[avg_dev]

How does one go about implementing something like this? I am quite curious.

[yalue]

Judging by the project, it's implemented by instrumenting the source code; either manually modifying error returns with a wrapper function, or by running source files through an automated tool that will find and modify the return statements for you.

[marhee]

I suspect it is based on https://pkg.go.dev/runtime#Caller