diff --git a/.eslint-plugin-local/code-no-redundant-has-before-delete.ts b/.eslint-plugin-local/code-no-redundant-has-before-delete.ts
new file mode 100644
index 00000000000..a13671f4217
--- /dev/null
+++ b/.eslint-plugin-local/code-no-redundant-has-before-delete.ts
@@ -0,0 +1,140 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import * as eslint from 'eslint';
+import type * as ESTree from 'estree';
+import { TSESTree } from '@typescript-eslint/utils';
+
+export default new class NoRedundantHasBeforeDelete implements eslint.Rule.RuleModule {
+
+	readonly meta: eslint.Rule.RuleMetaData = {
+		messages: {
+			noRedundantHasBeforeDelete: 'Do not check for existence before deleting. Map.delete/Set.delete returns a boolean indicating if the element was present.',
+		},
+		fixable: 'code',
+		schema: false,
+	};
+
+	create(context: eslint.Rule.RuleContext): eslint.Rule.RuleListener {
+
+		return {
+			IfStatement(node: any) {
+				const ifStatement = node as TSESTree.IfStatement;
+				const test = ifStatement.test;
+				const consequent = ifStatement.consequent;
+				const hasElse = ifStatement.alternate !== null && ifStatement.alternate !== undefined;
+
+				// Check if the test is a .has() call
+				if (test.type !== 'CallExpression' ||
+					test.callee.type !== 'MemberExpression' ||
+					test.callee.property.type !== 'Identifier' ||
+					test.callee.property.name !== 'has' ||
+					test.arguments.length !== 1) {
+					return;
+				}
+
+				const hasCall = test;
+				const hasCollection = hasCall.callee.object;
+				const hasKey = hasCall.arguments[0];
+
+				// Get the first statement from the consequent
+				let deleteStatement: TSESTree.ExpressionStatement | undefined;
+				if (consequent.type === 'BlockStatement') {
+					if (consequent.body.length === 0) {
+						return;
+					}
+					const firstStatement = consequent.body[0];
+					if (firstStatement.type !== 'ExpressionStatement') {
+						return;
+					}
+					deleteStatement = firstStatement;
+				} else if (consequent.type === 'ExpressionStatement') {
+					deleteStatement = consequent;
+				} else {
+					return;
+				}
+
+				// Check if the first statement is a .delete() call
+				const expr = deleteStatement.expression;
+				if (expr.type !== 'CallExpression' ||
+					expr.callee.type !== 'MemberExpression' ||
+					expr.callee.property.type !== 'Identifier' ||
+					expr.callee.property.name !== 'delete' ||
+					expr.arguments.length !== 1) {
+					return;
+				}
+
+				const deleteCall = expr;
+				const deleteCollection = deleteCall.callee.object;
+				const deleteKey = deleteCall.arguments[0];
+
+				// Compare collection and key using source text
+				const sourceCode = context.sourceCode;
+				const toNode = (n: TSESTree.Node) => n as unknown as ESTree.Node;
+				if (sourceCode.getText(toNode(hasCollection)) !== sourceCode.getText(toNode(deleteCollection)) ||
+					sourceCode.getText(toNode(hasKey)) !== sourceCode.getText(toNode(deleteKey))) {
+					return;
+				}
+
+				context.report({
+					node: ifStatement,
+					messageId: 'noRedundantHasBeforeDelete',
+					fix(fixer) {
+						const deleteCallText = sourceCode.getText(toNode(deleteCall));
+						const ifNode = toNode(ifStatement);
+						const isOnlyDelete = consequent.type === 'ExpressionStatement' ||
+							(consequent.type === 'BlockStatement' && consequent.body.length === 1);
+
+						// Helper to get the range including trailing whitespace
+						const getDeleteRangeWithWhitespace = () => {
+							const deleteNode = toNode(deleteStatement!);
+							const [start, end] = deleteNode.range!;
+							const nextToken = sourceCode.getTokenAfter(deleteNode);
+							if (nextToken && nextToken.range![0] > end) {
+								const textBetween = sourceCode.text.substring(end, nextToken.range![0]);
+								if (textBetween.trim() === '') {
+									return [start, nextToken.range![0]] as [number, number];
+								}
+							}
+							return [start, end] as [number, number];
+						};
+
+						// Case 1: Has else clause
+						if (hasElse) {
+							const elseText = sourceCode.getText(toNode(ifStatement.alternate!));
+
+							if (isOnlyDelete) {
+								// Only delete in consequent: negate and use else
+								// if (m.has(key)) m.delete(key); else ... → if (!m.delete(key)) ...
+								return fixer.replaceText(ifNode, `if (!${deleteCallText}) ${elseText}`);
+							} else {
+								// Multiple statements: replace test and remove delete statement
+								// if (m.has(key)) { m.delete(key); other(); } else ... → if (m.delete(key)) { other(); } else ...
+								return [
+									fixer.replaceTextRange(hasCall.range!, deleteCallText),
+									fixer.removeRange(getDeleteRangeWithWhitespace())
+								];
+							}
+						}
+
+						// Case 2: No else clause
+						if (isOnlyDelete) {
+							// Replace entire if with just the delete call
+							// if (m.has(key)) m.delete(key); → m.delete(key);
+							return fixer.replaceText(ifNode, deleteCallText + ';');
+						} else {
+							// Multiple statements: replace test and remove delete statement
+							// if (m.has(key)) { m.delete(key); other(); } → if (m.delete(key)) { other(); }
+							return [
+								fixer.replaceTextRange(hasCall.range!, deleteCallText),
+								fixer.removeRange(getDeleteRangeWithWhitespace())
+							];
+						}
+					}
+				});
+			}
+		};
+	}
+};
diff --git a/.eslint-plugin-local/tests/code-no-redundant-has-before-delete-test.ts b/.eslint-plugin-local/tests/code-no-redundant-has-before-delete-test.ts
new file mode 100644
index 00000000000..f87c8f87705
--- /dev/null
+++ b/.eslint-plugin-local/tests/code-no-redundant-has-before-delete-test.ts
@@ -0,0 +1,38 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+export function testRedundantHasBeforeDelete() {
+	const m = new Map<string, number>();
+	const s = new Set<string>();
+
+	// Invalid cases
+	m.delete('key');
+
+	s.delete('key');
+
+	// Cases with else clause
+	if (!m.delete('key')) {
+		console.log('not found');
+	}
+
+	if (m.delete('key')) {
+		console.log('deleted');
+	} else {
+		console.log('not found');
+	}
+
+	// Valid cases
+	m.delete('key');
+	s.delete('key');
+
+	if (m.has('key')) {
+		console.log('deleting');
+		m.delete('key');
+	}
+
+	if (m.has('key')) {
+		m.delete('otherKey');
+	}
+}
diff --git a/eslint.config.js b/eslint.config.js
index 9d83f9269e3..a2c242bcc19 100644
--- a/eslint.config.js
+++ b/eslint.config.js
@@ -92,6 +92,7 @@ export default tseslint.config(
 			'local/code-no-localized-model-description': 'warn',
 			'local/code-policy-localization-key-match': 'warn',
 			'local/code-no-localization-template-literals': 'error',
+			'local/code-no-redundant-has-before-delete': 'warn',
 			'local/code-no-deep-import-of-internal': ['error', { '.*Internal': true, 'searchExtTypesInternal': false }],
 			'local/code-layering': [
 				'warn',
diff --git a/src/vs/base/common/lifecycle.ts b/src/vs/base/common/lifecycle.ts
index f78aca05b53..2345bfd7028 100644
--- a/src/vs/base/common/lifecycle.ts
+++ b/src/vs/base/common/lifecycle.ts
@@ -505,8 +505,7 @@ export class DisposableStore implements IDisposable {
 		if (!o) {
 			return;
 		}
-		if (this._toDispose.has(o)) {
-			this._toDispose.delete(o);
+		if (this._toDispose.delete(o)) {
 			setParentOfDisposable(o, null);
 		}
 	}
diff --git a/src/vs/base/common/paging.ts b/src/vs/base/common/paging.ts
index 295600dac63..74123dd25b5 100644
--- a/src/vs/base/common/paging.ts
+++ b/src/vs/base/common/paging.ts
@@ -258,9 +258,7 @@ export class PageIteratorPager<T> implements IPager<T> {
 			}
 			return this.cachedPages[pageIndex];
 		} finally {
-			if (this.pendingRequests.has(pageIndex)) {
-				this.pendingRequests.delete(pageIndex);
-			}
+			this.pendingRequests.delete(pageIndex);
 		}
 	}
 
