Came up in Discord, I'm personally not too happy with the current resolve implementation that overwrites the function and has to store the state.

For this 3 choices were layed out:

1. Keep the current system that just works™️, simple (as in you don't need to pass other variables), can workaround the init/not init by using . vs ..

2. Add parameters to require that take the current modpath and actual path:

local modpath, path = ...
require("thing", modpath, path) -- also:
require("thing", ...)

3. Add helper functions that allow the user to calculate the modpath:

local common = require "core.common"
require(common.relmod("thing", ...))

with me later proposing a 4th:

4. searcher that walks the stack back and derives the relative modname by inspecting the stack

local searcher0 = package.searchers[2]
table.insert(package.searchers, 1, function(modname)
  if modname:sub(1,1) ~= "." then return nil end

  local _, parent = debug.getlocal(3, -1)
  local _, path = debug.getlocal(3, -2)

  if parent == nil or path == nil then return nil end

  -- Check if we imported a module or a file
  if path:match("init.lua$") == nil then
    parent = parent:match("(.-)%.[^%.]+$")
  end
  modname = parent .. modname

  return searcher0(modname)
end )

(incomplete implementation, but shows you roughly how it would work. Far more efficient when written in C)