extensions/typescript-language-features/src/languageFeatures/documentHighlight.ts/TypeScriptDocumentHighlightProvider/provideDocumentHighlights
class TypeScriptDocumentHighlightProvider:	public async provideDocumentHighlights(
		document: vscode.TextDocument,
		position: vscode.Position,
		token: vscode.CancellationToken
	): Promise<vscode.DocumentHighlight[]> {
		const file = this.client.toOpenedFilePath(document);
		if (!file) {
			return [];
		}

		const args = {
			...typeConverters.Position.toFileLocationRequestArgs(file, position),
			filesToSearch: [file]
		};
		const response = await this.client.execute('documentHighlights', args, token);
		if (response.type !== 'response' || !response.body) {
			return [];
		}

		return response.body
			.filter(highlight => highlight.file === file)
			.map(convertDocumentHighlight)
			.flat();
	}