Show deprecation warning for viewcode_import

CHANGES

@@ -20,6 +20,7 @@ Bugs fixed
 * deprecation warnings are not emitted
 
   - sphinx.application.CONFIG_FILENAME
+  - :confval:`viewcode_import`
 
 Testing
 --------

sphinx/ext/viewcode.py

@@ -251,6 +251,7 @@ def setup(app):
     app.add_config_value('viewcode_import', None, False)
     app.add_config_value('viewcode_enable_epub', False, False)
     app.add_config_value('viewcode_follow_imported_members', True, False)
+    app.connect('config-inited', migrate_viewcode_import)
     app.connect('doctree-read', doctree_read)
     app.connect('env-merge-info', env_merge_info)
     app.connect('html-collect-pages', collect_pages)