and that file is a directory.  I think that would achieve what you
>> want without any observable regression in practice.
>
> What I expect is that 2 (fixed-output) files with the same hash
> (0ssi1w…) lives at the same store location…
>
> $ guix hash /gnu/store/chariqd6k0sli3s7vcl4q3al0crirz5v-hello-2.10.tar.gz
> 0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i
>
> $ guix hash /gnu/store/hbdalsf5lpf01x4dcknwx6xbn6n5km6k-hello-2.10.tar.gz
> 0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i

The difference here is that one is marked as “recursive” and the other
is not.

The patch below does one I suggested earlier: passing #:recursive? #t if
and only if we know the source is a directory.

However it’s not enough to get the same derivation: we’d also need
<downloaded-file> to return a fixed-output derivation rather than a
plain store file name.  (See also <https://issues.guix.gnu.org/49696>.)

To be continued…

Ludo’.

diff --git a/guix/transformations.scm b/guix/transformations.scm
index 5ae1977cb2..e0f5579c28 100644
--- a/guix/transformations.scm
+++ b/guix/transformations.scm
@@ -46,6 +46,7 @@
   #:use-module (srfi srfi-37)
   #:use-module (ice-9 match)
   #:use-module (ice-9 vlist)
+  #:autoload   (web uri) (string->uri uri-scheme uri-path)
   #:export (options->transformation
             manifest-entry-with-transformations
 
@@ -106,15 +107,25 @@ extensions."
 (define* (package-with-source p uri #:optional version)
   "Return a package based on P but with its source taken from URI.  Extract
 the new package's version number from URI."
-  (let ((base (tarball-base-name (basename uri))))
+  (let ((base (tarball-base-name (basename uri)))
+        (file (match (string->uri uri)
+                (#f uri)
+                (uri (and (eq? 'file (uri-scheme uri))
+                          (uri-path uri))))))
     (let-values (((_ version*)
                   (hyphen-package-name->name+version base)))
       (package (inherit p)
                (version (or version version*
                             (package-version p)))
 
-               ;; Use #:recursive? #t to allow for directories.
-               (source (downloaded-file uri #t))))))
+               ;; Default to #:recursive? #f to match what 'url-fetch' does,
+               ;; but use #t when URI denotes a directory.
+               (source (let ((recursive?
+                              (and file
+                                   (match (stat file #f)
+                                     (#f #t)
+                                     (st (eq? 'directory (stat:type st)))))))
+                         (downloaded-file uri recursive?)))))))
 
 
 ;;;