Add old_text to TextArea widget text change callback

docs/dev/Lua API.rst

@@ -5555,7 +5555,7 @@ TextArea Attributes:
     Functions similarly to the ``ignore_keys`` attribute in the ``EditField`` class.
 
 * ``on_text_change``: Callback function called whenever the text changes.
-    The function signature should be ``on_text_change(new_text)``.
+    The function signature should be ``on_text_change(new_text, old_text)``.
 
 * ``on_cursor_change``: Callback function called whenever the cursor position changes.
     Expected function signature is ``on_cursor_change(new_cursor, old_cursor)``.

library/lua/gui/widgets/text_area.lua

@@ -34,10 +34,10 @@ function TextArea:init()
         debug=self.debug,
         one_line_mode=self.one_line_mode,
 
-        on_text_change=function (val)
+        on_text_change=function (text, old_text)
             self:updateLayout()
             if self.on_text_change then
-                self.on_text_change(val)
+                self.on_text_change(text, old_text)
             end
         end,
         on_cursor_change=self:callback('onCursorChange')

library/lua/gui/widgets/text_area/text_area_content.lua

@@ -189,13 +189,14 @@ function TextAreaContent:paste()
 end
 
 function TextAreaContent:setText(text)
-    local changed = self.text ~= text
+    local old_text = self.text
+
     self.text = self:normalizeText(text)
 
     self:recomputeLines()
 
-    if changed and self.on_text_change then
-        self.on_text_change(text)
+    if self.on_text_change and text ~= old_text then
+        self.on_text_change(text, old_text)
     end
 end