diff --git a/src/vs/editor/common/languages.ts b/src/vs/editor/common/languages.ts
index cd402de4dc4..2cae627b585 100644
--- a/src/vs/editor/common/languages.ts
+++ b/src/vs/editor/common/languages.ts
@@ -1543,7 +1543,7 @@ export interface CommentThread<T = IRange> {
 	label: string | undefined;
 	contextValue: string | undefined;
 	comments: Comment[] | undefined;
-	onDidChangeComments: Event<Comment[] | undefined>;
+	onDidChangeComments: Event<readonly Comment[] | undefined>;
 	collapsibleState?: CommentThreadCollapsibleState;
 	initialCollapsibleState?: CommentThreadCollapsibleState;
 	onDidChangeInitialCollapsibleState: Event<CommentThreadCollapsibleState | undefined>;
diff --git a/src/vs/workbench/api/browser/mainThreadComments.ts b/src/vs/workbench/api/browser/mainThreadComments.ts
index 77fc0e85e72..f417fe688e2 100644
--- a/src/vs/workbench/api/browser/mainThreadComments.ts
+++ b/src/vs/workbench/api/browser/mainThreadComments.ts
@@ -77,8 +77,8 @@ export class MainThreadCommentThread<T> implements languages.CommentThread<T> {
 		this._onDidChangeComments.fire(this._comments);
 	}
 
-	private readonly _onDidChangeComments = new Emitter<languages.Comment[] | undefined>();
-	get onDidChangeComments(): Event<languages.Comment[] | undefined> { return this._onDidChangeComments.event; }
+	private readonly _onDidChangeComments = new Emitter<readonly languages.Comment[] | undefined>();
+	get onDidChangeComments(): Event<readonly languages.Comment[] | undefined> { return this._onDidChangeComments.event; }
 
 	set range(range: T) {
 		this._range = range;
diff --git a/src/vs/workbench/api/browser/mainThreadSCM.ts b/src/vs/workbench/api/browser/mainThreadSCM.ts
index 5ac8c935667..24aec5842d2 100644
--- a/src/vs/workbench/api/browser/mainThreadSCM.ts
+++ b/src/vs/workbench/api/browser/mainThreadSCM.ts
@@ -127,8 +127,8 @@ class MainThreadSCMProvider implements ISCMProvider {
 	private readonly _onDidChangeCommitTemplate = new Emitter<string>();
 	readonly onDidChangeCommitTemplate: Event<string> = this._onDidChangeCommitTemplate.event;
 
-	private readonly _onDidChangeStatusBarCommands = new Emitter<Command[]>();
-	get onDidChangeStatusBarCommands(): Event<Command[]> { return this._onDidChangeStatusBarCommands.event; }
+	private readonly _onDidChangeStatusBarCommands = new Emitter<readonly Command[]>();
+	get onDidChangeStatusBarCommands(): Event<readonly Command[]> { return this._onDidChangeStatusBarCommands.event; }
 
 	private readonly _onDidChange = new Emitter<void>();
 	readonly onDidChange: Event<void> = this._onDidChange.event;
diff --git a/src/vs/workbench/api/common/extHostDiagnostics.ts b/src/vs/workbench/api/common/extHostDiagnostics.ts
index 7376effaf75..8e76e228758 100644
--- a/src/vs/workbench/api/common/extHostDiagnostics.ts
+++ b/src/vs/workbench/api/common/extHostDiagnostics.ts
@@ -21,7 +21,7 @@ import { ExtHostDocumentsAndEditors } from 'vs/workbench/api/common/extHostDocum
 export class DiagnosticCollection implements vscode.DiagnosticCollection {
 
 	readonly #proxy: MainThreadDiagnosticsShape | undefined;
-	readonly #onDidChangeDiagnostics: Emitter<vscode.Uri[]>;
+	readonly #onDidChangeDiagnostics: Emitter<readonly vscode.Uri[]>;
 	readonly #data: ResourceMap<vscode.Diagnostic[]>;
 
