def visit_DEDENT(self, node: Leaf) -> Iterator[Line]:
        """Decrease indentation level, maybe yield a line."""
        # The current line might still wait for trailing comments.  At DEDENT time
        # there won't be any (they would be prefixes on the preceding NEWLINE).
        # Emit the line then.
        yield from self.line()

        # While DEDENT has no value, its prefix may contain standalone comments
        # that belong to the current indentation level.  Get 'em.
        yield from self.visit_default(node)

        # Finally, emit the dedent.
        yield from self.line(-1)
Decrease indentation level, maybe yield a line.
src/black/linegen.py