Merge pull request #5841 from benoit-pierre/fix_python_src/pip

fix support for invoking pip using `python src/pip ...`

news/5841.bugfix

@@ -0,0 +1 @@
+Fix support for invoking pip using `python src/pip ...`.

src/pip/_internal/build_env.py

@@ -10,6 +10,7 @@
 
 from pip._vendor.pkg_resources import Requirement, VersionConflict, WorkingSet
 
+from pip import __file__ as pip_location
 from pip._internal.utils.misc import call_subprocess
 from pip._internal.utils.temp_dir import TempDirectory
 from pip._internal.utils.ui import open_spinner
@@ -103,8 +104,9 @@ def missing_requirements(self, reqs):
 
  def install_requirements(self, finder, requirements, message):
  args = [
- sys.executable, '-m', 'pip', 'install', '--ignore-installed',
- '--no-user', '--prefix', self.path, '--no-warn-script-location',
+ sys.executable, os.path.dirname(pip_location), 'install',
+ '--ignore-installed', '--no-user', '--prefix', self.path,
+ '--no-warn-script-location',
  ]
  if logger.getEffectiveLevel() <= logging.DEBUG:
  args.append('-v')

tests/functional/test_install.py

@@ -37,6 +37,19 @@ def test_pep518_uses_build_env(script, data, common_wheels, command, variant):
  )
 
 
+def test_pep518_build_env_uses_same_pip(script, data, pip_src, common_wheels):
+ """Ensure the subprocess call to pip for installing the
+ build dependencies is using the same version of pip.
+ """
+ with open(script.scratch_path / 'pip.py', 'w') as fp:
+ fp.write('raise ImportError')
+ script.run(
+ 'python', pip_src / 'src/pip', 'install', '--no-index',
+ '-f', common_wheels, '-f', data.packages,
+ data.src.join("pep518-3.0"),
+ )
+
+
 def test_pep518_refuses_invalid_requires(script, data, common_wheels):
  result = script.pip(
  'install', '-f', common_wheels,