fix sourcing empty workspace built with --merge-install (#179)

* fix sourcing empty workspace with merge install

Signed-off-by: Mikael Arguedas <mikael.arguedas@gmail.com>

* update test for empty workspaces

Signed-off-by: Mikael Arguedas <mikael.arguedas@gmail.com>

* mock -> check

Signed-off-by: Mikael Arguedas <mikael.arguedas@gmail.com>

colcon_core/shell/template/prefix_util.py

@@ -38,6 +38,9 @@ def get_packages(prefix_path, merged_install):
     # must match colcon_core.location.get_relative_package_index_path()
     subdirectory = 'share/colcon-core/packages'
     if merged_install:
+        # return if workspace is empty
+        if not (prefix_path / subdirectory).is_dir():
+            return packages
         # find all files in the subdirectory
         for p in (prefix_path / subdirectory).iterdir():
             if not p.is_file():

test/test_shell_template_prefix_util.py

@@ -29,6 +29,10 @@ def test_get_packages():
     with TemporaryDirectory(prefix='test_colcon_') as prefix_path:
         prefix_path = Path(prefix_path)
 
+        # check no packages in not merged install layout
+        packages = get_packages(prefix_path, False)
+        assert packages == {}
+
         # mock packages in not merged install layout
         subdirectory = get_relative_package_index_path()
         for pkg_name in ('pkgA', 'pkgB'):
@@ -39,6 +43,10 @@ def test_get_packages():
         (prefix_path / '.hidden_dir').mkdir()
         (prefix_path / 'dummy_file').write_text('')
 
+        # check no packages in merged install layout
+        packages = get_packages(prefix_path, True)
+        assert packages == {}
+
         # mock packages in merged install layout
         (prefix_path / subdirectory).mkdir(parents=True)
         (prefix_path / subdirectory / 'pkgB').write_text('')