Fixes microsoft#199251 (microsoft#199510)

Author: hediet

src/vs/workbench/contrib/multiDiffEditor/browser/multiDiffEditorInput.ts

@@ -5,6 +5,7 @@
 
 import { LazyStatefulPromise, raceTimeout } from 'vs/base/common/async';
 import { onUnexpectedError } from 'vs/base/common/errors';
+import { IMarkdownString } from 'vs/base/common/htmlContent';
 import { IDisposable, DisposableStore, toDisposable } from 'vs/base/common/lifecycle';
 import { deepClone } from 'vs/base/common/objects';
 import { isDefined, isObject } from 'vs/base/common/types';
@@ -114,7 +115,12 @@ export class MultiDiffEditorInput extends EditorInput implements ILanguageSuppor
 					modified: r.modifiedRef ? r.modifiedRef.object.textEditorModel : r.modifiedModel!,
 					title: r.title,
 					get options() {
-						return computeOptions(textResourceConfigurationService.getValue(uri));
+						r.modifiedRef?.object.isReadonly;
+
+						return {
+							...getReadonlyConfiguration(r.modifiedRef?.object.isReadonly() ?? true),
+							...computeOptions(textResourceConfigurationService.getValue(uri)),
+						} satisfies IDiffEditorOptions;
 					},
 					onOptionsDidChange: h => this._textResourceConfigurationService.onDidChangeConfiguration(e => {
 						if (e.affectsConfiguration(uri, 'editor') || e.affectsConfiguration(uri, 'diffEditor')) {
@@ -127,6 +133,13 @@ export class MultiDiffEditorInput extends EditorInput implements ILanguageSuppor
 	}
 }
 
+function getReadonlyConfiguration(isReadonly: boolean | IMarkdownString | undefined): { readOnly: boolean; readOnlyMessage: IMarkdownString | undefined } {
+	return {
+		readOnly: !!isReadonly,
+		readOnlyMessage: typeof isReadonly !== 'boolean' ? isReadonly : undefined
+	};
+}
+
 function computeOptions(configuration: IEditorConfiguration): IDiffEditorOptions {
 	const editorConfiguration = deepClone(configuration.editor);