fix: follow symlinks when making SDists (#362)

Fixing #359.


---------

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

Author: henryiii

src/scikit_build_core/build/_file_processor.py

@@ -41,7 +41,7 @@ def each_unignored_file(
     exclude_spec = pathspec.GitIgnoreSpec.from_lines(exclude_lines)
     include_spec = pathspec.GitIgnoreSpec.from_lines(include)
 
-    for dirpath, _, filenames in os.walk(str(starting_path)):
+    for dirpath, _, filenames in os.walk(str(starting_path), followlinks=True):
         all_paths = (Path(dirpath) / fn for fn in filenames)
         paths = (
             p

tests/test_file_processor.py

@@ -0,0 +1,53 @@
+from __future__ import annotations
+
+import sys
+from pathlib import Path
+
+import pytest
+
+from scikit_build_core.build._file_processor import each_unignored_file
+
+
+@pytest.mark.skipif(
+    sys.version_info < (3, 8) and sys.platform.startswith("win"),
+    reason="Python 3.8+ required for symlinks on Windows",
+)
+@pytest.mark.skipif(
+    sys.implementation.name == "pypy" and sys.platform.startswith("win"),
+    reason="PyPy on Windows does not support symlinks",
+)
+def test_on_each_with_symlink(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> None:
+    """
+    Test that each_unignored_file() does not follow symlinks.
+    """
+    monkeypatch.chdir(tmp_path)
+    # Set up a gitignore
+    gitignore = Path(".gitignore")
+    gitignore.write_text("/hidden_dir")
+    # Create a directory with a symlink to a file in the same directory
+    dir = Path("dir")
+    dir.mkdir()
+    file1 = dir / "file"
+    file1.write_text("content")
+    file2 = dir / "link"
+    file2.symlink_to("file")
+    hidden_dir = Path("hidden_dir")
+    hidden_dir.mkdir()
+    hidden_file = hidden_dir / "file2"
+    hidden_file.write_text("content2")
+    exposed_symlink = dir / "exposed_symlink"
+    exposed_symlink.symlink_to("../hidden_dir")
+
+    if (
+        sys.platform.startswith("win")
+        and not exposed_symlink.joinpath("file2").is_file()
+    ):
+        pytest.skip("Windows symlink support not available")
+
+    # Test that each_unignored_file() follows the symlink
+    assert sorted(each_unignored_file(Path("."))) == [
+        gitignore,
+        exposed_symlink / "file2",
+        file1,
+        file2,
+    ]