feat(sdist): dereference symlinks by default

README.md

@@ -202,6 +202,9 @@ sdist.reproducible = true
 # If set to True, CMake will be run before building the SDist.
 sdist.cmake = false
 
+# Resolve symlinks in the SDist, copying file contents instead of storing symlinks.
+sdist.resolve-symlinks = true
+
 # A list of packages to auto-copy into the wheel.
 wheel.packages = ["src/<package>", "python/<package>", "<package>"]
 

docs/reference/configs.md

@@ -493,6 +493,14 @@ print(mk_skbuild_docs())
   ``SOURCE_DATE_EPOCH`` will be used for timestamps, or a fixed value if not set.
 ```
 
+```{eval-rst}
+.. confval:: sdist.resolve-symlinks
+  :type: ``bool``
+  :default: true
+
+  Resolve symlinks in the SDist, copying file contents instead of storing symlinks.
+```
+
 ## search
 
 ```{eval-rst}

src/scikit_build_core/build/sdist.py

@@ -138,7 +138,12 @@ def build_sdist(
             )
         )
         tar = stack.enter_context(
-            tarfile.TarFile(fileobj=gzip_container, mode="w", format=tarfile.PAX_FORMAT)
+            tarfile.TarFile(
+                fileobj=gzip_container,
+                mode="w",
+                format=tarfile.PAX_FORMAT,
+                dereference=settings.sdist.resolve_symlinks,
+            )
         )
         assert settings.sdist.inclusion_mode is not None
         paths = sorted(

src/scikit_build_core/resources/scikit-build.schema.json

@@ -189,6 +189,11 @@
           "type": "boolean",
           "default": false,
           "description": "If set to True, CMake will be run before building the SDist."
+        },
+        "resolve-symlinks": {
+          "type": "boolean",
+          "default": true,
+          "description": "Resolve symlinks in the SDist, copying file contents instead of storing symlinks."
         }
       }
     },

src/scikit_build_core/settings/skbuild_model.py

@@ -262,6 +262,11 @@ class SDistSettings:
     If set to True, CMake will be run before building the SDist.
     """
 
+    resolve_symlinks: bool = True
+    """
+    Resolve symlinks in the SDist, copying file contents instead of storing symlinks.
+    """
+
 
 @dataclasses.dataclass
 class WheelSettings:

tests/test_pep517_sdist_symlink.py

@@ -0,0 +1,50 @@
+from __future__ import annotations
+
+import tarfile
+from pathlib import Path
+
+import pytest
+
+from scikit_build_core.build import build_sdist
+
+
+@pytest.fixture
+def can_symlink() -> None:
+    """Skip the test if symlinks are not supported on this OS."""
+    try:
+        Path("_symlink_check").symlink_to("_symlink_check_target")
+    except OSError:
+        pytest.skip(
+            "Creating symlinks is not supported/allowed on this OS without privileges"
+        )
+    else:
+        Path("_symlink_check").unlink(missing_ok=True)
+
+
+@pytest.mark.usefixtures("package_simple_pyproject_ext", "can_symlink")
+@pytest.mark.parametrize(
+    ("config_settings", "expected_type"),
+    [
+        pytest.param({}, "reg", id="dereference_default"),
+        pytest.param({"sdist.resolve-symlinks": "false"}, "sym", id="no_dereference"),
+    ],
+)
+def test_pep517_sdist_symlink(
+    tmp_path: Path,
+    config_settings: dict[str, list[str] | str],
+    expected_type: str,
+) -> None:
+    Path("CMakeLists_link.txt").symlink_to("CMakeLists.txt")
+
+    out = build_sdist(str(tmp_path), config_settings=config_settings or None)
+
+    with tarfile.open(tmp_path / out, "r:gz") as tar:
+        link_member = tar.getmember("cmake_example-0.0.1/CMakeLists_link.txt")
+        if expected_type == "reg":
+            assert link_member.isreg(), (
+                "The symlink should have been stored as a regular file"
+            )
+        else:
+            assert link_member.issym(), (
+                "The symlink should have been stored as a symlink"
+            )