poetry: expose build-system dependencies

src/poetry/core/poetry.py

@@ -1,12 +1,18 @@
 from __future__ import annotations
 
+import contextlib
+
+from pathlib import Path
 from typing import TYPE_CHECKING
 from typing import Any
 
+from poetry.core.packages.dependency import Dependency
+from poetry.core.packages.directory_dependency import DirectoryDependency
+from poetry.core.packages.file_dependency import FileDependency
+from poetry.core.utils.helpers import canonicalize_name
 
-if TYPE_CHECKING:
-    from pathlib import Path
 
+if TYPE_CHECKING:
     from poetry.core.packages.project_package import ProjectPackage
     from poetry.core.pyproject.toml import PyProjectTOML
     from poetry.core.toml import TOMLFile
@@ -24,6 +30,7 @@ def __init__(
         self._pyproject = PyProjectTOML(file)
         self._package = package
         self._local_config = local_config
+        self._build_system_dependencies: list[Dependency] | None = None
 
     @property
     def pyproject(self) -> PyProjectTOML:
@@ -43,3 +50,35 @@ def local_config(self) -> dict[str, Any]:
 
     def get_project_config(self, config: str, default: Any = None) -> Any:
         return self._local_config.get("config", {}).get(config, default)
+
+    @property
+    def build_system_dependencies(self) -> list[Dependency]:
+        if self._build_system_dependencies is None:
+            build_system = self.pyproject.build_system
+            self._build_system_dependencies = []
+
+            for requirement in build_system.requires:
+                dependency = None
+                try:
+                    dependency = Dependency.create_from_pep_508(requirement)
+                except ValueError:
+                    # PEP 517 requires can be path if not PEP 508
+                    path = Path(requirement)
+
+                    with contextlib.suppress(OSError):
+                        # suppress OSError for compatibility with Python < 3.8
+                        # https://docs.python.org/3/library/pathlib.html#methods
+                        if path.is_file():
+                            dependency = FileDependency(
+                                name=canonicalize_name(path.name), path=path
+                            )
+                        elif path.is_dir():
+                            dependency = DirectoryDependency(
+                                name=canonicalize_name(path.name), path=path
+                            )
+
+                # skip since we could not determine requirement
+                if dependency:
+                    self._build_system_dependencies.append(dependency)
+
+        return self._build_system_dependencies

tests/test_factory.py

@@ -6,6 +6,7 @@
 import pytest
 
 from poetry.core.factory import Factory
+from poetry.core.pyproject.tables import BuildSystem
 from poetry.core.semver.helpers import parse_constraint
 from poetry.core.toml import TOMLFile
 
@@ -320,3 +321,18 @@ def test_create_dependency_marker_variants(
     assert dep.python_versions == exp_python
     assert dep.python_constraint == parse_constraint(exp_python)
     assert str(dep.marker) == exp_marker
+
+
+@pytest.mark.parametrize(
+    "project, requries",
+    [
+        ("sample_project", set(BuildSystem().requires)),
+        ("project_with_build_system_requires", {"poetry-core", "cython"}),
+    ],
+)
+def test_poetry_build_system_dependencies(project: str, requries: set[str]):
+    poetry = Factory().create_poetry(fixtures_dir / "sample_project")
+
+    assert set(BuildSystem().requires) == {
+        dependency.name for dependency in poetry.build_system_dependencies
+    }