[mdir] Switch to async call

mdir is only semi-tested that it does work:
I have not set up maildir to check if the matching patterns are correct

Changes.md

@@ -16,7 +16,7 @@ Added:
 
 Fixed:
 
-- [volume,gmail,battery(FreeBSD)] Deprecate `io.popen`
+- [volume,gmail,bat_freebsd,mem_freebsd,net_freebsd,mdir] Deprecate `io.popen`
 - [mpd] Lua 5.3 compatibility (for real this time); also correct a typo
 - [pkg,weather,contrib/btc] Allow function call without Awesome
 - [pkg] Use more updated front-ends for Debian/Ubuntu (apt) and Fedora (dnf)

widgets/mdir_all.lua

@@ -5,9 +5,10 @@
 ---------------------------------------------------
 
 -- {{{ Grab environment
-local io = { popen = io.popen }
-local setmetatable = setmetatable
-local helpers = require("vicious.helpers")
+local type = type
+
+local helpers = require"vicious.helpers"
+local spawn = require"vicious.spawn"
 -- }}}
 
 
@@ -17,27 +18,25 @@ local mdir_all = {}
 
 
 -- {{{ Maildir widget type
-local function worker(format, warg)
-    if not warg then return end
-
-    -- Initialize counters
-    local count = { new = 0, cur = 0 }
-
-    for i=1, #warg do
-        quoted_path = helpers.shellquote(warg[i])
-        -- Recursively find new messages
-        local f = io.popen("find "..quoted_path.." -type f -wholename '*/new/*'")
-        for line in f:lines() do count.new = count.new + 1 end
-        f:close()
-
-        -- Recursively find "old" messages lacking the Seen flag
-        local f = io.popen("find "..quoted_path.." -type f -regex '.*/cur/.*2,[^S]*$'")
-        for line in f:lines() do count.cur = count.cur + 1 end
-        f:close()
+function mdir_all.async(format, warg, callback)
+    if type(warg) ~= "table" then return callback{} end
+    local starting_points = ""
+    for i,dir in ipairs(warg) do
+        starting_points = starting_points .. " " .. helpers.shellquote(dir)
     end
+    if starting_points == "" then return callback{ 0, 0 } end
 
-    return {count.new, count.cur}
+    local new, cur = 0, 0
+    spawn.with_line_callback(
+        "find" .. starting_points .. " -type f -regex '.*/cur/.*2,[^S]*$';",
+        { stdout = function (filename) cur = cur + 1 end,
+          output_done = function ()
+              spawn.with_line_callback(
+                  "find" .. starting_points .. " -type f -path '*/new/*';",
+                  { stdout = function (filename) new = new + 1 end,
+                    output_done = function () callback{ new, cur } end })
+          end })
 end
 -- }}}
 
-return setmetatable(mdir_all, { __call = function(_, ...) return worker(...) end })
+return helpers.setasyncall(mdir_all)