naughty: Improve backward compatibility to protecting the constants.

If the user copy/pasted `naughty.config.*` into their config rather
than set values 1 by 1, we could no longer add new values since they
would get removed. To prevent more users being affected by this, we
now silently ignore the new table while still setting all the values.

Fix #3145

lib/naughty/constants.lua

@@ -9,9 +9,10 @@
 -- @copyright 2017 Emmanuel Lepage Vallee
 ----------------------------------------------------------------------------
 local beautiful = require("beautiful")
+local gtable = require("gears.table")
 local dpi = beautiful.xresources.apply_dpi
 
-local ret = {}
+local ret, no_clear = {}, {}
 
 ret.config = {
     padding         = dpi(4),
@@ -21,7 +22,7 @@ ret.config = {
     notify_callback = nil,
 }
 
-ret.config.presets = {
+no_clear.presets = {
     low = {
         timeout = 5
     },
@@ -55,15 +56,15 @@ ret.config._urgency = {
 }
 
 ret.config.mapping = {
-    {{urgency = ret.config._urgency.low     }, ret.config.presets.low}, --compat
-    {{urgency = ret.config._urgency.normal  }, ret.config.presets.normal}, --compat
-    {{urgency = ret.config._urgency.critical}, ret.config.presets.critical}, --compat
-    {{urgency = "low"     }, ret.config.presets.low},
-    {{urgency = "normal"  }, ret.config.presets.normal},
-    {{urgency = "critical"}, ret.config.presets.critical},
+    {{urgency = ret.config._urgency.low     }, no_clear.presets.low}, --compat
+    {{urgency = ret.config._urgency.normal  }, no_clear.presets.normal}, --compat
+    {{urgency = ret.config._urgency.critical}, no_clear.presets.critical}, --compat
+    {{urgency = "low"     }, no_clear.presets.low},
+    {{urgency = "normal"  }, no_clear.presets.normal},
+    {{urgency = "critical"}, no_clear.presets.critical},
 }
 
-ret.config.defaults = {
+no_clear.defaults = {
     timeout      = 5,
     text         = "",
     screen       = nil,
@@ -92,4 +93,21 @@ ret.notification_closed_reason = {
 -- Legacy --TODO v5 remove this alias
 ret.notificationClosedReason = ret.notification_closed_reason
 
+-- `no_clear` is used to prevent users from setting the entire table.
+-- If they did and we added a new default value, then it would not be
+-- backward compatible. For safety, we just crush the tables rather than
+-- replace them.
+setmetatable(ret.config, {
+    __index = function(_, key)
+        return no_clear[key]
+    end,
+    __newindex = function(_, key, value)
+        if no_clear[key] then
+            gtable.crush(no_clear[key], value)
+        else
+            rawset(ret.config, key, value)
+        end
+    end
+})
+
 return ret

tests/test-naughty-legacy.lua

@@ -1256,4 +1256,15 @@ table.insert(steps, function()
     return true
 end)
 
+-- Make sure it isn't possible to remove default variables (#3145).
+table.insert(steps, function()
+    naughty.config.defaults = {fake_variable = 24}
+    naughty.config.text = 1337
+    assert(naughty.config.defaults.fake_variable == 24)
+    assert(naughty.config.defaults.timeout == 5)
+    assert(naughty.config.text == 1337)
+
+     return true
+end)
+
 require("_runner").run_steps(steps)