Introduce experimental fade out of unused variables

Gated behind undocumented setting. Requires proper vscode API

Part of #15710

extensions/typescript-language-features/src/features/diagnostics.ts

@@ -5,7 +5,7 @@
 
 import *  as vscode from 'vscode';
 
-class DiagnosticSet {
+export class DiagnosticSet {
 	private _map: ObjectMap<vscode.Diagnostic[]> = Object.create(null);
 
 	public set(

extensions/typescript-language-features/src/features/unusedHighlighter.ts

@@ -0,0 +1,73 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import * as vscode from 'vscode';
+import { DiagnosticSet } from './diagnostics';
+
+
+export class UnusedHighlighter {
+
+	private readonly _decorationType: vscode.TextEditorDecorationType;
+
+	private readonly _diagnostics = new DiagnosticSet();
+	private _validate: boolean = true;
+
+	constructor(
+	) {
+		this._decorationType = vscode.window.createTextEditorDecorationType({
+			opacity: '0.7'
+		});
+	}
+
+	public dispose() {
+		this._decorationType.dispose();
+	}
+
+	public reInitialize(): void {
+		this._diagnostics.clear();
+
+		for (const editor of vscode.window.visibleTextEditors) {
+			editor.setDecorations(this._decorationType, []);
+		}
+	}
+
+	public set validate(value: boolean) {
+		if (this._validate === value) {
+			return;
+		}
+
+		this._validate = value;
+		if (!value) {
+			for (const editor of vscode.window.visibleTextEditors) {
+				editor.setDecorations(this._decorationType, []);
+			}
+		}
+	}
+
+	public diagnosticsReceived(
+		file: vscode.Uri,
+		diagnostics: vscode.Diagnostic[]
+	): void {
+		// Undocumented flag to enable
+		if (!vscode.workspace.getConfiguration('typescript').get('showUnused.experimentalFade')) {
+			return;
+		}
+		this._diagnostics.set(file, diagnostics);
+		this._updateCurrentHighlights(file);
+	}
+
+	private _updateCurrentHighlights(file: vscode.Uri) {
+		for (const editor of vscode.window.visibleTextEditors) {
+			if (editor.document.uri.fsPath !== file.fsPath) {
+				continue;
+			}
+
+			const diagnostics = this._diagnostics.get(editor.document.uri);
+			if (diagnostics) {
+				editor.setDecorations(this._decorationType, diagnostics.map(x => x.range));
+			}
+		}
+	}
+}

extensions/typescript-language-features/src/languageProvider.ts

@@ -21,6 +21,7 @@ import { CachedNavTreeResponse } from './features/baseCodeLensProvider';
 import { memoize } from './utils/memoize';
 import { disposeAll } from './utils/dipose';
 import TelemetryReporter from './utils/telemetry';
+import { UnusedHighlighter } from './features/unusedHighlighter';
 
 const validateSetting = 'validate.enable';
 const suggestionSetting = 'suggestionActions.enabled';
@@ -29,6 +30,7 @@ const foldingSetting = 'typescript.experimental.syntaxFolding';
 export default class LanguageProvider {
 	private readonly diagnosticsManager: DiagnosticsManager;
 	private readonly bufferSyncSupport: BufferSyncSupport;
+	private readonly ununsedHighlighter: UnusedHighlighter;
 	private readonly fileConfigurationManager: FileConfigurationManager;
 
 	private readonly toUpdateOnConfigurationChanged: ({ updateConfiguration: () => void })[] = [];
@@ -56,6 +58,7 @@ export default class LanguageProvider {
 		}, this._validate);
 
 		this.diagnosticsManager = new DiagnosticsManager(description.diagnosticOwner);
+		this.ununsedHighlighter = new UnusedHighlighter();
 
 		workspace.onDidChangeConfiguration(this.configurationChanged, this, this.disposables);
 		this.configurationChanged();
@@ -226,6 +229,7 @@ export default class LanguageProvider {
 
 	public reInitialize(): void {
 		this.diagnosticsManager.reInitialize();
+		this.ununsedHighlighter.reInitialize();
 		this.bufferSyncSupport.reOpenDocuments();
 		this.bufferSyncSupport.requestAllDiagnostics();
 		this.fileConfigurationManager.reset();
@@ -261,6 +265,9 @@ export default class LanguageProvider {
 	public diagnosticsReceived(diagnosticsKind: DiagnosticKind, file: Uri, diagnostics: (Diagnostic & { reportUnnecessary: any })[]): void {
 		const config = workspace.getConfiguration(this.id);
 		const reportUnnecessary = config.get<boolean>('showUnused.enabled', true);
+		if (diagnosticsKind === DiagnosticKind.Suggestion) {
+			this.ununsedHighlighter.diagnosticsReceived(file, diagnostics.filter(diag => diag.reportUnnecessary));
+		}
 		this.diagnosticsManager.diagnosticsReceived(diagnosticsKind, file, diagnostics.filter(diag => diag.reportUnnecessary ? reportUnnecessary : true));
 	}