A while back, I had someone here help me craft a custom mu-plugin (aka: "must use" plugin) that was designed to specially handle 404 server responses. Here is that thread for context, complete with the specific code I'm referencing:
Question about repurposing WordPress 404 handler
I'm just now revisiting this project and trying to resume development on it, but am running in to some issues with using the "get_template_part" method within the mu-plugin file .. trying to pull in specific PHP template files that are part of my child theme. It doesn't seem to be working, however, and I'm wondering if either it isn't possible, -- OR -- if there might be something obvious or essential that I'm missing.
I know that I'm able to reference methods such as get_header() and get_footer() without any issues in the mu-plugin file, so I don't think I need to load the entire WP core in order to be able to use get_template_part. I've also tried to use "include" and "require" instead of "get_template_part", and that didn't work either. This leads me to suspect that I might need to set some kind of "base path" or something, though I'm not entirely sure how I might go about that.
The reason I'm eager to get this all working, by the way, is because I've already done a significant amount of custom programming within my child theme, and all of the code that I'm trying to pull in and render to the browser using the mu-plugin currently lives within that child theme. Having to duplicate all of that code within my mu-plugin file certainly wouldn't be ideal, and would likely be more difficult to maintain moving forward. So .. hopefully I can find some kind of solution to this. Please advise.