diff --git a/src/vs/platform/files/common/inMemoryFilesystemProvider.ts b/src/vs/platform/files/common/inMemoryFilesystemProvider.ts
index 54effa0ce0c..82ff1b532c7 100644
--- a/src/vs/platform/files/common/inMemoryFilesystemProvider.ts
+++ b/src/vs/platform/files/common/inMemoryFilesystemProvider.ts
@@ -201,8 +201,7 @@ export class InMemoryFileSystemProvider extends Disposable implements
 		const dirname = resources.dirname(resource);
 		const basename = resources.basename(resource);
 		const parent = this._lookupAsDirectory(dirname, false);
-		if (parent.entries.has(basename)) {
-			parent.entries.delete(basename);
+		if (parent.entries.delete(basename)) {
 			parent.mtime = Date.now();
 			parent.size -= 1;
 			this._fireSoon({ type: FileChangeType.UPDATED, resource: dirname }, { resource, type: FileChangeType.DELETED });
diff --git a/src/vs/platform/lifecycle/electron-main/lifecycleMainService.ts b/src/vs/platform/lifecycle/electron-main/lifecycleMainService.ts
index eed06364769..bd41c5619e1 100644
--- a/src/vs/platform/lifecycle/electron-main/lifecycleMainService.ts
+++ b/src/vs/platform/lifecycle/electron-main/lifecycleMainService.ts
@@ -433,9 +433,7 @@ export class LifecycleMainService extends Disposable implements ILifecycleMainSe
 
