Fix build directory assertion for a PEP 517/518 world

news/6158.bugfix

@@ -0,0 +1 @@
+Fix a crash when using --no-cache-dir with PEP 517 distributions

news/6171.bugfix

@@ -0,0 +1 @@
+Fix a crash when using --no-cache-dir with PEP 517 distributions

src/pip/_internal/wheel.py

@@ -840,12 +840,6 @@ def build(
  newly built wheel, in preparation for installation.
  :return: True if all the wheels built correctly.
  """
- # TODO: This check fails if --no-cache-dir is set. And yet we
- # might be able to build into the ephemeral cache, surely?
- building_is_possible = self._wheel_dir or (
- autobuilding and self.wheel_cache.cache_dir
- )
- assert building_is_possible
 
  buildset = []
  format_control = self.finder.format_control
@@ -884,6 +878,13 @@ def build(
  if not buildset:
  return []
 
+ # Is any wheel build not using the ephemeral cache?
+ if any(not ephem_cache for _, ephem_cache in buildset):
+ have_directory_for_build = self._wheel_dir or (
+ autobuilding and self.wheel_cache.cache_dir
+ )
+ assert have_directory_for_build
+
  # TODO by @pradyunsg
  # Should break up this method into 2 separate methods.
 

tests/functional/test_install_wheel.py

@@ -420,3 +420,11 @@ def test_wheel_compile_syntax_error(script, data):
  result = script.pip('install', '--compile', package, '--no-index')
  assert 'yield from' not in result.stdout
  assert 'SyntaxError: ' not in result.stdout
+
+
+def test_wheel_install_with_no_cache_dir(script, tmpdir, data):
+ """Check wheel installations work, even with no cache.
+ """
+ package = data.packages.join("simple.dist-0.1-py2.py3-none-any.whl")
+ result = script.pip('install', '--no-cache-dir', '--no-index', package)
+ result.assert_installed('simpledist', editable=False)

tests/functional/test_pep517.py

@@ -109,3 +109,17 @@ def test_pep517_backend_requirements_already_satisfied(script, tmpdir, data):
  project_dir,
  )
  assert 'Installing backend dependencies:' not in result.stdout
+
+
+def test_pep517_install_with_no_cache_dir(script, tmpdir, data):
+ """Check builds with a custom backends work, even with no cache.
+ """
+ project_dir = make_project(
+ tmpdir, requires=['test_backend'],
+ backend="test_backend"
+ )
+ result = script.pip(
+ 'install', '--no-cache-dir', '--no-index', '-f', data.backends,
+ project_dir,
+ )
+ result.assert_installed('project', editable=False)