Error out if installing a pyproject.toml-style (PEP 517) project in editable mode.

Author: cjerdonek

news/6314.feature

@@ -0,0 +1,2 @@
+Error out with an informative message if one tries to install a
+``pyproject.toml``-style (PEP 517) source tree using ``--editable`` mode.

src/pip/_internal/pyproject.py

@@ -49,11 +49,27 @@ def read_pyproject_toml(path):
     return build_system
 
 
+def make_editable_error(req_name, reason):
+    """
+    :param req_name: the name of the requirement.
+    :param reason: the reason the requirement is being processed as
+        pyproject.toml-style.
+    """
+    message = (
+        'Error installing {!r}: editable mode is not supported for '
+        'pyproject.toml-style projects. This project is being processed '
+        'as pyproject.toml-style because {}. '
+        'See PEP 517 for the relevant specification.'
+    ).format(req_name, reason)
+    return InstallationError(message)
+
+
 def resolve_pyproject_toml(
-    build_system,  # type: Optional[Dict[str, str]]
+    build_system,  # type: Optional[Dict[str, Any]]
     has_pyproject,  # type: bool
     has_setup,  # type: bool
     use_pep517,  # type: Optional[bool]
+    editable,  # type: bool
     req_name,  # type: str
 ):
     # type: (...) -> Optional[Tuple[List[str], str, List[str]]]
@@ -67,6 +83,7 @@ def resolve_pyproject_toml(
     :param has_setup: whether the project has a setup.py file.
     :param use_pep517: whether the user requested PEP 517 processing.  None
         means the user didn't explicitly specify.
+    :param editable: whether editable mode was requested for the requirement.
     :param req_name: the name of the requirement we're processing (for
         error reporting).
     """
@@ -82,6 +99,10 @@ def resolve_pyproject_toml(
                 "Disabling PEP 517 processing is invalid: "
                 "project does not have a setup.py"
             )
+        if editable:
+            raise make_editable_error(
+                req_name, 'it has a pyproject.toml file and no setup.py'
+            )
         use_pep517 = True
     elif build_system and "build-backend" in build_system:
         if use_pep517 is not None and not use_pep517:
@@ -92,7 +113,18 @@ def resolve_pyproject_toml(
                     build_system["build-backend"]
                 )
             )
+        if editable:
+            reason = (
+                'it has a pyproject.toml file with a "build-backend" key '
+                'in the "build_system" value'
+            )
+            raise make_editable_error(req_name, reason)
         use_pep517 = True
+    elif use_pep517:
+        if editable:
+            raise make_editable_error(
+                req_name, 'PEP 517 processing was explicitly requested'
+            )
 
     # If we haven't worked out whether to use PEP 517 yet,
     # and the user hasn't explicitly stated a preference,
@@ -175,6 +207,7 @@ def resolve_pyproject_toml(
 
 def load_pyproject_toml(
     use_pep517,  # type: Optional[bool]
+    editable,  # type: bool
     pyproject_toml,  # type: str
     setup_py,  # type: str
     req_name  # type: str
@@ -185,6 +218,7 @@ def load_pyproject_toml(
     Parameters:
         use_pep517 - Has the user requested PEP 517 processing? None
                      means the user hasn't explicitly specified.
+        editable - Whether editable mode was requested for the requirement.
         pyproject_toml - Location of the project's pyproject.toml file
         setup_py - Location of the project's setup.py file
         req_name - The name of the requirement we're processing (for
@@ -212,5 +246,6 @@ def load_pyproject_toml(
         has_pyproject=has_pyproject,
         has_setup=has_setup,
         use_pep517=use_pep517,
+        editable=editable,
         req_name=req_name,
     )

src/pip/_internal/req/req_install.py

@@ -484,6 +484,7 @@ def load_pyproject_toml(self):
         """
         pep517_data = load_pyproject_toml(
             self.use_pep517,
+            self.editable,
             self.pyproject_toml,
             self.setup_py,
             str(self)

tests/unit/test_pep517.py

@@ -1,9 +1,69 @@
 import pytest
 
 from pip._internal.exceptions import InstallationError
+from pip._internal.pyproject import resolve_pyproject_toml
 from pip._internal.req import InstallRequirement
 
 
+@pytest.mark.parametrize('editable', [False, True])
+def test_resolve_pyproject_toml__pep_517_optional(editable):
+    """
+    Test resolve_pyproject_toml() when has_pyproject=True but the source
+    tree isn't pyproject.toml-style per PEP 517.
+    """
+    actual = resolve_pyproject_toml(
+        build_system=None,
+        has_pyproject=True,
+        has_setup=True,
+        use_pep517=None,
+        editable=editable,
+        req_name='my-package',
+    )
+    expected = (
+        ['setuptools>=40.8.0', 'wheel'],
+        'setuptools.build_meta:__legacy__',
+        [],
+    )
+    assert actual == expected
+
+
+@pytest.mark.parametrize(
+    'has_pyproject, has_setup, use_pep517, build_system, expected_err', [
+        # Test pyproject.toml with no setup.py.
+        (True, False, None, None, 'has a pyproject.toml file and no setup.py'),
+        # Test "build-backend" present.
+        (True, True, None, {'build-backend': 'foo'},
+         'has a pyproject.toml file with a "build-backend" key'),
+        # Test explicitly requesting PEP 517 processing.
+        (True, True, True, None,
+         'PEP 517 processing was explicitly requested'),
+    ]
+)
+def test_resolve_pyproject_toml__editable_and_pep_517_required(
+    has_pyproject, has_setup, use_pep517, build_system, expected_err,
+):
+    """
+    Test that passing editable=True raises an error if PEP 517 processing
+    is required.
+    """
+    with pytest.raises(InstallationError) as excinfo:
+        resolve_pyproject_toml(
+            build_system=build_system,
+            has_pyproject=has_pyproject,
+            has_setup=has_setup,
+            use_pep517=use_pep517,
+            editable=True,
+            req_name='my-package',
+        )
+    err_args = excinfo.value.args
+    assert len(err_args) == 1
+    msg = err_args[0]
+    assert msg.startswith(
+        "Error installing 'my-package': editable mode is not supported"
+    )
+    assert expected_err in msg, 'full message: {}'.format(msg)
+
+
 @pytest.mark.parametrize(('source', 'expected'), [
     ("pep517_setup_and_pyproject", True),
     ("pep517_setup_only", False),