 			// The window already acknowledged to be closed
 			const windowId = window.id;
-			if (this.windowToCloseRequest.has(windowId)) {
-				this.windowToCloseRequest.delete(windowId);
-
+			if (this.windowToCloseRequest.delete(windowId)) {
 				return;
 			}
 
diff --git a/src/vs/platform/tunnel/node/sharedProcessTunnelService.ts b/src/vs/platform/tunnel/node/sharedProcessTunnelService.ts
index 46500cf661b..f6cb50f5482 100644
--- a/src/vs/platform/tunnel/node/sharedProcessTunnelService.ts
+++ b/src/vs/platform/tunnel/node/sharedProcessTunnelService.ts
@@ -81,9 +81,8 @@ export class SharedProcessTunnelService extends Disposable implements ISharedPro
 			throw new Error(`Could not create tunnel`);
 		}
 
-		if (this._disposedTunnels.has(id)) {
+		if (this._disposedTunnels.delete(id)) {
 			// This tunnel was disposed in the meantime
-			this._disposedTunnels.delete(id);
 			tunnelData.dispose();
 			await tunnel.dispose();
 			throw canceled();
diff --git a/src/vs/workbench/api/browser/mainThreadShare.ts b/src/vs/workbench/api/browser/mainThreadShare.ts
index cb63bb3fd03..115b45ce0b8 100644
--- a/src/vs/workbench/api/browser/mainThreadShare.ts
+++ b/src/vs/workbench/api/browser/mainThreadShare.ts
@@ -41,12 +41,8 @@ export class MainThreadShare implements MainThreadShareShape {
 	}
 
