A new tool to investigate a tags file

[AmaiKinono]

Discussed in #47

^{Originally posted by AmaiKinono January 23, 2021}
When solving #46, I found that "xref prompts you for an identifier" is a basic tool for investigating a tags file (hence investigating the project that's tagged).

I want a more powerful tool for that. Here's what's in my mind now. After picking a tags file, it prompts you for input. You type:

psd input:scipy#kind:function kind:method

then, it asks readtags to search for tags that has psd in the name, and scipy in the input field. Then, further filtering is done on the elisp side, to pick tags whose kind is function or method.

The input scheme can be designed to be simpler, but the point is two-stage filtering. Before the #, the filter is done by readtags (asynchronously); after the #, it's done by elisp. This 2nd stage part may also be brought to citre-peek to further narrow down the results.

The tags that are filtered out are updated as you input. At any time, you can copy the name of a tag (to paste in your code), jump to its location, or convert those tags into a peek or xref session.

consult and embark are the packages to study. Consult is based on a completing-read wrapper, and has a similar UI for grep (it's asynchronous!). Embark support multiple actions in a completing-read session. Emacs doesn't come with similar functionalities, and it's not easy to implement. So at the end I may develop a separate package based on them and Citre.