fixed mkdirs sometimes failing due to race condition when multiprocess builds are running

moonbuild/_fs.moon

@@ -166,10 +166,16 @@ mkdir = (dir) ->
 	clearentry parent dir
 
 mkdirs = (dir) ->
-	return if isdir dir
-	error "Can't mkdirs #{dir}: file exists" if exists dir
+	if attr = attributes normalizepath dir
+		return if attr.mode == 'directory'
+		error "Can't mkdirs #{dir}: file exists"
 	mkdirs parent dir
-	mkdir dir
+	unless pcall -> actualmkdir dir
+		clearentry parent dir
+		clearentry dir
+		error "Failed to mkdirs #{dir}: last mkdir failed" unless isdir dir
+	clearentry parent dir
+	clearentry dir
 
 -- from the backend
 fs = {k, withcache fn for k, fn in pairs fs}

out/moonbuild.lua

@@ -973,14 +973,27 @@ mkdir = function(dir)
 end
 local mkdirs
 mkdirs = function(dir)
-  if isdir(dir) then
+  do
+    local attr = attributes(normalizepath(dir))
+    if attr then
+      if attr.mode == 'directory' then
         return 
       end
-  if exists(dir) then
       error("Can't mkdirs " .. tostring(dir) .. ": file exists")
     end
+  end
   mkdirs(parent(dir))
-  return mkdir(dir)
+  if not (pcall(function()
+    return actualmkdir(dir)
+  end)) then
+    clearentry(parent(dir))
+    clearentry(dir)
+    if not (isdir(dir)) then
+      error("Failed to mkdirs " .. tostring(dir) .. ": last mkdir failed")
+    end
+  end
+  clearentry(parent(dir))
+  return clearentry(dir)
 end
 do
   local _tbl_0 = { }