 	private _isDisposed = false;
@@ -33,7 +33,7 @@ export class DiagnosticCollection implements vscode.DiagnosticCollection {
 		private readonly _modelVersionIdProvider: (uri: URI) => number | undefined,
 		extUri: IExtUri,
 		proxy: MainThreadDiagnosticsShape | undefined,
-		onDidChangeDiagnostics: Emitter<vscode.Uri[]>
+		onDidChangeDiagnostics: Emitter<readonly vscode.Uri[]>
 	) {
 		this.#data = new ResourceMap(uri => extUri.getComparisonKey(uri));
 		this.#proxy = proxy;
@@ -226,9 +226,9 @@ export class ExtHostDiagnostics implements ExtHostDiagnosticsShape {
 
 	private readonly _proxy: MainThreadDiagnosticsShape;
 	private readonly _collections = new Map<string, DiagnosticCollection>();
-	private readonly _onDidChangeDiagnostics = new DebounceEmitter<vscode.Uri[]>({ merge: all => all.flat(), delay: 50 });
+	private readonly _onDidChangeDiagnostics = new DebounceEmitter<readonly vscode.Uri[]>({ merge: all => all.flat(), delay: 50 });
 
-	static _mapper(last: vscode.Uri[]): { uris: readonly vscode.Uri[] } {
+	static _mapper(last: readonly vscode.Uri[]): { uris: readonly vscode.Uri[] } {
 		const map = new ResourceMap<vscode.Uri>();
 		for (const uri of last) {
 			map.set(uri, uri);
diff --git a/src/vs/workbench/api/common/extHostDocumentsAndEditors.ts b/src/vs/workbench/api/common/extHostDocumentsAndEditors.ts
index 66f2d74c847..bb64f26fa8e 100644
--- a/src/vs/workbench/api/common/extHostDocumentsAndEditors.ts
+++ b/src/vs/workbench/api/common/extHostDocumentsAndEditors.ts
@@ -48,14 +48,14 @@ export class ExtHostDocumentsAndEditors implements ExtHostDocumentsAndEditorsSha
 	private readonly _editors = new Map<string, ExtHostTextEditor>();
 	private readonly _documents = new ResourceMap<Reference<ExtHostDocumentData>>();
 
-	private readonly _onDidAddDocuments = new Emitter<ExtHostDocumentData[]>();
-	private readonly _onDidRemoveDocuments = new Emitter<ExtHostDocumentData[]>();
-	private readonly _onDidChangeVisibleTextEditors = new Emitter<vscode.TextEditor[]>();
+	private readonly _onDidAddDocuments = new Emitter<readonly ExtHostDocumentData[]>();
+	private readonly _onDidRemoveDocuments = new Emitter<readonly ExtHostDocumentData[]>();
+	private readonly _onDidChangeVisibleTextEditors = new Emitter<readonly vscode.TextEditor[]>();
 	private readonly _onDidChangeActiveTextEditor = new Emitter<vscode.TextEditor | undefined>();
 
-	readonly onDidAddDocuments: Event<ExtHostDocumentData[]> = this._onDidAddDocuments.event;
-	readonly onDidRemoveDocuments: Event<ExtHostDocumentData[]> = this._onDidRemoveDocuments.event;
-	readonly onDidChangeVisibleTextEditors: Event<vscode.TextEditor[]> = this._onDidChangeVisibleTextEditors.event;
+	readonly onDidAddDocuments: Event<readonly ExtHostDocumentData[]> = this._onDidAddDocuments.event;
+	readonly onDidRemoveDocuments: Event<readonly ExtHostDocumentData[]> = this._onDidRemoveDocuments.event;
+	readonly onDidChangeVisibleTextEditors: Event<readonly vscode.TextEditor[]> = this._onDidChangeVisibleTextEditors.event;
 	readonly onDidChangeActiveTextEditor: Event<vscode.TextEditor | undefined> = this._onDidChangeActiveTextEditor.event;
 
 	constructor(
diff --git a/src/vs/workbench/api/common/extHostTextEditors.ts b/src/vs/workbench/api/common/extHostTextEditors.ts
index b221ea9710c..7ab8d65df53 100644
--- a/src/vs/workbench/api/common/extHostTextEditors.ts
+++ b/src/vs/workbench/api/common/extHostTextEditors.ts
@@ -20,14 +20,14 @@ export class ExtHostEditors implements ExtHostEditorsShape {
 	private readonly _onDidChangeTextEditorVisibleRanges = new Emitter<vscode.TextEditorVisibleRangesChangeEvent>();
 	private readonly _onDidChangeTextEditorViewColumn = new Emitter<vscode.TextEditorViewColumnChangeEvent>();
 	private readonly _onDidChangeActiveTextEditor = new Emitter<vscode.TextEditor | undefined>();
-	private readonly _onDidChangeVisibleTextEditors = new Emitter<vscode.TextEditor[]>();
+	private readonly _onDidChangeVisibleTextEditors = new Emitter<readonly vscode.TextEditor[]>();
 
