src/vs/workbench/api/common/extHostLanguageFeatures.ts/CompletionsAdapter/resolveCompletionItem
class CompletionsAdapter:	async resolveCompletionItem(id: extHostProtocol.ChainedCacheId, token: CancellationToken): Promise<extHostProtocol.ISuggestDataDto | undefined> {

		if (typeof this._provider.resolveCompletionItem !== 'function') {
			return undefined;
		}

		const item = this._cache.get(...id);
		if (!item) {
			return undefined;
		}

		const resolvedItem = await this._provider.resolveCompletionItem!(item, token);

		if (!resolvedItem) {
			return undefined;
		}

		return this._convertCompletionItem(resolvedItem, id);
	}