[Doc] Gluon Block/HybridBlock/SymbolBlock appears at the wrong place in the API doc

[icemelon]

Description

Gluon Block, HybridBlock, SymbolBlock has an empty doc in the API doc. For example: https://mxnet.apache.org/api/python/docs/api/gluon/block.html

Their actual docs appear under gluon.nn domain, which IMO is a wrong place for them. For example: https://mxnet.apache.org/api/python/docs/api/gluon/nn/index.html#mxnet.gluon.nn.Block

@ys2843

[leezu]

I notice that 1.6 site displays both locations

https://mxnet.apache.org/versions/1.6/api/python/docs/api/gluon/block.html#mxnet.gluon.Block
https://mxnet.apache.org/versions/1.6/api/python/docs/api/gluon/nn/index.html#mxnet.gluon.nn.Block

Maybe Sphinx get's interrupted during generating the gluon/block.html page because it contains some files with broken links:
For example, the following file refers to API that has been removed https://github.com/apache/incubator-mxnet/blob/243ade93bcb8b7962d1faeb89c98409e3ae0d7a4/docs/python_docs/python/api/gluon/parameter_dict.rst

Deleting this file may be sufficient for fixing the site

@ys2843 can you please help make sure the broken link checker runs on every PR to avoid such issues going forward? Maybe activating the warning-is-error in https://github.com/apache/incubator-mxnet/blob/243ade93bcb8b7962d1faeb89c98409e3ae0d7a4/docs/python_docs/python/scripts/conf.py or changing a different option would be sufficient?

[sandeep-krishnamurthy]

@leezu - Should we revert the PR ( #18413 ) if we are unable to fix the broken website issue quickly. Ideally this should have been caught before the PR was merged. We shall work on it as you suggested above to have broken link checker as part of the PR build. But, given currently Python APIs are broken, I prefer we revert and merge back with the fix.
What do you think?

[leezu]

I suggest we focus on ensuring our users see the stable API docs, given that most users don't use MXNet 2 at this point anyways. This PR has exposed some bugs in the Sphinx setup which need to be fixed before the release; but this is an issue with the website generation script and shouldn't delay the feature development. What do you think @sandeep-krishnamurthy

[leezu]

WARNING: autodoc: failed to import module 'executor' from module 'mxnet'; the following exception was raised:
No module named 'scipy'
from the log

b4b8b80 introduces the scipy import