Allow to import pip10's main from pip9's /usr/bin/pip

Users are upgrading pip9 to pip10 by various manners,
one of them is `pip install --user --upgrade pip`.

If they do that and they run `pip` or  `pip3`, the one from /usr/bin is used.
However that's the one from this RPM package (pip9) and the import in there
fails (it tries to import from ~/.local, but pip10 is there with a bit
different API).

We add a patch as a dirty workaround to make /usr/bin/pip* work with
both pip9 (from this RPM) and pip10 (from whatever).

A proper fix is to put ~/.local/bin in front of /usr/bin in the PATH,
however others are against that and we cannot change it for existing
installs/user homes anyway.

This is a workaround for:
 * https://bugzilla.redhat.com/show_bug.cgi?id=1569488
 * https://bugzilla.redhat.com/show_bug.cgi?id=1571650

Patch is applied in %install, because /usr/bin/pip* are entrypoints.

pip9-allow-pip10-import.patch

@@ -0,0 +1,16 @@
+--- /usr/bin/pip3	2018-03-29 15:22:13.000000000 +0200
++++ pip3	2018-05-04 11:49:08.098821010 +0200
+@@ -4,7 +4,12 @@
+ import re
+ import sys
+ 
+-from pip import main
++try:
++    from pip import main
++except ImportError:
++    # user has most probably upgraded pip in their home
++    # so let them run it anyway until ~/.local/bin makes it in front of the PATH
++    from pip._internal import main
+ 
+ if __name__ == '__main__':
+     sys.argv[0] = re.sub(r'(-script\.pyw?|\.exe)?$', '', sys.argv[0])

python-pip.spec

@@ -30,7 +30,7 @@
 Name:           python-%{srcname}
 # When updating, update the bundled libraries versions bellow!
 Version:        9.0.3
-Release:        1%{?dist}
+Release:        2%{?dist}
 Summary:        A tool for installing and managing Python packages
 
 Group:          Development/Libraries
@@ -61,6 +61,24 @@ Patch0:         allow-stripping-given-prefix-from-wheel-RECORD-files.patch
 # Issue upstream: https://github.com/pypa/pip/issues/4288
 Patch1:         emit-a-warning-when-running-with-root-privileges.patch
 
+# Downstream only patch
+# Users are upgrading pip9 to pip10 by various manners,
+# one of them is `pip install --user --upgrade pip`.
+# If they do that and they run `pip` or  `pip3`, the one from /usr/bin is used.
+# However that's the one from this RPM package (pip9) and the import in there
+# fails (it tries to import from ~/.local, but pip10 is there with a bit
+# different API).
+# We add this patch as a dirty workaround to make /usr/bin/pip* work with
+# both pip9 (from this RPM) and pip10 (from whatever).
+# A proper fix is to put ~/.local/bin in front of /usr/bin in the PATH,
+# however others are against that and we cannot change it for existing
+# installs/user homes anyway.
+# https://bugzilla.redhat.com/show_bug.cgi?id=1569488
+# https://bugzilla.redhat.com/show_bug.cgi?id=1571650
+# WARNING: /usr/bin/pip* are entrypoints, this cannot be applied in %%prep!
+# %%patch10 doesn't work outside of %%prep, so we add it as a source
+Source10:        pip9-allow-pip10-import.patch
+
 %description
 pip is a package management system used to install and manage software packages
 written in Python. Many packages can be found in the Python Package Index
@@ -270,6 +288,11 @@ install -pm0644 docs/_build/man/*.1 %{buildroot}%{_mandir}/man1/pip3.1
 %endif
 %endif # with python2
 
+# before we ln -s anything, we apply Source10 patch to all pips:
+for PIP in %{buildroot}%{_bindir}/pip*; do
+  patch -p1 $PIP < %{SOURCE10}
+done
+
 mkdir -p %{buildroot}%{bashcompdir}
 %if %{with python2}
 PYTHONPATH=%{buildroot}%{python2_sitelib} \
@@ -385,6 +408,11 @@ py.test-%{python3_version} -m 'not network'
 %endif # with python3
 
 %changelog
+* Fri May 04 2018 Miro Hrončok <mhroncok@redhat.com> - 9.0.3-2
+- Allow to import pip10's main from pip9's /usr/bin/pip
+Resolves: rhbz#1569488
+Resolves: rhbz#1571650
+
 * Thu Mar 29 2018 Charalampos Stratakis <cstratak@redhat.com> - 9.0.3-1
 - Update to 9.0.3