fix: return empty response to textDocument/formatting if no changes

Do not send "edits" if the content remains unchanged after LSP
formatting. Otherwise, Neovim reports an unsaved buffer even when no
actual changes were made

Author: danielleontiev

changelog.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 <!-- Add all new changes here. They will be moved under a version at release -->
+* `FIX` prevent unnecessary edits by LSP formatting when content did not change
 
 ## 3.13.9
 `2025-3-13`

script/core/formatting.lua

@@ -21,6 +21,10 @@ return function(uri, options)
         return
     end
 
+    if text == formattedText then
+        return
+    end
+
     return {
         {
             start = state.ast.start,