Perform auto whitespace trimming before explicit saving (close #1444)

CHANGELOG.md

@@ -20,6 +20,7 @@ Change Log
 - Update the character inspector to add labels for each item and display the Unicode version.
 - Deprecate the print font setting in the Print settings.
 - Deprecate the cursor type option.
+- Make sure to perform the automatic whitespace trimming every time before explicit saving by the user.
 - Migrate the sharing interface to the modern version.
 - [trivial] Migrate the Opacity toolbar item to popover in macOS 14.
 - [trivial] Disable the contextual menu for shortcut fields.

CotEditor/Sources/Document.swift

@@ -418,9 +418,17 @@ final class Document: NSDocument, AdditionalDocumentPreparing, EncodingHolder {
     
     override func save(to url: URL, ofType typeName: String, for saveOperation: NSDocument.SaveOperationType, completionHandler: @escaping ((any Error)?) -> Void) {
         
+        assert(Thread.isMainThread)
+        
         // break undo grouping
-        for layoutManager in self.textStorage.layoutManagers {
-            layoutManager.textViewForBeginningOfSelection?.breakUndoCoalescing()
+        let textViews = self.textStorage.layoutManagers.compactMap(\.textViewForBeginningOfSelection)
+        for textView in textViews {
+            textView.breakUndoCoalescing()
+        }
+        
+        // trim trailing whitespace if needed
+        if !saveOperation.isAutosave, UserDefaults.standard[.autoTrimsTrailingWhitespace] {
+            textViews.first?.trimTrailingWhitespace(ignoresEmptyLines: !UserDefaults.standard[.trimsWhitespaceOnlyLines])
         }
         
         // workaround the issue that invoking the async version super blocks the save process