 	$unregisterShareProvider(handle: number): void {
-		if (this.providers.has(handle)) {
-			this.providers.delete(handle);
-		}
-		if (this.providerDisposables.has(handle)) {
-			this.providerDisposables.delete(handle);
-		}
+		this.providers.delete(handle);
+		this.providerDisposables.delete(handle);
 	}
 
 	dispose(): void {
diff --git a/src/vs/workbench/api/common/extHostCodeInsets.ts b/src/vs/workbench/api/common/extHostCodeInsets.ts
index 01cc0023b1d..707c9621c17 100644
--- a/src/vs/workbench/api/common/extHostCodeInsets.ts
+++ b/src/vs/workbench/api/common/extHostCodeInsets.ts
@@ -107,8 +107,7 @@ export class ExtHostEditorInsets implements ExtHostEditorInsetsShape {
 			readonly onDidDispose: vscode.Event<void> = onDidDispose.event;
 
 			dispose(): void {
-				if (that._insets.has(handle)) {
-					that._insets.delete(handle);
+				if (that._insets.delete(handle)) {
 					that._proxy.$disposeEditorInset(handle);
 					onDidDispose.fire();
 
diff --git a/src/vs/workbench/api/common/extHostTesting.ts b/src/vs/workbench/api/common/extHostTesting.ts
index 1cef0298f32..423b6d3b33a 100644
--- a/src/vs/workbench/api/common/extHostTesting.ts
+++ b/src/vs/workbench/api/common/extHostTesting.ts
@@ -1071,8 +1071,7 @@ class MirroredChangeCollector implements IncrementalChangeCollector<MirroredColl
 	 * @inheritdoc
 	 */
 	public remove(node: MirroredCollectionTestItem): void {
-		if (this.added.has(node)) {
-			this.added.delete(node);
+		if (this.added.delete(node)) {
 			return;
 		}
 
diff --git a/src/vs/workbench/browser/parts/statusbar/statusbarModel.ts b/src/vs/workbench/browser/parts/statusbar/statusbarModel.ts
index 5f0264991d0..7e033e21422 100644
--- a/src/vs/workbench/browser/parts/statusbar/statusbarModel.ts
+++ b/src/vs/workbench/browser/parts/statusbar/statusbarModel.ts
@@ -144,9 +144,7 @@ export class StatusbarViewModel extends Disposable {
 	}
 
 	show(id: string): void {
-		if (this.hidden.has(id)) {
-			this.hidden.delete(id);
-
+		if (this.hidden.delete(id)) {
 			this.updateVisibility(id, true);
 
 			this.saveState();
diff --git a/src/vs/workbench/contrib/chat/browser/agentSessions/agentSessionsViewFilter.ts b/src/vs/workbench/contrib/chat/browser/agentSessions/agentSessionsViewFilter.ts
index 0db76e1403c..59973405329 100644
--- a/src/vs/workbench/contrib/chat/browser/agentSessions/agentSessionsViewFilter.ts
+++ b/src/vs/workbench/contrib/chat/browser/agentSessions/agentSessionsViewFilter.ts
@@ -133,9 +133,7 @@ export class AgentSessionsViewFilter extends Disposable {
 				}
 				run(): void {
 					const providerExcludes = new Set(that.excludes.providers);
-					if (providerExcludes.has(provider.id)) {
-						providerExcludes.delete(provider.id);
-					} else {
+					if (!providerExcludes.delete(provider.id)) {
 						providerExcludes.add(provider.id);
 					}
 
@@ -170,9 +168,7 @@ export class AgentSessionsViewFilter extends Disposable {
 				}
 				run(): void {
 					const stateExcludes = new Set(that.excludes.states);
-					if (stateExcludes.has(state.id)) {
-						stateExcludes.delete(state.id);
-					} else {
+					if (!stateExcludes.delete(state.id)) {
 						stateExcludes.add(state.id);
 					}
 
diff --git a/src/vs/workbench/contrib/chat/browser/chatManagement/chatModelsViewModel.ts b/src/vs/workbench/contrib/chat/browser/chatManagement/chatModelsViewModel.ts
index 482c495d720..ad145de5cd7 100644
--- a/src/vs/workbench/contrib/chat/browser/chatManagement/chatModelsViewModel.ts
+++ b/src/vs/workbench/contrib/chat/browser/chatManagement/chatModelsViewModel.ts
@@ -362,9 +362,7 @@ export class ChatModelsViewModel extends EditorModel {
 
