How can I watch variables when debugging Vimscript?

Question

I would like to have another pane active when debugging a Vimscript function which would show the values of chosen local variables and function arguments dynamically.

Currently I have to echo or let to see variable values. It would be more convenient to have them display automatically.

Is there a way to do this without a plugin? Is there an easy way to script this with, say, an autocommand for example?

Answer 1

Vim :debug sessions are modal. When started we are prisoner of this non ergonomic mode. We could try to send anything we want to a buffer or a window, that window will never get refreshed and properly displayed. I guess Vim core would need to be multithreaded to support this, which is not the case. This _issue_ was quickly mentioned during a poll on what plugin authors would need.

There is no native way to watch variables while debugging a vim script. There exist plugins though. I'm aware of https://github.com/albfan/vim-breakpts -- which, IIRC, runs another vim session where the script being debugged is actually ran.

Because of the poor native user interface of :debug I do my best to avoid loops (I use map(), filter()... instead), and I often try to avoid debugging and instead play with with a few frameworks I'm maintaining:

• a logging framework
• a unit-testing framework
• a DbC framework -- actually on failed assertions, I often end-up in debug mode.

Since my initial answer, I've documented my take regarding debugging in my plugins.

Answer 2

Even in v8.1, the short answer is no; you cannot positional-statically display the content of a variable without a plugin ... OR additional vim scripting.

Alternatively

However, Decho plugin does allow you to write info into another screen/buffer in a live manner using function calls.

And DBGp is a debugger GUI for Vim debugging session (written in Python and Vimscript) also will write variable values to another "window" pane (or grid box) in a static cursor positional manner.

Both of which you could extract certain Vim script codings that deals with placing variable values in another actively-displayed buffer, in which you could put these snippet of codes into your local ~/.vimrc and that would be the solution for your 'plugin-less' approach.

References

• Decho (by Dr.Chip) or
• or this updated Vim debugger (DBGp) plugin in Github.