hs.ipc: Avoid reentrance when in printReplacement

extensions/ipc/ipc.lua

@@ -33,19 +33,54 @@ local MSG_ID = {
     CONSOLE    =  3,    -- cloned console output
 }
 
+-- stop printReplacement from being reentrant
+-- otherwise errors might cascade into lots of recursive prints
+-- hammerspoon is single threaded, thus this does not need a semaphore
+-- otherwise we'll have to deal with a potential race condition
+module.insidePrintInstances = {}
+
+module.print_enter = function(instance)
+  val = module.insidePrintInstances[instance] or 0
+  module.insidePrintInstances[instance] = val + 1
+end
+
+module.print_exit = function(instance)
+  -- make sure instance exists
+  if module.insidePrintInstances[instance] then
+    module.insidePrintInstances[instance] = module.insidePrintInstances[instance] - 1
+    -- make sure to delete the entry from the table to avoid
+    -- growing forever
+    if module.insidePrintInstances[instance] == 0 then
+      module.insidePrintInstances[instance] = nil
+    end
+  end
+end
+
+module.print_inside = function(instance)
+  -- return true if we are already inside printReplacement
+  val = module.insidePrintInstances[instance]
+  return val and val > 0
+end
+
 local originalPrint = print
 local printReplacement = function(...)
     originalPrint(...)
-    for _,v in pairs(module.__registeredCLIInstances) do
+    for id,v in pairs(module.__registeredCLIInstances) do
         if v._cli.console and v.print and not v._cli.quietMode then
---            v.print(...)
--- make it more obvious what is console output versus the command line's
+          if module.print_inside(id) then
+            log.w(string.format("Instance of [%s] already recursing, refusing request.", id))
+          else
+            module.print_enter(id)
+            --            v.print(...)
+            -- make it more obvious what is console output versus the command line's
             local things = table.pack(...)
             local stdout = (things.n > 0) and tostring(things[1]) or ""
             for i = 2, things.n do
-                stdout = stdout .. "\t" .. tostring(things[i])
+              stdout = stdout .. "\t" .. tostring(things[i])
             end
             v._cli.remote:sendMessage(stdout .. "\n", MSG_ID.CONSOLE)
+            module.print_exit(id)
+          end
         end
     end
 end