src/vs/editor/contrib/suggest/browser/suggestMemory.ts/PrefixMemory/select
class PrefixMemory:	override select(model: ITextModel, pos: IPosition, items: CompletionItem[]): number {
		const { word } = model.getWordUntilPosition(pos);
		if (!word) {
			return super.select(model, pos, items);
		}
		const key = `${model.getLanguageId()}/${word}`;
		let item = this._trie.get(key);
		if (!item) {
			item = this._trie.findSubstr(key);
		}
		if (item) {
			for (let i = 0; i < items.length; i++) {
				const { kind, insertText } = items[i].completion;
				if (kind === item.type && insertText === item.insertText) {
					return i;
				}
			}
		}
		return super.select(model, pos, items);
	}