Subject: Glossary likely to contain redundant terms or needs to be specific for every project.

Problem

• At the moment every defined term in the glossary is included whether there is a matching :term: or not - this means that every project needs to have a unique glossary, or to reference a common glossary without possibly many redundant terms.

Procedure to reproduce the problem

Add to glossary a definition such as:

ZXZXY 
   This is a term that is **never** used in the document!

and make the documents in any format.

Error logs / results

No Errors

• Document contains definition above but no matching :term: entries.

Expected results

I would like the glossary to possibly automatically or via a filter modifier to the :glossary: entry filter on the actual :term: items present in the document being built and only include those terms in the output documents. N.B. may need to recursively check the filtered glossary entries for :term: items not currently included in case of definitions that introduce other terms but possibly this could be done by linking entries that contain terms defined in other entries so if the child is included the parent is automatically.

Ideally I would be able to have a glossary entry in my current project with include directives to the department glossary, (which might have include directives to the company glossary, etc.).

It would also be possible to have a mechanism for using entries from a default glossary into a generated glossary based on searching the project for :term: items and make this a pre-build step but I suspect that this would be less clean - this mechanism could be a possible "contrib" item.

Reproducible project / your project

• This should be able to be caused/found in any project - I suspect that many current projects have glossary entries without matching :term: items due to either over enthusiastic defining or terms being removed over the life of the document.

Environment info

• OS: Any
• Python version: 2.7.x, >3.3
• Sphinx version: 1.5.3
• Other tools: N/A