 	toggleVendorCollapsed(vendorEntry: IVendorItemEntry): void {
 		this.selectedEntry = vendorEntry;
-		if (this.collapsedVendors.has(vendorEntry.vendorEntry.vendor)) {
-			this.collapsedVendors.delete(vendorEntry.vendorEntry.vendor);
-		} else {
+		if (!this.collapsedVendors.delete(vendorEntry.vendorEntry.vendor)) {
 			this.collapsedVendors.add(vendorEntry.vendorEntry.vendor);
 		}
 		this.filter(this.searchValue);
diff --git a/src/vs/workbench/contrib/notebook/browser/services/notebookEditorServiceImpl.ts b/src/vs/workbench/contrib/notebook/browser/services/notebookEditorServiceImpl.ts
index d57424d08f0..c8d6c88b853 100644
--- a/src/vs/workbench/contrib/notebook/browser/services/notebookEditorServiceImpl.ts
+++ b/src/vs/workbench/contrib/notebook/browser/services/notebookEditorServiceImpl.ts
@@ -272,8 +272,7 @@ export class NotebookEditorWidgetService implements INotebookEditorService {
 
 	removeNotebookEditor(editor: INotebookEditor): void {
 		const notebookUri = editor.getViewModel()?.notebookDocument.uri;
-		if (this._notebookEditors.has(editor.getId())) {
-			this._notebookEditors.delete(editor.getId());
+		if (this._notebookEditors.delete(editor.getId())) {
 			this._onNotebookEditorsRemove.fire(editor);
 		}
 		if (this._mostRecentRepl.get() === notebookUri?.toString()) {
diff --git a/src/vs/workbench/contrib/notebook/browser/viewModel/notebookViewModelImpl.ts b/src/vs/workbench/contrib/notebook/browser/viewModel/notebookViewModelImpl.ts
index ca7a0dabfe6..25755ec15f7 100644
--- a/src/vs/workbench/contrib/notebook/browser/viewModel/notebookViewModelImpl.ts
+++ b/src/vs/workbench/contrib/notebook/browser/viewModel/notebookViewModelImpl.ts
@@ -731,9 +731,7 @@ export class NotebookViewModel extends Disposable implements EditorFoldingStateD
 				this._decorationIdToCellMap.delete(id);
 			}
 
-			if (this._overviewRulerDecorations.has(id)) {
-				this._overviewRulerDecorations.delete(id);
-			}
+			this._overviewRulerDecorations.delete(id);
 		});
 
 		const result: string[] = [];
diff --git a/src/vs/workbench/contrib/remote/browser/remoteExplorer.ts b/src/vs/workbench/contrib/remote/browser/remoteExplorer.ts
index 7adab723887..bc8534ed466 100644
--- a/src/vs/workbench/contrib/remote/browser/remoteExplorer.ts
+++ b/src/vs/workbench/contrib/remote/browser/remoteExplorer.ts
@@ -800,10 +800,9 @@ class ProcAutomaticPortForwarding extends Disposable {
 				}
 				await this.remoteExplorerService.close(value, TunnelCloseReason.AutoForwardEnd);
 				removedPorts.push(value.port);
-			} else if (this.notifiedOnly.has(key)) {
-				this.notifiedOnly.delete(key);
+			} else if (this.notifiedOnly.delete(key)) {
 				removedPorts.push(value.port);
-			} else if (this.initialCandidates.has(key)) {
+			} else {
 				this.initialCandidates.delete(key);
 			}
 		}
diff --git a/src/vs/workbench/contrib/scm/browser/scmViewService.ts b/src/vs/workbench/contrib/scm/browser/scmViewService.ts
index 1795e0f25f8..f136b88233b 100644
--- a/src/vs/workbench/contrib/scm/browser/scmViewService.ts
+++ b/src/vs/workbench/contrib/scm/browser/scmViewService.ts
@@ -190,16 +190,12 @@ export class SCMViewService implements ISCMViewService {
 				const removed = new Set(last.removed);
 
