fix(multithreading): support new lane:join() API

Author: Aire-One

src/luacheck/multithreading.lua

@@ -1,3 +1,7 @@
+-- luacheck: push compat
+local unpack = table.unpack or unpack
+-- luacheck: pop
+
 local utils = require "luacheck.utils"
 
 local multithreading = {}
@@ -90,7 +94,20 @@ function multithreading.pmap(func, array, jobs)
    local results = {}
 
    for _, worker in ipairs(workers) do
-      local _, ok, worker_results = assert(worker:join())
+      local join_results = {worker:join()}
+
+      -- Manage both new and old lane:join() API formats.
+      -- See https://github.com/LuaLanes/lanes/commit/bfdc7a92c4e3e99522abb6d90ef2cbb021f36fc8
+      local ok, worker_results, _
+      if #join_results == 4 then
+         -- New API: {true, _, ok, worker_results}
+         _, _, ok, worker_results = unpack(join_results)
+      elseif #join_results == 3 then
+         -- Old API: {true, ok, worker_results}
+         _, ok, worker_results = unpack(join_results)
+      else
+         error("Unexpected lane:join() return format", 0)
+      end
 
       if ok then
          utils.update(results, worker_results)