Fix for issue 5085 (--user set in config causes pip wheel to fail)

news/5085.bugfix

@@ -0,0 +1 @@
+Add a ``--no-user`` option and use it when installing build dependencies.

src/pip/_internal/commands/install.py

@@ -5,6 +5,7 @@
 import operator
 import os
 import shutil
+from optparse import SUPPRESS_HELP
 
 from pip._internal import cmdoptions
 from pip._internal.basecommand import RequirementCommand
@@ -83,6 +84,11 @@ def __init__(self, *args, **kw):
                  "platform. Typically ~/.local/, or %APPDATA%\\Python on "
                  "Windows. (See the Python documentation for site.USER_BASE "
                  "for full details.)")
+        cmd_opts.add_option(
+            '--no-user',
+            dest='use_user_site',
+            action='store_false',
+            help=SUPPRESS_HELP)
         cmd_opts.add_option(
             '--root',
             dest='root_path',

src/pip/_internal/operations/prepare.py

@@ -60,7 +60,7 @@ def _install_build_reqs(finder, prefix, build_requirements):
     ]
     args = [
         sys.executable, '-m', 'pip', 'install', '--ignore-installed',
-        '--prefix', prefix,
+        '--no-user', '--prefix', prefix,
     ] + list(urls)
 
     with open_spinner("Installing build dependencies") as spinner:

tests/data/src/withpyproject/pyproject.toml

@@ -0,0 +1,2 @@
+[build-system]
+requires = ["setuptools", "wheel"]

tests/data/src/withpyproject/setup.py

@@ -0,0 +1,2 @@
+from setuptools import setup
+setup(name='withpyproject', version='0.0.1')

tests/functional/test_wheel.py

@@ -236,3 +236,15 @@ def test_pip_wheel_with_pep518_build_reqs_no_isolation(script, data):
     assert wheel_file_path in result.files_created, result.stdout
     assert "Successfully built pep518" in result.stdout, result.stdout
     assert "Installing build dependencies" not in result.stdout, result.stdout
+
+
+def test_pip_wheel_with_user_set_in_config(script, data):
+    script.pip('install', 'wheel')
+    script.pip('download', 'setuptools', 'wheel', '-d', data.packages)
+    config_file = script.scratch_path / 'pip.conf'
+    script.environ['PIP_CONFIG_FILE'] = str(config_file)
+    config_file.write("[install]\nuser = true")
+    result = script.pip(
+        'wheel', data.src / 'withpyproject',
+    )
+    assert "Successfully built withpyproject" in result.stdout, result.stdout