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

[zimoun]

Hi,

If the package source tarball is provided to ’--with-source’, then the
hash differs.  I would expect a fixed point.

Let investigate:

--8<---------------cut here---------------start------------->8---
$ guix build hello@2.10 
--with-source=hello=https://ftpmirror.gnu.org/gnu/hello/hello-2.10.tar.gz
/gnu/store/zfwhbbknkhxi3yqmp0qgh1l1crljgbm6-hello-2.10

$ guix build hello@2.10 
/gnu/store/a462kby1q51ndvxdv3b6p0rsixxrgx1h-hello-2.10
--8<---------------cut here---------------end--------------->8---

Where https://ftpmirror.gnu.org/gnu/hello/hello-2.10.tar.gz is an
official mirror.  I expect the same store item.

Why are they different?  It is because the derivations are different.
The first call contains the source tarball as an “input”; that’s fine.
The second call contains the source tarball as a derivation; again
that’s fine.  The corresponding first and second derivations are:

--8<---------------cut here---------------start------------->8---
Derive
([("out","/gnu/store/zfwhbbknkhxi3yqmp0qgh1l1crljgbm6-hello-2.10","","")]
 
,[("/gnu/store/101ny738l311p4fm3cas7jgnkzagjv6a-module-import-compiled.drv",["out"])

[...]

   ,("/gnu/store/z4s27gwacbw8f38andfsh21r8v330dag-xz-5.2.4.drv",["out"])]
 ,["/gnu/store/8a0wry8cvr405ha8d8bpjyzj5dzghigd-module-import",
 "/gnu/store/chariqd6k0sli3s7vcl4q3al0crirz5v-hello-2.10.tar.gz",
 "/gnu/store/rndq9g8877l29ha41dvsl3aj1z0gw0ng-hello-2.10-guile-builder"]

[...]

--8<---------------cut here---------------end--------------->8---

and

--8<---------------cut here---------------start------------->8---
Derive
([("out","/gnu/store/a462kby1q51ndvxdv3b6p0rsixxrgx1h-hello-2.10","","")]
 
,[("/gnu/store/101ny738l311p4fm3cas7jgnkzagjv6a-module-import-compiled.drv",["out"])
   
,("/gnu/store/1a7xfcqcxj0pqi4f81x1agcxa46v2bbm-hello-2.10.tar.gz.drv",["out"])

[...]

   ,("/gnu/store/z4s27gwacbw8f38andfsh21r8v330dag-xz-5.2.4.drv",["out"])]
 ,["/gnu/store/8a0wry8cvr405ha8d8bpjyzj5dzghigd-module-import",
 "/gnu/store/kql8b2hbsabcmany4m3hfm3wzdiymliy-hello-2.10-guile-builder"]

[...]

--8<---------------cut here---------------end--------------->8---

Therefore, I understand why the two store items have different hashes.
Although, it should be better that the derivations would be the same;
another story. :-)


What puzzled me are the corresponding ’guile-builder’s:

--8<---------------cut here---------------start------------->8---
  (define %build-inputs
    (quote
     (("source" . 
"/gnu/store/chariqd6k0sli3s7vcl4q3al0crirz5v-hello-2.10.tar.gz")
--8<---------------cut here---------------end--------------->8---

and

--8<---------------cut here---------------start------------->8---
  (define %build-inputs
    (quote
     (("source" . 
"/gnu/store/hbdalsf5lpf01x4dcknwx6xbn6n5km6k-hello-2.10.tar.gz")
--8<---------------cut here---------------end--------------->8---

but these 2 items have the same hash:

--8<---------------cut here---------------start------------->8---
$ guix hash /gnu/store/chariqd6k0sli3s7vcl4q3al0crirz5v-hello-2.10.tar.gz
0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i

$ guix hash /gnu/store/hbdalsf5lpf01x4dcknwx6xbn6n5km6k-hello-2.10.tar.gz
0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i
--8<---------------cut here---------------end--------------->8---

Why?  It is fixed-output so I was expecting the same thing.  And the
same as:

--8<---------------cut here---------------start------------->8---
$ guix download https://ftpmirror.gnu.org/gnu/hello/hello-2.10.tar.gz

Starting download of /tmp/guix-file.qkhxkp
>From https://ftpmirror.gnu.org/gnu/hello/hello-2.10.tar.gz...
following redirection to 
`https://mirrors.sarata.com/gnu/hello/hello-2.10.tar.gz'...
 …10.tar.gz  709KiB                                           549KiB/s 00:01 
[##################]
100.0%
/gnu/store/hbdalsf5lpf01x4dcknwx6xbn6n5km6k-hello-2.10.tar.gz
0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i
--8<---------------cut here---------------end--------------->8---

Why the store item of source tarball is it different when applying the
transformation?

Maxime provided a clue [1].

All the best,
simon

1: 
<https://yhetil.org/guix/bd48bb84243bb6b6a3a7f6e1350767d7c1015238.camel@telenet.be>