Support building dists from preexisting setup.py.

[ci skip-rust]

[ci skip-build-wheels]

src/python/pants/backend/python/goals/setup_py.py

@@ -71,27 +71,26 @@
 logger = logging.getLogger(__name__)
 
 
-class InvalidSetupPyArgs(Exception):
+class SetupPyError(Exception):
+    def __init__(self, msg: str):
+        super().__init__(f"{msg} See {bracketed_docs_url('python-distributions')}.")
+
+
+class InvalidSetupPyArgs(SetupPyError):
     """Indicates invalid arguments to setup.py."""
 
 
-class TargetNotExported(Exception):
+class TargetNotExported(SetupPyError):
     """Indicates a target that was expected to be exported is not."""
 
 
-class InvalidEntryPoint(Exception):
+class InvalidEntryPoint(SetupPyError):
     """Indicates that a specified binary entry point was invalid."""
 
 
-class OwnershipError(Exception):
+class OwnershipError(SetupPyError):
     """An error related to target ownership calculation."""
 
-    def __init__(self, msg: str):
-        super().__init__(
-            f"{msg} See {bracketed_docs_url('python-distributions')} for "
-            f"how python_library targets are mapped to distributions."
-        )
-
 
 class NoOwnerError(OwnershipError):
     """Indicates an exportable target has no owning exported target."""
@@ -201,8 +200,14 @@ def __init__(
         self, kwargs: Mapping[str, Any], *, address: Address, _allow_banned_keys: bool = False
     ) -> None:
         super().__init__()
+        if "name" not in kwargs:
+            raise InvalidSetupPyArgs(
+                f"Missing a `name` kwarg in the `provides` field for {address}."
+            )
         if "version" not in kwargs:
-            raise ValueError(f"Missing a `version` kwarg in the `provides` field for {address}.")
+            raise InvalidSetupPyArgs(
+                f"Missing a `version` kwarg in the `provides` field for {address}."
+            )
 
         if not _allow_banned_keys:
             for arg in {
@@ -274,9 +279,14 @@ def __init__(self, kwargs: Mapping[str, Any], *, address: Address) -> None:
 
 @dataclass(frozen=True)
 class SetupPyChroot:
-    """A chroot containing a generated setup.py and the sources it operates on."""
+    """A chroot containing a setup.py and the sources it operates on."""
 
     digest: Digest
+    setup_script: str  # The path of the setup script within the digest.
+
+    # Note that this field is merely informational, used primarily in tests, and
+    # to construct the chroot name from the name and version kwargs, when setup is
+    # run with no args.
     setup_kwargs: FinalizedSetupKwargs
 
 
@@ -350,7 +360,7 @@ def validate_commands(commands: Tuple[str, ...]):
     # TODO: A `publish` rule, that can invoke Twine to do the actual uploading.
     #  See https://github.com/pantsbuild/pants/issues/8935.
     if "upload" in commands or "register" in commands:
-        raise InvalidSetupPyArgs("Cannot use the `upload` or `register` setup.py commands")
+        raise InvalidSetupPyArgs("Cannot use the `upload` or `register` setup.py commands.")
 
 
 @rule
@@ -422,7 +432,7 @@ async def run_setup_py(req: RunSetupPyRequest, setuptools: Setuptools) -> RunSet
         ProcessResult,
         VenvPexProcess(
             setuptools_pex,
-            argv=("setup.py", *req.args),
+            argv=(req.chroot.setup_script, *req.args),
             input_digest=req.chroot.digest,
             # setuptools commands that create dists write them to the distdir.
             # TODO: Could there be other useful files to capture?
@@ -490,6 +500,23 @@ async def generate_chroot(request: SetupPyChrootRequest) -> SetupPyChroot:
     target = exported_target.target
     resolved_setup_kwargs = await Get(SetupKwargs, ExportedTarget, exported_target)
     setup_kwargs = resolved_setup_kwargs.kwargs.copy()
+
+    setup_script = setup_kwargs.pop("setup_script", None)
+    if setup_script:
+        # The target points to an existing setup.py script, so use that.
+        invalid_keys = set(setup_kwargs.keys()) - {"name", "version"}
+        if invalid_keys:
+            raise InvalidSetupPyArgs(
+                f"The `provides` field in {exported_addr} specifies a setup_script kwarg, so it "
+                f"must only specify the name and version kwargs, but it also specified "
+                f"{','.join(sorted(invalid_keys))}."
+            )
+        return SetupPyChroot(
+            sources.digest, setup_script, FinalizedSetupKwargs(setup_kwargs, address=target.address)
+        )
+
+    # There is no existing setup.py script, so we generate one.
+
     # NB: We are careful to not overwrite these values, but we also don't expect them to have been
     # set. The user must have have gone out of their way to use a `SetupKwargs` plugin, and to have
     # specified `SetupKwargs(_allow_banned_keys=True)`.
@@ -562,7 +589,9 @@ async def generate_chroot(request: SetupPyChrootRequest) -> SetupPyChroot:
     )
 
