gnu: python-astropy: Disable downloading of iers data by default.

* gnu/packages/astronomy.scm (python-astropy): Add no download patch.
[source]: Add new patch.
* gnu/packages/patches/python-astropy-dont-download-iers-data.patch: Add file.
* gnu/local.mk (dist_patch_DATA): Register patch.

Merges: guix/guix!10344
Signed-off-by: Sharlatan Hellseher <sharlatanus@gmail.com>

3 files changed, 45 insertions, 0 deletions

diff --git a/gnu/local.mk b/gnu/local.mk
index 362f5ca500f..3b91a9eb623 100644
--- a/gnu/local.mk
+++ b/gnu/local.mk
@@ -2138,6 +2138,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/python-3.12-fix-tests.patch              \
   %D%/packages/patches/python-3.13-fix-tests.patch              \
   %D%/packages/patches/python-anyio-unuse-exceptiongroup-in-test.patch  \
+  %D%/packages/patches/python-astropy-dont-download-iers-data.patch     \
   %D%/packages/patches/python-beangulp-click-8.2-compat.patch   \
   %D%/packages/patches/python-bed-reader-use-store-samples.patch        \
   %D%/packages/patches/python-chai-drop-python2.patch           \
diff --git a/gnu/packages/astronomy.scm b/gnu/packages/astronomy.scm
index 89fa4f33988..4a7387b1910 100644
--- a/gnu/packages/astronomy.scm
+++ b/gnu/packages/astronomy.scm
@@ -3421,6 +3421,23 @@ constraints (i.e., altitude, airmass, moon separation/illumination, etc.)
        (sha256
         (base32 "1nji4flblxsq9mgiahx3r3wyfkdr5nir2iqab76r98hzp7ak3jj5"))
        (modules '((guix build utils)))
+       (patches
+        ;; Do not download updated iers data on the fly.  Refresh the
+        ;; python-astropy-iers-data package instead.
+        ;; That is, the python-astropy-iers-data package contains tables with
+        ;; an expiration date, for example with leap second information.
+        ;; The astropy.time package will try to download updated data
+        ;; once the current date is within 5 months of the expiration date.
+        ;; For reproducibility reasons it is more idiomatic to disable the
+        ;; downloading and instead regularly update python-astropy-iers-data.
+        ;; In particular some tests python-astropy and some dependent packages
+        ;; will fail 5 months 'into the future' because they will trigger this
+        ;; downloading of data.  This patch ensures that these packages can
+        ;; still be build with guix time-machine.
+        ;; E.g., this command, using a commit before this patch, will fail:
+        ;; guix time-machine --commit=86813d5779253bb50002d79ab791eeda5a8b4729
+        ;;   -- build python-astropy
+        (search-patches "python-astropy-dont-download-iers-data.patch"))
        (snippet
         '(begin
            ;; Remove Python bundles.
diff --git a/gnu/packages/patches/python-astropy-dont-download-iers-data.patch b/gnu/packages/patches/python-astropy-dont-download-iers-data.patch
new file mode 100644
index 00000000000..6c1d9626a5a
--- /dev/null
+++ b/gnu/packages/patches/python-astropy-dont-download-iers-data.patch
@@ -0,0 +1,27 @@
+commit e1e8631583ae26b1ac521afcf9b4f1fd640427fe
+Author: Hugo Buddelmeijer <hugo@buddelmeijer.nl>
+Date:   Tue Aug 4 09:33:22 2026 +0200
+
+    Set iers auto_download default to False.
+
+diff --git a/astropy/utils/iers/iers.py b/astropy/utils/iers/iers.py
+index 0541831366..acaf36826b 100644
+--- a/astropy/utils/iers/iers.py
++++ b/astropy/utils/iers/iers.py
+@@ -166,13 +166,14 @@ class Conf(_config.ConfigNamespace):
+     """
+ 
+     auto_download = _config.ConfigItem(
+-        True,
++        False,
+         "Enable auto-downloading of the latest IERS-A data.  If set to False "
+         "then the bundled IERS-A file will be used by default (even if a "
+         "newer version of the IERS-A file was previously downloaded and cached). "
+         "This parameter also controls whether internet resources will be "
+         "queried to update the leap second table if the installed version is "
+-        "out of date. Default is True.",
++        "out of date. Default is False in Guix for reproducibility.  Refresh"
++        "the python-astropy-iers-data package instead.",
+     )
+     auto_max_age = _config.ConfigItem(
+         30.0,