Require expat >= 2.6 to prevent errors when creating venvs with older expat

The code in CPython uses XML_SetReparseDeferralEnabled when expat is >= 2.6 during the build.
However, when users upgrade Python independently on the expat package,
they may have expat 2.5 installed and see errors like:

    $ python3.1X -m venv venv
    Error: Command '['venv/bin/python3.1X', '-m', 'ensurepip', '--upgrade', '--default-pip']' returned non-zero exit status 1.

    $ venv/bin/python3.1X -m ensurepip --upgrade --default-pip
    Traceback (most recent call last):
      ...
      File "/tmp/.../pip-24.0-py3-none-any.whl/pip/_internal/commands/install.py", line 15, in <module>
        from pip._internal.cli.req_command import (
        ...<3 lines>...
        )
      File "/tmp/.../pip-24.0-py3-none-any.whl/pip/_internal/cli/req_command.py", line 21, in <module>
        from pip._internal.index.package_finder import PackageFinder
      File "/tmp/.../pip-24.0-py3-none-any.whl/pip/_internal/index/package_finder.py", line 30, in <module>
        from pip._internal.req import InstallRequirement
      File "/tmp/.../pip-24.0-py3-none-any.whl/pip/_internal/req/__init__.py", line 8, in <module>
        from .req_install import InstallRequirement
      File "/tmp/.../pip-24.0-py3-none-any.whl/pip/_internal/req/req_install.py", line 40, in <module>
        from pip._internal.operations.install.wheel import install_wheel
      File "/tmp/.../pip-24.0-py3-none-any.whl/pip/_internal/operations/install/wheel.py", line 39, in <module>
        from pip._vendor.distlib.scripts import ScriptMaker
      File "/tmp/.../pip-24.0-py3-none-any.whl/pip/_vendor/distlib/scripts.py", line 16, in <module>
        from .compat import sysconfig, detect_encoding, ZipFile
      File "/tmp/.../pip-24.0-py3-none-any.whl/pip/_vendor/distlib/compat.py", line 81, in <module>
        import xmlrpc.client as xmlrpclib
      File "/usr/lib64/python3.1X/xmlrpc/client.py", line 138, in <module>
        from xml.parsers import expat
      File "/usr/lib64/python3.1X/xml/parsers/expat.py", line 4, in <module>
        from pyexpat import *
    ImportError: /usr/lib64/python3.1X/lib-dynload/pyexpat.cpython-31X-x86_64-linux-gnu.so: undefined symbol: XML_SetReparseDeferralEnabled
    Traceback (most recent call last):
      ...
    subprocess.CalledProcessError: Command '['venv/bin/python3.1X', '-W', 'ignore::DeprecationWarning', '-c', '\nimport runpy\nimport sys\nsys.path = [\'/tmp/.../pip-24.0-py3-none-any.whl\'] + sys.path\nsys.argv[1:] = [\'install\', \'--no-cache-dir\', \'--no-index\', \'--find-links\', \'/tmp/...\', \'--upgrade\', \'pip\']\nrunpy.run_module("pip", run_name="__main__", alter_sys=True)\n']' returned non-zero exit status 1.

Thanks to Markus Falb for discovering this problem.

https://lists.fedoraproject.org/archives/list/python-devel@lists.fedoraproject.org/thread/7XHGWHBQDNFKNGSZTP44SSD6PQKZPG6C/

python3.12.spec

@@ -17,7 +17,7 @@ URL: https://www.python.org/
 #global prerel ...
 %global upstream_version %{general_version}%{?prerel}
 Version: %{general_version}%{?prerel:~%{prerel}}
-Release: 1%{?dist}
+Release: 2%{?dist}
 License: Python-2.0.1
 
 
@@ -251,7 +251,8 @@ BuildRequires: bluez-libs-devel
 BuildRequires: bzip2
 BuildRequires: bzip2-devel
 BuildRequires: desktop-file-utils
-BuildRequires: expat-devel
+# See the runtime requirement in the -libs subpackage
+BuildRequires: expat-devel >= 2.6
 
 BuildRequires: findutils
 BuildRequires: gcc-c++
@@ -562,6 +563,14 @@ Recommends: (%{pkgname}-tkinter%{?_isa} = %{version}-%{release} if tk%{?_isa})
 # The zoneinfo module needs tzdata
 Requires: tzdata
 
+# The requirement on libexpat is generated, but we need to version it.
+# When built with expat >= 2.6, but installed with older expat, we get:
+#   ImportError: /usr/lib64/python3.X/lib-dynload/pyexpat.cpython-....so:
+#   undefined symbol: XML_SetReparseDeferralEnabled
+# This breaks many things, including python -m venv.
+# Other subpackages (like -debug) also need this, but they all depend on -libs.
+Requires: expat >= 2.6
+
 %description -n %{pkgname}-libs
 This package contains runtime libraries for use by Python:
 - the majority of the Python standard library
@@ -1762,6 +1771,9 @@ CheckPython optimized
 # ======================================================
 
 %changelog
+* Thu Jul 04 2024 Tomáš Hrnčiar <thrnciar@redhat.com> - 3.12.4-2
+- Require expat >= 2.6 to prevent errors when creating venvs with older expat
+
 * Wed Jul 03 2024 Tomáš Hrnčiar <thrnciar@redhat.com> - 3.12.4-1
 - Update to 3.12.4
 Resolves: RHEL-44054