Early detection of build backend with build_editable support

src/pip/_internal/distributions/sdist.py

@@ -41,7 +41,11 @@ def _setup_isolation(self, finder: PackageFinder) -> None:
  # Install any extra build dependencies that the backend requests.
  # This must be done in a second pass, as the pyproject.toml
  # dependencies must be installed before we can call the backend.
- if self.req.editable and self.req.permit_editable_wheels:
+ if (
+ self.req.editable
+ and self.req.permit_editable_wheels
+ and self.req.supports_pyproject_editable()
+ ):
  build_reqs = self._get_build_requires_editable()
  else:
  build_reqs = self._get_build_requires_wheel()

src/pip/_internal/req/req_install.py

@@ -1,6 +1,7 @@
 # The following comment should be removed at some point in the future.
 # mypy: strict-optional=False
 
+import functools
 import logging
 import os
 import shutil
@@ -53,6 +54,7 @@
  redact_auth_from_url,
 )
 from pip._internal.utils.packaging import get_metadata
+from pip._internal.utils.subprocess import runner_with_spinner_message
 from pip._internal.utils.temp_dir import TempDirectory, tempdir_kinds
 from pip._internal.utils.virtualenv import running_under_virtualenv
 from pip._internal.vcs import vcs
@@ -196,11 +198,6 @@ def __init__(
  # but after loading this flag should be treated as read only.
  self.use_pep517 = use_pep517
 
- # supports_pyproject_editable will be set to True or False when we try
- # to prepare editable metadata or build an editable wheel. None means
- # "we don't know yet".
- self.supports_pyproject_editable: Optional[bool] = None
-
  # This requirement needs more preparation before it can be built
  self.needs_more_preparation = False
 
@@ -247,6 +244,18 @@ def name(self) -> Optional[str]:
  return None
  return pkg_resources.safe_name(self.req.name)
 
+ @functools.lru_cache() # use cached_property in python 3.8+
+ def supports_pyproject_editable(self) -> bool:
+ if not self.use_pep517:
+ return False
+ assert self.pep517_backend
+ with self.build_env:
+ runner = runner_with_spinner_message(
+ "Checking if build backend supports build_editable"
+ )
+ with self.pep517_backend.subprocess_runner(runner):
+ return self.pep517_backend._supports_build_editable()
+
  @property
  def specifier(self) -> SpecifierSet:
  return self.req.specifier
@@ -505,39 +514,12 @@ def load_pyproject_toml(self) -> None:
 
  def _generate_editable_metadata(self) -> str:
  """Invokes metadata generator functions, with the required arguments."""
- if self.use_pep517:
- assert self.pep517_backend is not None
- try:
- metadata_directory = generate_editable_metadata(
- build_env=self.build_env,
- backend=self.pep517_backend,
- )
- except HookMissing as e:
- self.supports_pyproject_editable = False
- if not os.path.exists(self.setup_py_path) and not os.path.exists(
- self.setup_cfg_path
- ):
- raise InstallationError(
- f"Project {self} has a 'pyproject.toml' and its build "
- f"backend is missing the {e} hook. Since it does not "
- f"have a 'setup.py' nor a 'setup.cfg', "
- f"it cannot be installed in editable mode. "
- f"Consider using a build backend that supports PEP 660."
- )
- # At this point we have determined that the build_editable hook
- # is missing, and there is a setup.py or setup.cfg
- # so we fallback to the legacy metadata generation
- logger.info(
- "Build backend does not support editables, "
- "falling back to regular metadata preparation."
- )
- else:
- self.supports_pyproject_editable = True
- return metadata_directory
-
- # PEP 660 not supported, fall back to regular metadata preparation,
- # either using PEP 517 if supported or setup.py egg_info.
- return self._generate_metadata()
+ assert self.use_pep517
+ assert self.pep517_backend is not None
+ return generate_editable_metadata(
+ build_env=self.build_env,
+ backend=self.pep517_backend,
+ )
 
  def _generate_metadata(self) -> str:
  """Invokes metadata generator functions, with the required arguments."""
@@ -574,7 +556,11 @@ def prepare_metadata(self) -> None:
  """
  assert self.source_dir
 
- if self.editable and self.permit_editable_wheels:
+ if (
+ self.editable
+ and self.permit_editable_wheels
+ and self.supports_pyproject_editable()
+ ):
  self.metadata_directory = self._generate_editable_metadata()
  else:
  self.metadata_directory = self._generate_metadata()

src/pip/_internal/wheel_builder.py

@@ -71,7 +71,7 @@ def _should_build(
  return False
 
  if req.editable:
- if req.use_pep517 and req.supports_pyproject_editable is not False:
+ if req.supports_pyproject_editable():
  return True
  # we don't build legacy editable requirements
  return False

src/pip/_vendor/pep517/in_process/_in_process.py

@@ -103,6 +103,11 @@ def _build_backend():
  return obj
 
 
+def _supports_build_editable():
+ backend = _build_backend()
+ return hasattr(backend, "build_editable")
+
+
 def get_requires_for_build_wheel(config_settings):
  """Invoke the optional get_requires_for_build_wheel hook
 
@@ -312,6 +317,7 @@ def build_sdist(sdist_directory, config_settings):
  'build_editable',
  'get_requires_for_build_sdist',
  'build_sdist',
+ '_supports_build_editable',
 }
 
 

src/pip/_vendor/pep517/wrappers.py

@@ -154,6 +154,9 @@ def subprocess_runner(self, runner):
  finally:
  self._subprocess_runner = prev
 
+ def _supports_build_editable(self):
+ return self._call_hook('_supports_build_editable', {})
+
  def get_requires_for_build_wheel(self, config_settings=None):
  """Identify packages required for building a wheel
 

tests/unit/test_wheel_builder.py

@@ -39,7 +39,7 @@ def __init__(
  constraint: bool = False,
  source_dir: Optional[str] = "/tmp/pip-install-123/pendulum",
  use_pep517: bool = True,
- supports_pyproject_editable: Optional[bool] = None,
+ supports_pyproject_editable: bool = False,
  ) -> None:
  self.name = name
  self.is_wheel = is_wheel
@@ -48,7 +48,10 @@ def __init__(
  self.constraint = constraint
  self.source_dir = source_dir
  self.use_pep517 = use_pep517
- self.supports_pyproject_editable = supports_pyproject_editable
+ self._supports_pyproject_editable = supports_pyproject_editable
+
+ def supports_pyproject_editable(self) -> bool:
+ return self._supports_pyproject_editable
 
 
 @pytest.mark.parametrize(
@@ -66,7 +69,6 @@ def __init__(
  # We don't build reqs that are already wheels.
  (ReqMock(is_wheel=True), False, False),
  (ReqMock(editable=True, use_pep517=False), False, False),
- (ReqMock(editable=True, use_pep517=True), False, True),
  (
  ReqMock(editable=True, use_pep517=True, supports_pyproject_editable=True),
  False,