Fallback to pep517 if setup.py is present and setuptools cannot be imported

452d7da880.patch

@@ -0,0 +1,76 @@
+From 452d7da8801ca318f280bd1c1085c60b0b6f747f Mon Sep 17 00:00:00 2001
+From: =?UTF-8?q?Tom=C3=A1=C5=A1=20Hrn=C4=8Diar?= <thrnciar@redhat.com>
+Date: Sat, 23 Apr 2022 16:56:59 +0200
+Subject: [PATCH] Fallback to pyproject.toml-based builds if setuptools cannot
+ be imported (#10717)
+
+This fallback is only triggered if the project has a `setup.py` file.
+
+Co-authored-by: Tzu-ping Chung <uranusjr@gmail.com>
+Co-authored-by: Pradyun Gedam <pradyunsg@gmail.com>
+---
+ news/10717.bugfix.rst               |  1 +
+ src/pip/_internal/cli/cmdoptions.py |  7 +++++++
+ src/pip/_internal/pyproject.py      | 11 +++++++++--
+ 3 files changed, 17 insertions(+), 2 deletions(-)
+ create mode 100644 news/10717.bugfix.rst
+
+diff --git a/news/10717.bugfix.rst b/news/10717.bugfix.rst
+new file mode 100644
+index 00000000000..950a4521763
+--- /dev/null
++++ b/news/10717.bugfix.rst
+@@ -0,0 +1 @@
++Fallback to pyproject.toml-based builds if ``setup.py`` is present in a project, but ``setuptools`` cannot be imported.
+diff --git a/src/pip/_internal/cli/cmdoptions.py b/src/pip/_internal/cli/cmdoptions.py
+index cd1e8a00f63..91b94e3028c 100644
+--- a/src/pip/_internal/cli/cmdoptions.py
++++ b/src/pip/_internal/cli/cmdoptions.py
+@@ -10,6 +10,7 @@
+ # The following comment should be removed at some point in the future.
+ # mypy: strict-optional=False
+ 
++import importlib.util
+ import logging
+ import os
+ import textwrap
+@@ -770,6 +771,12 @@ def _handle_no_use_pep517(
+         """
+         raise_option_error(parser, option=option, msg=msg)
+ 
++    # If user doesn't wish to use pep517, we check if setuptools is installed
++    # and raise error if it is not.
++    if not importlib.util.find_spec("setuptools"):
++        msg = "It is not possible to use --no-use-pep517 without setuptools installed."
++        raise_option_error(parser, option=option, msg=msg)
++
+     # Otherwise, --no-use-pep517 was passed via the command-line.
+     parser.values.use_pep517 = False
+ 
+diff --git a/src/pip/_internal/pyproject.py b/src/pip/_internal/pyproject.py
+index e183eaf8658..1e9119f3e5c 100644
+--- a/src/pip/_internal/pyproject.py
++++ b/src/pip/_internal/pyproject.py
+@@ -1,3 +1,4 @@
++import importlib.util
+ import os
+ from collections import namedtuple
+ from typing import Any, List, Optional
+@@ -89,9 +90,15 @@ def load_pyproject_toml(
+ 
+     # If we haven't worked out whether to use PEP 517 yet,
+     # and the user hasn't explicitly stated a preference,
+-    # we do so if the project has a pyproject.toml file.
++    # we do so if the project has a pyproject.toml file
++    # or if we cannot import setuptools.
++
++    # We fallback to PEP 517 when without setuptools,
++    # so setuptools can be installed as a default build backend.
++    # For more info see:
++    # https://discuss.python.org/t/pip-without-setuptools-could-the-experience-be-improved/11810/9
+     elif use_pep517 is None:
+-        use_pep517 = has_pyproject
++        use_pep517 = has_pyproject or not importlib.util.find_spec("setuptools")
+ 
+     # At this point, we know whether we're going to use PEP 517.
+     assert use_pep517 is not None

python-pip.spec

@@ -21,7 +21,7 @@
 
 Name:           python-%{srcname}
 Version:        %{base_version}%{?prerel:~%{prerel}}
-Release:        1%{?dist}
+Release:        2%{?dist}
 Summary:        A tool for installing and managing Python packages
 
 # We bundle a lot of libraries with pip, which itself is under MIT license.
@@ -89,6 +89,10 @@ Patch:         nowarn-pip._internal.main.patch
 # Upstream issue: https://github.com/pypa/packaging/issues/368
 Patch:         no-version-warning.patch
 
+# Fallback to pep517 if setup.py is present and setuptools cannot be imported
+# https://bugzilla.redhat.com/show_bug.cgi?id=2020635
+Patch:          https://github.com/pypa/pip/commit/452d7da880.patch
+
 # Downstream only patch
 # Users might have local installations of pip from using
 # `pip install --user --upgrade pip` on older/newer versions.
@@ -407,6 +411,10 @@ pytest_k='not completion and
 %{python_wheel_dir}/%{python_wheel_name}
 
 %changelog
+* Tue Apr 26 2022 Tomáš Hrnčiar <thrnciar@redhat.com> - 22.0.4-2
+- Fallback to pep517 if setup.py is present and setuptools cannot be imported
+- Fixes: rhbz#2020635
+
 * Mon Mar 21 2022 Karolina Surma <ksurma@redhat.com> - 22.0.4-1
 - Update to 22.0.4
 Resolves: rhbz#2061262