     chroot_digest = await Get(Digest, MergeDigests((src_digest, extra_files_digest)))
-    return SetupPyChroot(chroot_digest, FinalizedSetupKwargs(setup_kwargs, address=target.address))
+    return SetupPyChroot(
+        chroot_digest, "setup.py", FinalizedSetupKwargs(setup_kwargs, address=target.address)
+    )
 
 
 @rule

src/python/pants/backend/python/goals/setup_py_test.py

@@ -81,9 +81,11 @@ def is_applicable(cls, _) -> bool:
 
 @rule
 def setup_kwargs_plugin(request: PluginSetupKwargsRequest) -> SetupKwargs:
-    return SetupKwargs(
-        {**request.explicit_kwargs, "plugin_demo": "hello world"}, address=request.target.address
-    )
+    if "setup_script" in request.explicit_kwargs:
+        kwargs = request.explicit_kwargs
+    else:
+        kwargs = {**request.explicit_kwargs, "plugin_demo": "hello world"}
+    return SetupKwargs(kwargs, address=request.target.address)
 
 
 @pytest.fixture
@@ -131,6 +133,79 @@ def assert_chroot_error(rule_runner: RuleRunner, addr: Address, exc_cls: Type[Ex
     assert type(ex.wrapped_exceptions[0]) == exc_cls
 
 
+def test_use_existing_setup_script(chroot_rule_runner) -> None:
+    chroot_rule_runner.add_to_build_file("src/python/foo/bar", "python_library()")
+    chroot_rule_runner.create_file("src/python/foo/bar/__init__.py")
+    chroot_rule_runner.create_file("src/python/foo/bar/bar.py")
+    # Add a `.pyi` stub file to ensure we include it in the final result.
+    chroot_rule_runner.create_file("src/python/foo/bar/bar.pyi")
+    chroot_rule_runner.add_to_build_file(
+        "src/python/foo/resources", 'resources(sources=["js/code.js"])'
+    )
+    chroot_rule_runner.create_file("src/python/foo/resources/js/code.js")
+    chroot_rule_runner.add_to_build_file("files", 'files(sources=["README.txt"])')
+    chroot_rule_runner.create_file("files/README.txt")
+    chroot_rule_runner.add_to_build_file(
+        "src/python/foo",
+        textwrap.dedent(
+            """
+            python_distribution(
+                name='foo-dist',
+                dependencies=[
+                    ':foo',
+                ],
+                provides=setup_py(
+                    setup_script='src/python/foo/setup.py',
+                    name='foo', version='1.2.3'
+                )
+            )
+
+            python_library(
+                dependencies=[
+                    'src/python/foo/bar',
+                    'src/python/foo/resources',
+                    'files',
+                ]
+            )
+            """
+        ),
+    )
+    chroot_rule_runner.create_file("src/python/foo/__init__.py", _namespace_decl)
+    chroot_rule_runner.create_file("src/python/foo/foo.py")
+    chroot_rule_runner.create_file(
+        "src/python/foo/setup.py",
+        textwrap.dedent(
+            """
+        from setuptools import setup
+
+        setup(
+            name = "foo",
+            version = "1.2.3",
+            packages = ["foo"],
+        )
+    """
+        ),
+    )
+    assert_chroot(
+        chroot_rule_runner,
+        [
+            "files/README.txt",
+            "foo/bar/__init__.py",
+            "foo/bar/bar.py",
+            "foo/bar/bar.pyi",
+            "foo/resources/js/code.js",
+            "foo/__init__.py",
+            "foo/foo.py",
+            "foo/setup.py",
+        ],
+        {
+            "name": "foo",
+            "version": "1.2.3",
+        },
+        Address("src/python/foo", target_name="foo-dist"),
+    )
+
+
 def test_generate_chroot(chroot_rule_runner: RuleRunner) -> None:
     chroot_rule_runner.add_to_build_file(
         "src/python/foo/bar/baz",