Add editable strategy based on a link tree

- Add implementation of editable strategy based on a link tree
  - This is the `strict` implementation.
  - Only files are linked, not directories.
    - This approach makes it possible to use harlinks when softlinks are not
      available (e.g. Windows)
    - It also guarantees files that would not be part of the final wheel are
      not available in the editable install.
- Add non-editable files to the produced wheel wheel (e.g. `headers`,
  `scripts`, `data`)

Author: abravalheri

setuptools/command/build_ext.py

@@ -3,7 +3,6 @@
 import itertools
 from importlib.machinery import EXTENSION_SUFFIXES
 from distutils.command.build_ext import build_ext as _du_build_ext
-from distutils.file_util import copy_file
 from distutils.ccompiler import new_compiler
 from distutils.sysconfig import customize_compiler, get_config_var
 from distutils.errors import DistutilsError
@@ -96,10 +95,7 @@ def copy_extensions_to_source(self):
             # Always copy, even if source is older than destination, to ensure
             # that the right extensions for the current Python/platform are
             # used.
-            copy_file(
-                src_filename, dest_filename, verbose=self.verbose,
-                dry_run=self.dry_run
-            )
+            build_py.copy_file(src_filename, dest_filename)
             if ext._needs_stub:
                 self.write_stub(package_dir or os.curdir, ext, True)
 

setuptools/command/build_py.py

@@ -36,6 +36,17 @@ def finalize_options(self):
         if 'data_files' in self.__dict__:
             del self.__dict__['data_files']
         self.__updated_files = []
+        self.use_links = None
+
+    def copy_file(self, infile, outfile, preserve_mode=1, preserve_times=1,
+                  link=None, level=1):
+        # Overwrite base class to allow using links
+        link = getattr(self, "use_links", None) if link is None else link
+        if link:
+            infile = str(Path(infile).resolve())
+            outfile = str(Path(outfile).resolve())
+        return super().copy_file(infile, outfile, preserve_mode,
+                                 preserve_times, link, level)
 
     def run(self):
         """Build modules, packages, and copy data files to build directory"""