Support editable installs of Cython pxd files

src/scikit_build_core/build/wheel.py

@@ -29,7 +29,7 @@
 from .generate import generate_file_contents
 
 if TYPE_CHECKING:
-    from collections.abc import Sequence
+    from collections.abc import Iterable, Sequence
 
     from ..settings.skbuild_model import ScikitBuildSettings
 
@@ -50,6 +50,7 @@ def _make_editable(
     reload_dir: Path | None,
     settings: ScikitBuildSettings,
     wheel: WheelWriter,
+    packages: Iterable[str],
 ) -> None:
     modules = mapping_to_modules(mapping, libdir)
     installed = libdir_to_installed(libdir)
@@ -68,9 +69,14 @@ def _make_editable(
         f"_{name}_editable.py",
         editable_txt.encode(),
     )
+    # Support Cython by adding the source directory directly to the path.
+    # This is necessary because Cython does not support sys.meta_path for
+    # cimports (as of 3.0.5).
+    import_strings = [f"import _{name}_editable", *packages, ""]
+    pth_import_paths = "\n".join(import_strings)
     wheel.writestr(
         f"_{name}_editable.pth",
-        f"import _{name}_editable\n".encode(),
+        pth_import_paths.encode(),
     )
 
 
@@ -341,6 +347,7 @@ def _build_wheel_impl(
         ) as wheel:
             wheel.build(wheel_dirs)
 
+            str_pkgs = (str(Path.cwd().joinpath(p).parent.resolve()) for p in packages)
             if editable and settings.editable.mode == "redirect":
                 reload_dir = build_dir.resolve() if settings.build_dir else None
 
@@ -353,15 +360,13 @@ def _build_wheel_impl(
                     settings=settings,
                     wheel=wheel,
                     name=normalized_name,
+                    packages=str_pkgs,
                 )
             elif editable and settings.editable.mode == "inplace":
                 if not packages:
                     msg = "Editable inplace mode requires at least one package"
                     raise AssertionError(msg)
 
-                str_pkgs = (
-                    str(Path.cwd().joinpath(p).parent.resolve()) for p in packages
-                )
                 wheel.writestr(
                     f"_{normalized_name}_editable.pth",
                     "\n".join(str_pkgs).encode(),

tests/conftest.py

@@ -50,6 +50,7 @@ def pep518_wheelhouse(tmp_path_factory: pytest.TempPathFactory) -> Path:
     )
     packages = [
         "build",
+        "cython",
         "hatchling",
         "pip>=23",
         "pybind11",

tests/packages/cython_pxd_editable/pkg1/CMakeLists.txt

@@ -0,0 +1,21 @@
+cmake_minimum_required(VERSION 3.15)
+project(${SKBUILD_PROJECT_NAME} LANGUAGES C)
+
+find_package(
+  Python
+  COMPONENTS Interpreter Development.Module
+  REQUIRED)
+
+find_program(CYTHON "cython")
+
+add_custom_command(
+  OUTPUT src/pkg1/one.c
+  DEPENDS src/pkg1/one.pyx
+  VERBATIM
+  COMMAND "${CYTHON}" "${CMAKE_CURRENT_SOURCE_DIR}/src/pkg1/one.pyx"
+          --output-file "${CMAKE_CURRENT_BINARY_DIR}/src/pkg1/one.c")
+
+python_add_library(one MODULE "${CMAKE_CURRENT_BINARY_DIR}/src/pkg1/one.c"
+                   WITH_SOABI)
+
+install(TARGETS one DESTINATION pkg1/)

tests/packages/cython_pxd_editable/pkg1/pyproject.toml

@@ -0,0 +1,13 @@
+[build-system]
+build-backend = "scikit_build_core.build"
+requires = [
+    "cython>=3.0.0",
+    "scikit-build-core",
+]
+
+[project]
+name = "pkg1"
+version = "1.0.0"
+
+[tool.scikit-build]
+wheel.packages = ["src/pkg1"]

