Support getting files in the build tree from editable installs

src/scikit_build_core/resources/_editable_redirect.py

@@ -1,6 +1,8 @@
 from __future__ import annotations
 
 import importlib.abc
+import importlib.machinery
+import importlib.readers  # Might be Python version specific?
 import importlib.util
 import os
 import subprocess
@@ -22,6 +24,27 @@ def __dir__() -> list[str]:
     return __all__
 
 
+# Note: This solution relies on importlib's call stack in Python 3.11. Python 3.9 looks
+# different, so might require a different solution, but I haven't gone deeper into that
+# yet since I don't have a solution for the 3.11 case yet anyway.
+class ScikitBuildRedirectingReader(importlib.readers.FileReader):
+    def files(self):
+        # ATTENTION: This is where the problem is. The expectation is that this returns
+        # a Traversable object. We could hack together an object that satisfies that
+        # API, but methods like `joinpath` don't have sensible implementations if
+        # `files` could return multiple paths instead of a single one. We could do some
+        # hackery to figure out which paths exist on the backend by hiding some internal
+        # representation that knows both possible roots and checks for existence when
+        # necessary, but that seriously violates the principle of least surprise for the
+        # user so I'd be quite skeptical.
+        return self.path
+
+
+class ScikitBuildRedirectingLoader(importlib.machinery.SourceFileLoader):
+    def get_resource_reader(self, module):
+        return ScikitBuildRedirectingReader(self)
+
+
 class ScikitBuildRedirectingFinder(importlib.abc.MetaPathFinder):
     def __init__(
         self,
@@ -92,13 +115,17 @@ def find_spec(
                 fullname,
                 os.path.join(self.dir, redir),
                 submodule_search_locations=submodule_search_locations,
+                loader=ScikitBuildRedirectingLoader(
+                    fullname, os.path.join(self.dir, redir)
+                ),
             )
         if fullname in self.known_source_files:
             redir = self.known_source_files[fullname]
             return importlib.util.spec_from_file_location(
                 fullname,
                 redir,
                 submodule_search_locations=submodule_search_locations,
+                loader=ScikitBuildRedirectingLoader(fullname, redir),
             )
         return None
 

tests/packages/importlib_editable/CMakeLists.txt

@@ -0,0 +1,13 @@
+cmake_minimum_required(VERSION 3.15...3.26)
+project(${SKBUILD_PROJECT_NAME} LANGUAGES C)
+
+find_package(
+  Python
+  COMPONENTS Interpreter Development.Module
+  REQUIRED)
+
+python_add_library(example MODULE example/example.c WITH_SOABI)
+
+install(TARGETS example DESTINATION example/)
+file(WRITE "${CMAKE_BINARY_DIR}/testfile" "This is the file")
+install(FILES "${CMAKE_BINARY_DIR}/testfile" DESTINATION example/)

tests/packages/importlib_editable/example/example.c

@@ -0,0 +1,25 @@
+#define PY_SSIZE_T_CLEAN
+#include <Python.h>
+
+float square(float x) { return x * x; }
+
+static PyObject *square_wrapper(PyObject *self, PyObject *args) {
+  float input, result;
+  if (!PyArg_ParseTuple(args, "f", &input)) {
+    return NULL;
+  }
+  result = square(input);
+  return PyFloat_FromDouble(result);
+}
+
+static PyMethodDef example_methods[] = {
+    {"square", square_wrapper, METH_VARARGS, "Square function"},
+    {NULL, NULL, 0, NULL}};
+
+static struct PyModuleDef example_module = {PyModuleDef_HEAD_INIT, "example",
+                                             NULL, -1, example_methods};
+
+/* name here must match extension name, with PyInit_ prefix */
+PyMODINIT_FUNC PyInit_example(void) {
+  return PyModule_Create(&example_module);
+}

tests/packages/importlib_editable/pyproject.toml

@@ -0,0 +1,10 @@
+[build-system]
+requires = ["scikit-build-core"]
+build-backend = "scikit_build_core.build"
+
+[project]
+name = "example"
+version = "0.0.1"
+
+[tool.scikit-build]
+build-dir = "build/{wheel_tag}"

tests/test_editable.py

@@ -1,4 +1,5 @@
 import sys
+import textwrap
 from pathlib import Path
 
 import pytest
@@ -105,3 +106,62 @@ def test_cython_pxd(monkeypatch, tmp_path, editable, editable_mode, isolated):
         *editable_flag,
         ".",
     )
+
+
+@pytest.mark.compile()
+@pytest.mark.configure()
+@pytest.mark.integration()
+@pytest.mark.parametrize(
+    ("editable", "editable_mode"), [(False, ""), (True, "redirect"), (True, "inplace")]
+)
+def test_importlib_resources(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}")
+
+    # Use a context so that we only change into the directory up until the point where
+    # we run the editable install. We do not want to be in that directory when importing
+    # to avoid importing the source directory instead of the installed package.
+    with monkeypatch.context() as m:
+        package1 = PackageInfo(
+            "importlib_editable",
+        )
+        process_package(package1, tmp_path, m)
+
+        ninja = [
+            "ninja"
+            for f in isolated.wheelhouse.iterdir()
+            if f.name.startswith("ninja-")
+        ]
+        cmake = [
+            "cmake"
+            for f in isolated.wheelhouse.iterdir()
+            if f.name.startswith("cmake-")
+        ]
+
+        isolated.install("pip>23")
+        isolated.install("scikit-build-core", *ninja, *cmake)
+
+        isolated.install(
+            "-v",
+            *config_mode_flags,
+            "--no-build-isolation",
+            *editable_flag,
+            ".",
+        )
+
+    value = isolated.execute(
+        textwrap.dedent(
+            """
+            import importlib.resources
+            import example
+            root = importlib.resources.files(example)
+            print(any('testfile' in str(x) for x in root.iterdir()))
+            """
+        )
+    )
+    assert value == "True"