[rosdoc2] Fix document generation on buildfarm (#701)

* Update system path and fix dep

Signed-off-by: Yadunund <yadunund@gmail.com>

* Add lark to doc_depend

Signed-off-by: Yadunund <yadunund@gmail.com>

---------

Signed-off-by: Yadunund <yadunund@gmail.com>

Author: Yadunund

launch/doc/source/conf.py

@@ -35,7 +35,7 @@
 # with the same name of this package within the docs_build directory.
 # Hence we add the parent folder to the system path so that the modules from
 # this package can be imported.
-sys.path.insert(0, os.path.abspath('..'))
+sys.path.insert(0, os.path.abspath('.'))
 
 
 # -- Project information -----------------------------------------------------

launch/package.xml

@@ -17,6 +17,11 @@
 
   <depend>osrf_pycommon</depend>
 
+  <!-- The rosdep key for python3 lark module is python3-lark-parser.
+  rosdoc2 will mock "lark-parser" however the module is imported as "lark".
+  Hence, to mock the import of the lark module, we add this doc depend. -->
+  <doc_depend>lark</doc_depend>
+
   <exec_depend>ament_index_python</exec_depend>
   <exec_depend>python3-importlib-metadata</exec_depend>
   <exec_depend>python3-lark-parser</exec_depend>