tests/packages/cython_pxd_editable/pkg1/src/pkg1/one.pxd

@@ -0,0 +1 @@
+cdef int one()

tests/packages/cython_pxd_editable/pkg1/src/pkg1/one.pyx

@@ -0,0 +1,2 @@
+cdef int one():
+    return 1

tests/packages/cython_pxd_editable/pkg2/CMakeLists.txt

@@ -0,0 +1,21 @@
+cmake_minimum_required(VERSION 3.15)
+project(${SKBUILD_PROJECT_NAME} LANGUAGES C)
+
+find_package(
+  Python
+  COMPONENTS Interpreter Development.Module
+  REQUIRED)
+
+find_program(CYTHON "cython")
+
+add_custom_command(
+  OUTPUT src/pkg2/two.c
+  DEPENDS src/pkg2/two.pyx
+  VERBATIM
+  COMMAND "${CYTHON}" "${CMAKE_CURRENT_SOURCE_DIR}/src/pkg2/two.pyx"
+          --output-file "${CMAKE_CURRENT_BINARY_DIR}/src/pkg2/two.c")
+
+python_add_library(two MODULE "${CMAKE_CURRENT_BINARY_DIR}/src/pkg2/two.c"
+                   WITH_SOABI)
+
+install(TARGETS two DESTINATION pkg2/)

tests/packages/cython_pxd_editable/pkg2/pyproject.toml

@@ -0,0 +1,13 @@
+[build-system]
+build-backend = "scikit_build_core.build"
+requires = [
+    "cython>=3.0.0",
+    "scikit-build-core",
+]
+
+[project]
+name = "pkg2"
+version = "1.0.0"
+
+[tool.scikit-build]
+wheel.packages = ["src/pkg2"]

tests/packages/cython_pxd_editable/pkg2/src/pkg2/two.pyx

@@ -0,0 +1,4 @@
+from pkg1.one cimport one
+
+cdef int two():
+    return one() + one()

tests/test_editable.py

@@ -2,6 +2,7 @@
 from pathlib import Path
 
 import pytest
+from conftest import PackageInfo, process_package
 
 
 @pytest.mark.compile()
@@ -48,3 +49,51 @@ def test_navigate_editable(isolated, isolate, package):
 
     value = isolated.execute("import shared_pkg; shared_pkg.read_c_generated_txt()")
     assert value == "Some_value_C"
+
+
+@pytest.mark.compile()
+@pytest.mark.configure()
+@pytest.mark.integration()
+@pytest.mark.parametrize(
+    ("editable", "editable_mode"), [(False, ""), (True, "redirect"), (True, "inplace")]
+)
+def test_cython_pxd(monkeypatch, tmp_path, editable, editable_mode, isolated):
+    editable_flag = ["-e"] if editable else []
+
+    config_mode_flags = []
+    if editable:
+        config_mode_flags.append(f"--config-settings=editable.mode={editable_mode}")
+    if editable_mode != "inplace":
+        config_mode_flags.append("--config-settings=build-dir=build/{wheel_tag}")
+
+    package1 = PackageInfo(
+        "cython_pxd_editable/pkg1",
+    )
+    tmp_path1 = tmp_path / "pkg1"
+    tmp_path1.mkdir()
+    process_package(package1, tmp_path1, monkeypatch)
+
+    isolated.install("pip>23", "cython", "scikit-build-core[pyproject]")
+
+    isolated.install(
+        "-v",
+        *config_mode_flags,
+        "--no-build-isolation",
+        *editable_flag,
+        ".",
+    )
+
+    package2 = PackageInfo(
+        "cython_pxd_editable/pkg2",
+    )
+    tmp_path2 = tmp_path / "pkg2"
+    tmp_path2.mkdir()
+    process_package(package2, tmp_path2, monkeypatch)
+
+    isolated.install(
+        "-v",
+        *config_mode_flags,
+        "--no-build-isolation",
+        *editable_flag,
+        ".",
+    )