 				for (const repository of e.added) {
-					if (removed.has(repository)) {
-						removed.delete(repository);
-					} else {
+					if (!removed.delete(repository)) {
 						added.add(repository);
 					}
 				}
 				for (const repository of e.removed) {
-					if (added.has(repository)) {
-						added.delete(repository);
-					} else {
+					if (!added.delete(repository)) {
 						removed.add(repository);
 					}
 				}
diff --git a/src/vs/workbench/contrib/search/browser/searchTreeModel/folderMatch.ts b/src/vs/workbench/contrib/search/browser/searchTreeModel/folderMatch.ts
index 22eead9d1c4..7e0db52044e 100644
--- a/src/vs/workbench/contrib/search/browser/searchTreeModel/folderMatch.ts
+++ b/src/vs/workbench/contrib/search/browser/searchTreeModel/folderMatch.ts
@@ -225,9 +225,7 @@ export class FolderMatchImpl extends Disposable implements ISearchTreeFolderMatc
 
 	doAddFile(fileMatch: ISearchTreeFileMatch): void {
 		this._fileMatches.set(fileMatch.resource, fileMatch);
-		if (this._unDisposedFileMatches.has(fileMatch.resource)) {
-			this._unDisposedFileMatches.delete(fileMatch.resource);
-		}
+		this._unDisposedFileMatches.delete(fileMatch.resource);
 	}
 
 	hasOnlyReadOnlyMatches(): boolean {
@@ -264,9 +262,7 @@ export class FolderMatchImpl extends Disposable implements ISearchTreeFolderMatc
 
 		this._folderMatches.set(folderMatch.resource, folderMatch);
 		this._folderMatchesMap.set(folderMatch.resource, folderMatch);
-		if (this._unDisposedFolderMatches.has(folderMatch.resource)) {
-			this._unDisposedFolderMatches.delete(folderMatch.resource);
-		}
+		this._unDisposedFolderMatches.delete(folderMatch.resource);
 	}
 
 	private async batchReplace(matches: (ISearchTreeFileMatch | ISearchTreeFolderMatchWithResource)[]): Promise<any> {
diff --git a/src/vs/workbench/contrib/tasks/browser/abstractTaskService.ts b/src/vs/workbench/contrib/tasks/browser/abstractTaskService.ts
index f7070c78be5..30fce10b2d2 100644
--- a/src/vs/workbench/contrib/tasks/browser/abstractTaskService.ts
+++ b/src/vs/workbench/contrib/tasks/browser/abstractTaskService.ts
@@ -1286,16 +1286,14 @@ export abstract class AbstractTaskService extends Disposable implements ITaskSer
 	}
 
 	public removeRecentlyUsedTask(taskRecentlyUsedKey: string) {
-		if (this._getTasksFromStorage('historical').has(taskRecentlyUsedKey)) {
-			this._getTasksFromStorage('historical').delete(taskRecentlyUsedKey);
+		if (this._getTasksFromStorage('historical').delete(taskRecentlyUsedKey)) {
 			this._saveRecentlyUsedTasks();
 		}
 	}
 
 	public removePersistentTask(key: string) {
 		this._log(nls.localize('taskService.removePersistentTask', 'Removing persistent task {0}', key), true);
-		if (this._getTasksFromStorage('persistent').has(key)) {
-			this._getTasksFromStorage('persistent').delete(key);
+		if (this._getTasksFromStorage('persistent').delete(key)) {
 			this._savePersistentTasks();
 		}
 	}
diff --git a/src/vs/workbench/contrib/tasks/common/problemCollectors.ts b/src/vs/workbench/contrib/tasks/common/problemCollectors.ts
index dbad5612b09..13ef3e3d26a 100644
--- a/src/vs/workbench/contrib/tasks/common/problemCollectors.ts
+++ b/src/vs/workbench/contrib/tasks/common/problemCollectors.ts
@@ -546,8 +546,7 @@ export class WatchingProblemCollector extends AbstractProblemCollector implement
 				} else {
 					this._onDidRequestInvalidateLastMarker.fire();
 				}
-				if (this._activeBackgroundMatchers.has(background.key)) {
-					this._activeBackgroundMatchers.delete(background.key);
+				if (this._activeBackgroundMatchers.delete(background.key)) {
 					this.resetCurrentResource();
 					this._onDidStateChange.fire(IProblemCollectorEvent.create(ProblemCollectorEventKind.BackgroundProcessingEnds));
 					result = true;
diff --git a/src/vs/workbench/contrib/timeline/browser/timelinePane.ts b/src/vs/workbench/contrib/timeline/browser/timelinePane.ts
index 79b8558ecd5..efca4183366 100644
--- a/src/vs/workbench/contrib/timeline/browser/timelinePane.ts
+++ b/src/vs/workbench/contrib/timeline/browser/timelinePane.ts
@@ -1362,9 +1362,7 @@ class TimelinePaneCommands extends Disposable {
 					});
 				}
 				run(accessor: ServicesAccessor, ...args: unknown[]) {
-					if (excluded.has(source.id)) {
-						excluded.delete(source.id);
-					} else {
+					if (!excluded.delete(source.id)) {
 						excluded.add(source.id);
 					}
 