 	readonly onDidChangeTextEditorSelection: Event<vscode.TextEditorSelectionChangeEvent> = this._onDidChangeTextEditorSelection.event;
 	readonly onDidChangeTextEditorOptions: Event<vscode.TextEditorOptionsChangeEvent> = this._onDidChangeTextEditorOptions.event;
 	readonly onDidChangeTextEditorVisibleRanges: Event<vscode.TextEditorVisibleRangesChangeEvent> = this._onDidChangeTextEditorVisibleRanges.event;
 	readonly onDidChangeTextEditorViewColumn: Event<vscode.TextEditorViewColumnChangeEvent> = this._onDidChangeTextEditorViewColumn.event;
 	readonly onDidChangeActiveTextEditor: Event<vscode.TextEditor | undefined> = this._onDidChangeActiveTextEditor.event;
-	readonly onDidChangeVisibleTextEditors: Event<vscode.TextEditor[]> = this._onDidChangeVisibleTextEditors.event;
+	readonly onDidChangeVisibleTextEditors: Event<readonly vscode.TextEditor[]> = this._onDidChangeVisibleTextEditors.event;
 
 	private readonly _proxy: MainThreadTextEditorsShape;
 
diff --git a/src/vs/workbench/api/test/browser/extHostDiagnostics.test.ts b/src/vs/workbench/api/test/browser/extHostDiagnostics.test.ts
index aaeb523fbe2..ac429a5255a 100644
--- a/src/vs/workbench/api/test/browser/extHostDiagnostics.test.ts
+++ b/src/vs/workbench/api/test/browser/extHostDiagnostics.test.ts
@@ -299,7 +299,7 @@ suite('ExtHostDiagnostics', () => {
 	});
 
 	test('diagnostic eventing', async function () {
-		const emitter = new Emitter<Array<URI>>();
+		const emitter = new Emitter<readonly URI[]>();
 		const collection = new DiagnosticCollection('ddd', 'test', 100, versionProvider, extUri, new DiagnosticsShape(), emitter);
 
 		const diag1 = new Diagnostic(new Range(1, 1, 2, 3), 'diag1');
@@ -337,7 +337,7 @@ suite('ExtHostDiagnostics', () => {
 	});
 
 	test('vscode.languages.onDidChangeDiagnostics Does Not Provide Document URI #49582', async function () {
-		const emitter = new Emitter<Array<URI>>();
+		const emitter = new Emitter<readonly URI[]>();
 		const collection = new DiagnosticCollection('ddd', 'test', 100, versionProvider, extUri, new DiagnosticsShape(), emitter);
 
 		const diag1 = new Diagnostic(new Range(1, 1, 2, 3), 'diag1');
diff --git a/src/vs/workbench/contrib/scm/common/scm.ts b/src/vs/workbench/contrib/scm/common/scm.ts
index 0629e491de5..a98e8912f51 100644
--- a/src/vs/workbench/contrib/scm/common/scm.ts
+++ b/src/vs/workbench/contrib/scm/common/scm.ts
@@ -63,10 +63,10 @@ export interface ISCMProvider extends IDisposable {
 	readonly count?: number;
 	readonly commitTemplate: string;
 	readonly onDidChangeCommitTemplate: Event<string>;
-	readonly onDidChangeStatusBarCommands?: Event<Command[]>;
+	readonly onDidChangeStatusBarCommands?: Event<readonly Command[]>;
 	readonly acceptInputCommand?: Command;
 	readonly actionButton?: ISCMActionButtonDescriptor;
-	readonly statusBarCommands?: Command[];
+	readonly statusBarCommands?: readonly Command[];
 	readonly onDidChange: Event<void>;
 
 	getOriginalResource(uri: URI): Promise<URI | null>;