[jhoechtl]

> Or, even more annoyingly, I've just got an interface and no clue about where to find the implementation.

That bites me often times. Does gopls help in this regard? Can any tool besides the compiler help me to answer, what methods in a particular piece of code implement what interface?

[Nullabillity]

Not even the compiler knows, since interfaces are resolved at runtime. You could build a list of potential implementations, but then structural typing means that it can't know the difference between an intentional and accidental implementation.