Implement a custom distutils command to symlink data_files (#592)

The default implementation of install_data will always copy files into
the destination directory. When we use the 'develop' command, we
actually need to specifically tell setuptools to do something with the
data_files or they will be ignored. Instead of telling setuptools to use
install_data as-is, we can implement a custom version of install_data
that will try to symlink the files instead.

colcon_core/distutils/commands/symlink_data.py

@@ -0,0 +1,26 @@
+# Copyright 2023 Open Source Robotics Foundation, Inc.
+# Licensed under the Apache License, Version 2.0
+
+from distutils.command.install_data import install_data
+import os
+
+
+class symlink_data(install_data):  # noqa: N801
+    """Like install_data, but symlink files instead of copying."""
+
+    def copy_file(self, src, dst, **kwargs):  # noqa: D102
+        if kwargs.get('link'):
+            return super().copy_file(src, dst, **kwargs)
+
+        if self.force:
+            # os.symlink fails if the destination exists as a regular file
+            if os.path.isdir(dst):
+                target = os.path.join(dst, os.path.basename(src))
+            else:
+                target = dst
+            if os.path.exists(dst) and not os.path.islink(dst):
+                os.remove(target)
+
+        kwargs['link'] = 'sym'
+        src = os.path.abspath(src)
+        return super().copy_file(src, dst, **kwargs)

colcon_core/task/python/build.py

@@ -118,13 +118,19 @@ async def build(self, *, additional_hooks=None):  # noqa: D102
                 # prevent installation of dependencies specified in setup.py
                 cmd.append('--single-version-externally-managed')
             self._append_install_layout(args, cmd)
+            if setup_py_data.get('data_files'):
+                cmd += ['install_data']
+                if rc is not None:
+                    cmd += ['--force']
             completed = await run(
                 self.context, cmd, cwd=args.path, env=env)
             if completed.returncode:
                 return completed.returncode
 
         else:
-            self._undo_install(pkg, args, setup_py_data, python_lib)
+            rc = self._undo_install(pkg, args, setup_py_data, python_lib)
+            if rc:
+                return rc
             temp_symlinks = self._symlinks_in_build(args, setup_py_data)
 
             # invoke `setup.py develop` step in build space
@@ -142,7 +148,9 @@ async def build(self, *, additional_hooks=None):  # noqa: D102
                     '--no-deps',
                 ]
                 if setup_py_data.get('data_files'):
-                    cmd += ['install_data']
+                    cmd += ['symlink_data']
+                    if rc is not None:
+                        cmd += ['--force']
                 completed = await run(
                     self.context, cmd, cwd=args.build_base, env=env)
             finally:
@@ -189,6 +197,12 @@ async def _get_available_commands(self, path, env):
         return commands
 
     async def _undo_develop(self, pkg, args, env):
+        """
+        Undo a previously run 'develop' command.
+
+        :returns: None if develop was not previously detected, otherwise
+                  an integer return code where zero indicates success.
+        """
         # undo previous develop if .egg-info is found and develop symlinks
         egg_info = os.path.join(
             args.build_base, '%s.egg-info' % pkg.name.replace('-', '_'))
@@ -207,6 +221,12 @@ async def _undo_develop(self, pkg, args, env):
             return completed.returncode
 
     def _undo_install(self, pkg, args, setup_py_data, python_lib):
+        """
+        Undo a previously run 'install' command.
+
+        :returns: None if install was not previously detected, otherwise
+                  an integer return code where zero indicates success.
+        """
         # undo previous install if install.log is found
         install_log = os.path.join(args.build_base, 'install.log')
         if not os.path.exists(install_log):
@@ -246,6 +266,7 @@ def _undo_install(self, pkg, args, setup_py_data, python_lib):
             with suppress(OSError):
                 os.rmdir(d)
         os.remove(install_log)
+        return 0
 
     def _symlinks_in_build(self, args, setup_py_data):
         items = ['setup.py']

setup.cfg

@@ -145,6 +145,8 @@ colcon_core.verb =
     test = colcon_core.verb.test:TestVerb
 console_scripts =
     colcon = colcon_core.command:main
+distutils.commands =
+    symlink_data = colcon_core.distutils.commands.symlink_data:symlink_data
 pytest11 =
     colcon_core_warnings_stderr = colcon_core.pytest.hooks