fix: build from sources when forcing build from source

.github/workflows/build.yml

@@ -128,8 +128,11 @@ jobs:
           name: cibw-sdist
           path: sdist
 
+      - name: Ensure Ninja not present on the system
+        run: if which ninja; then false; fi
+
       - name: Install SDist
-        run: pip install $(ls sdist/*.tar.gz)[test] -Ccmake.define.BUILD_CMAKE_FROM_SOURCE=OFF
+        run: pip install --no-binary=ninja $(ls sdist/*.tar.gz)[test] -Ccmake.define.BUILD_CMAKE_FROM_SOURCE=OFF
 
       - name: Test installed SDist
         run: pip check && pytest ./tests

_build_backend/backend.py

@@ -0,0 +1,17 @@
+from scikit_build_core import build as _orig
+
+prepare_metadata_for_build_wheel = _orig.prepare_metadata_for_build_wheel
+build_wheel = _orig.build_wheel
+build_sdist = _orig.build_sdist
+get_requires_for_build_sdist = _orig.get_requires_for_build_sdist
+
+def get_requires_for_build_wheel(config_settings=None):
+    packages_orig = _orig.get_requires_for_build_wheel(config_settings)
+    packages = []
+    for package in packages_orig:
+        package_name = package.lower().split(">")[0].strip()
+        if package_name == "ninja":
+            # never request ninja from the ninja build
+            continue
+        packages.append(package)
+    return packages

pyproject.toml

@@ -1,6 +1,7 @@
 [build-system]
-requires = ["scikit-build-core"]
-build-backend = "scikit_build_core.build"
+requires = ["scikit-build-core>=0.10"]
+build-backend = "backend"
+backend-path = ["_build_backend"]
 
 [project]
 name = "ninja"
@@ -50,7 +51,8 @@ Homepage = "http://ninja-build.org/"
 "Source Code" = "https://github.com/scikit-build/ninja-python-distributions"
 
 [tool.scikit-build]
-minimum-version = "0.9"
+minimum-version = "build-system.requires"
+ninja.make-fallback = true
 build-dir = "build/{wheel_tag}"
 wheel.py-api = "py3"
 wheel.expand-macos-universal-tags = true