defaults(fix): purge entry from persistent file

frontend/apps/filemanager/filemanagersetdefaults.lua

@@ -291,12 +291,23 @@ function SetDefaults:SaveSettings()
         if not self.changed[j] then checked[j] = true end
     end
 
-    -- handle case "found in persistent" and changed, replace it
+    -- load default value for defaults
+    local defaults = {}
+    local load_defaults = loadfile(defaults_path)
+    setfenv(load_defaults, defaults)
+    load_defaults()
+    -- handle case "found in persistent" and changed, replace/delete it
     for k, v in pairs(persisted_defaults) do
         for j=1, #self.defaults_name do
             if not checked[j]
             and k == self.defaults_name[j] then
-                persisted_defaults[k] = self.defaults_value[j]
+                -- remove from persist if value got reverted back to the
+                -- default one
+                if defaults[k] == self.defaults_value[j] then
+                    persisted_defaults[k] = nil
+                else
+                    persisted_defaults[k] = self.defaults_value[j]
+                end
                 checked[j] = true
             end
         end

spec/unit/defaults_spec.lua

@@ -82,6 +82,45 @@ DCREREADER_CONFIG_MARGIN_SIZES_LARGE = {
     [4] = 20
 }
 DCREREADER_VIEW_MODE = "page"
+]],
+                       fd:read("*a"))
+        fd:close()
+        os.remove(persistent_filename)
+    end)
+
+    it("should delete entry from defaults.persistent.lua if value is reverted back to default", function()
+        local persistent_filename = DataStorage:getDataDir() .. "/defaults.persistent.lua"
+        local fd = io.open(persistent_filename, "w")
+        fd:write(
+[[-- For configuration changes that persists between updates
+SEARCH_TITLE = true
+DCREREADER_CONFIG_MARGIN_SIZES_LARGE = {
+    [1] = 20,
+    [2] = 20,
+    [3] = 20,
+    [4] = 20
+}
+DCREREADER_VIEW_MODE = "page"
+DHINTCOUNT = 2
+]])
+        fd:close()
+
+        -- in persistent
+        Defaults:init()
+        Defaults.changed[29] = true
+        Defaults.defaults_value[29] = 1
+        Defaults:SaveSettings()
+        fd = io.open(persistent_filename)
+        assert.Equals(
+[[-- For configuration changes that persists between updates
+SEARCH_TITLE = true
+DCREREADER_VIEW_MODE = "page"
+DCREREADER_CONFIG_MARGIN_SIZES_LARGE = {
+    [1] = 20,
+    [2] = 20,
+    [3] = 20,
+    [4] = 20
+}
 ]],
                        fd:read("*a"))
         fd:close()