Fix UnboundLocalError in `aiida.cmdline.utils.edit_multiline_templa…

…te` (#4436)

If `click.edit` returns a falsy value, the following conditional would
be skipped and the `value` variable would be undefined causing an
`UnboundLocalError` to be raised. This bug was reported by @blokhin but
the exact conditions under which it occurred are not clear.

Cherry-pick: 861a39f

aiida/cmdline/utils/multi_line_input.py

@@ -20,18 +20,19 @@ def edit_multiline_template(template_name, comment_marker='#=', extension=None,
     :param comment_marker: the set of symbols that mark a comment line that should be stripped from the final value
     :param extension: the file extension to give to the rendered template file.
     :param kwargs: keywords that will be passed to the template rendering engine.
-    :return: the final string value entered in the editor with all comment lines stripped.
+    :return: the final string value entered in the editor with all comment lines stripped or an empty string if the
+        ``click.edit`` returned ``None``.
     """
     from aiida.cmdline.utils.templates import env
     template = env.get_template(template_name)
     rendered = template.render(**kwargs)
     content = click.edit(rendered, extension=extension)
 
-    if content:
+    if content is not None:
         # Remove all comments, which are all lines that start with the comment marker
-        value = re.sub(r'(^' + re.escape(comment_marker) + '.*$\n)+', '', content, flags=re.M).strip()
+        return re.sub(r'(^' + re.escape(comment_marker) + '.*$\n)+', '', content, flags=re.M).strip()
 
-    return value
+    return ''
 
 
 def edit_comment(old_cmt=''):

tests/cmdline/utils/test_multiline.py

@@ -7,11 +7,12 @@
 # For further information on the license, see the LICENSE.txt file        #
 # For further information please visit http://www.aiida.net               #
 ###########################################################################
-# pylint: disable=unused-argument
+# pylint: disable=unused-argument,invalid-name
 """Unit tests for editing pre and post bash scripts, comments, etc."""
+import click
 import pytest
 
-from aiida.cmdline.utils.multi_line_input import edit_comment
+from aiida.cmdline.utils.multi_line_input import edit_comment, edit_multiline_template
 
 COMMAND = 'sleep 1 ; vim -c "g!/^#=/s/$/Test" -cwq'  # Appends `Test` to every line NOT starting with `#=`
 
@@ -27,3 +28,22 @@ def test_edit_comment(non_interactive_editor):
     old_comment = 'OldComment'
     new_comment = edit_comment(old_cmt=old_comment)
     assert new_comment == old_comment + 'Test'
+
+
+@pytest.mark.parametrize('non_interactive_editor', (COMMAND,), indirect=True)
+def test_edit_multiline_template_empty(non_interactive_editor, monkeypatch):
+    """Test ``edit_multiline_template`` returns empty string when `click.edit` returns empty value e.g. ``None``."""
+
+    def edit(*args, **kwargs):
+        return None
+
+    monkeypatch.setattr(click, 'edit', edit)
+
+    assert edit_multiline_template(template_name='multiline.tpl') == ''
+
+
+@pytest.mark.parametrize('non_interactive_editor', (COMMAND,), indirect=True)
+def test_edit_multiline_template(non_interactive_editor):
+    """Test ``edit_multiline_template`` returns empty string when `click.edit` returns empty value e.g. ``None``."""
+    # The template will contain two empty lines, and those will get `Test` appended to it
+    assert edit_multiline_template(template_name='multiline.tpl') == 'Test\nTest'