ytdl_hook.lua: make exec return a single value

This refactors exec to only return the result of the subprocess command,
and makes the rest of run_ytdl_hook use the fields of this result,
because specifying all those return values multiple times is unwieldy
now that exec is called several times, and this is easier to read
anyway.

I removed the line
err = string.format("%s returned '%d'", err, es)
altogether instead of updating the es variable, because there was no
chance of it being executed since it would only happen when
result.killed_by_us is true, but run_ytdl_hook returns early when it is.

player/lua/ytdl_hook.lua

@@ -96,11 +96,12 @@ end
 local function exec(args)
     msg.debug("Running: " .. table.concat(args, " "))
 
-    local ret = mp.command_native({name = "subprocess",
+    return mp.command_native({
-                                   args = args,
+        name = "subprocess",
-                                   capture_stdout = true,
+        args = args,
-                                   capture_stderr = true})
+        capture_stdout = true,
-    return ret.status, ret.stdout, ret, ret.killed_by_us
+        capture_stderr = true,
+    })
 end
 
 -- return true if it was explicitly set on the command line
@@ -805,9 +806,9 @@ function run_ytdl_hook(url)
     table.insert(command, "--")
     table.insert(command, url)
 
-    local es, json, result, aborted
+    local result
     if ytdl.searched then
-        es, json, result, aborted = exec(command)
+        result = exec(command)
     else
         local separator = platform_is_windows() and ";" or ":"
         if o.ytdl_path:match("[^" .. separator .. "]") then
@@ -825,12 +826,12 @@ function run_ytdl_hook(url)
                 msg.verbose("Found youtube-dl at: " .. ytdl_cmd)
                 ytdl.path = ytdl_cmd
                 command[1] = ytdl.path
-                es, json, result, aborted = exec(command)
+                result = exec(command)
                 break
             else
                 msg.verbose("No youtube-dl found with path " .. path .. exesuf .. " in config directories")
                 command[1] = path
-                es, json, result, aborted = exec(command)
+                result = exec(command)
                 if result.error_string == "init" then
                     msg.verbose("youtube-dl with path " .. path .. exesuf .. " not found in PATH or not enough permissions")
                 else
@@ -844,20 +845,21 @@ function run_ytdl_hook(url)
         ytdl.searched = true
     end
 
-    if aborted then
+    if result.killed_by_us then
         return
     end
 
+    local json = result.stdout
     local parse_err = nil
 
-    if (es ~= 0) or (json == "") then
+    if result.status ~= 0 or json == "" then
         json = nil
     elseif json then
         json, parse_err = utils.parse_json(json)
     end
 
     if (json == nil) then
-        msg.verbose("status:", es)
+        msg.verbose("status:", result.status)
         msg.verbose("reason:", result.error_string)
         msg.verbose("stdout:", result.stdout)
         msg.verbose("stderr:", result.stderr)
@@ -870,10 +872,8 @@ function run_ytdl_hook(url)
             err = err .. "not found or not enough permissions"
         elseif parse_err then
             err = err .. "failed to parse JSON data: " .. parse_err
-        elseif not result.killed_by_us then
-            err = err .. "unexpected error occurred"
         else
-            err = string.format("%s returned '%d'", err, es)
+            err = err .. "unexpected error occurred"
         end
         msg.error(err)
         if parse_err or string.find(ytdl_err, "yt%-dl%.org/bug") then