diff --git a/src/vs/workbench/services/authentication/browser/authenticationService.ts b/src/vs/workbench/services/authentication/browser/authenticationService.ts
index c3aba1e9b86..3b4df87a6c3 100644
--- a/src/vs/workbench/services/authentication/browser/authenticationService.ts
+++ b/src/vs/workbench/services/authentication/browser/authenticationService.ts
@@ -239,9 +239,7 @@ export class AuthenticationService extends Disposable implements IAuthentication
 		if (provider) {
 			this._authenticationProviders.delete(id);
 			// If this is a dynamic provider, remove it from the set of dynamic providers
-			if (this._dynamicAuthenticationProviderIds.has(id)) {
-				this._dynamicAuthenticationProviderIds.delete(id);
-			}
+			this._dynamicAuthenticationProviderIds.delete(id);
 			this._onDidUnregisterAuthenticationProvider.fire({ id, label: provider.label });
 		}
 		this._authenticationProviderDisposables.deleteAndDispose(id);
diff --git a/src/vs/workbench/services/policies/common/accountPolicyService.ts b/src/vs/workbench/services/policies/common/accountPolicyService.ts
index d81da4dffe1..2fd9117d80f 100644
--- a/src/vs/workbench/services/policies/common/accountPolicyService.ts
+++ b/src/vs/workbench/services/policies/common/accountPolicyService.ts
@@ -44,8 +44,7 @@ export class AccountPolicyService extends AbstractPolicyService implements IPoli
 					updated.push(key);
 				}
 			} else {
-				if (this.policies.has(key)) {
-					this.policies.delete(key);
+				if (this.policies.delete(key)) {
 					updated.push(key);
 				}
 			}
diff --git a/src/vs/workbench/services/remote/common/tunnelModel.ts b/src/vs/workbench/services/remote/common/tunnelModel.ts
index ea8629af1be..469d8f1b4a9 100644
--- a/src/vs/workbench/services/remote/common/tunnelModel.ts
+++ b/src/vs/workbench/services/remote/common/tunnelModel.ts
@@ -542,8 +542,7 @@ export class TunnelModel extends Disposable {
 
 	private async onTunnelClosed(address: { host: string; port: number }, reason: TunnelCloseReason) {
 		const key = makeAddress(address.host, address.port);
-		if (this.forwarded.has(key)) {
-			this.forwarded.delete(key);
+		if (this.forwarded.delete(key)) {
 			await this.storeForwarded();
 			this._onClosePort.fire(address);
 		}
@@ -907,9 +906,7 @@ export class TunnelModel extends Disposable {
 				detail: value.detail,
 				pid: value.pid
 			});
-			if (removedCandidates.has(addressKey)) {
-				removedCandidates.delete(addressKey);
-			}
+			removedCandidates.delete(addressKey);
 			const forwardedValue = mapHasAddressLocalhostOrAllInterfaces(this.forwarded, value.host, value.port);
 			if (forwardedValue) {
 				forwardedValue.runningProcess = value.detail;