Retrieve a list of files passed down by parent theme(s)

[chrispytoes]

I am building a theme that searches for component files with my own naming syntax. I want these special component files to override from one theme to the next. For some of these component files, there will be default fallbacks in my base theme, but most will be created by the theme user. So If I simply search my own theme's directory structure, that wouldn't include the theme files passed down by the parent project/theme.

I need a way to locate my component template files in each parent theme going up, so I can interpret them with my naming syntax, while also allowing overrides and fallbacks from one theme to the next.

I have two ideas on how I can potentially do this, so I'm just looking for some confirmation on what is best/possible.

1. Somehow reliably find the location of the root project, as well as all ancestor themes in between. I can then just do all the override logic myself to find and consume the template files my theme is searching for.
2. If it's possible to retrieve the list of files resulting from Gatsby's file override mechanism, this would be perfect. Does Gatsby make a prebuilt list of all the files passed down by parent themes that I can get? Or does it simply go directly to the files it needs as it builds?