Add link check to `make sdist`.

This will cause `make sdist` to fail on platforms which create
hard links of symbolic links as regular files, such as MacOS (Darwin).

This prevents accidental creation of an sdist tarball without
the necessary symbolic links.

1 files changed, 51 insertions, 0 deletions

diff --git a/packaging/sdist/check-link-behavior.py b/packaging/sdist/check-link-behavior.py
new file mode 100755
index 0000000000..34e05023d4
--- /dev/null
+++ b/packaging/sdist/check-link-behavior.py
@@ -0,0 +1,51 @@
+#!/usr/bin/env python
+"""Checks for link behavior required for sdist to retain symlinks."""
+
+from __future__ import (absolute_import, division, print_function)
+
+__metaclass__ = type
+
+import os
+import platform
+import shutil
+import sys
+import tempfile
+
+
+def main():
+    """Main program entry point."""
+    temp_dir = tempfile.mkdtemp()
+
+    target_path = os.path.join(temp_dir, 'file.txt')
+    symlink_path = os.path.join(temp_dir, 'symlink.txt')
+    hardlink_path = os.path.join(temp_dir, 'hardlink.txt')
+
+    try:
+        with open(target_path, 'w'):
+            pass
+
+        os.symlink(target_path, symlink_path)
+        os.link(symlink_path, hardlink_path)
+
+        if not os.path.islink(symlink_path):
+            abort('Symbolic link not created.')
+
+        if not os.path.islink(hardlink_path):
+            # known issue on MacOS (Darwin)
+            abort('Hard link of symbolic link created as a regular file.')
+    finally:
+        shutil.rmtree(temp_dir)
+
+
+def abort(reason):
+    """
+    :type reason: str
+    """
+    sys.exit('ERROR: %s\n'
+             'This will prevent symbolic links from being preserved in the resulting tarball.\n'
+             'Aborting creation of sdist on platform: %s'
+             % (reason, platform.system()))
+
+
+if __name__ == '__main__':
+    main()