"Expression produces a union type that is too complex to represent" when using interfaces with large number of params for filtering and narrowing down certain keys

[SecondThundeR]

🔎 Search Terms

Expression produces a union type that is too complex to represent, 2590, ts2590

🕗 Version & Regression Information

• This behavior occurs in 5.4.2 and above. On 5.3.3 it works fine

⏯ Playground Link

https://www.typescriptlang.org/play?ts=5.4.2#code/KYDwDg9gTgLgBASwHY2FAZgQwMbDgVTABNNU4BvAKDhrgFdjTgB9BIgLjiToFsAjNAG5K1Wj2ABnCZgDmwAPydyccVNnBOEmFGQy4AX2G04wIglRFmq6XMUUTZi1ck2NcLTqR7DomtgAWmEhIwAA2zJBadsoBQSHhkTCa2roGRrSm5qbMscFhERBRSg5ZlrnxBVrJnt7pNNbqzFDAODAIEEjRKi6Nza3tSNWpPsYNck0t2G0dORB0KF1jLH1TA7PzSe4pXmm+iEihyCwAjnRoAJ5dyIchzKcXQzsjtAGFwEisB0cTEnShMF1XhJ3p8bstJH9Nh5hnU4NhMKFQnwcABrO5nKCXYrwxHI7Bo+6Yx61PYSfwIMBgXToi5dMkUqleGlErY1XbGMDNHL+YD4uYwZlY+yclgBXko-mC4ns2iQRFdOWhaXPGiK5hBCQAdzQCogiPVSC1aGVsJ4525pGc-B1xTNFoF4mtUBNe1iDuATsBgXdTpdxjdzAAVhBkBN7kV7AHg6HmuGodsSf7vcw+BBCgDscnU+m-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-W5NJcO1srvM9s48YzvDgAZDtosIAiA6u+7ACiIDYKEdCFwO1dzil4v4JztuFyHphUT7XAuUIj3PfzYChD5mBJz5zS-P8cB8D5yAQz1qTmDDcMI-lPNh+OEs8k+dASKkmPAlnE9OcjDqrkdCFzfngVodAESPzLngXaGADpEybqOM2U4PJznOnXL2UwtoYObpOVuDtNRID2M7Uiphh7FnZuRVB7Ue7nW1sYX2m8oDlWekgNG9VsZEJfo-c+l8UBoEhm0HYd8M7w0PmYdA6A0DvACnlGBcV3zkMocbYedclr-iQQtGhqBVJ7B7sPfRmVsrG2oYVPKJVuZ4zgJxNgRBQjAE1DVYAc1kE2w0cALa24pggBkseW2bduGoW2gnBAwIBwEOag9ceKdJwUNkQACToHwVx2iPHUT2J-YA25GK5OykQexjjnGcBMrVTAN1bEFIcU45oQ4qKyXiSgJJKSF4UD2LRQ0DFmKsQ4iZApuh1b5MKTUpiDivBAwKq9NACBsBwECOOBxUAJDsWEu0vMwAxISTfmE2ETZjCDitm4ta8VrowTWTQQSiFAJwFQgBTC2FjDGFyYxIZ1TimmTKRUuxbzalKWoZRNexgGkqOaQOP5XMMmPJeHRLpLE2LsT6WYPic5XlFOaMxd4MgJlwHYvMwpSy7zQHVpctAqyoU0FEuJJ8IQGqNJgKC8FKkYJktoE2XSbtDTwH8MkpKNK4B0uaduVZlBuV8EYh0DiSwVnCFFeKpAkqehyHVlJI8akKD6FWRyrQ7geVbllRKtC7EpUFXKPkRI7EMKrN+GKrJ24VX+PIBqmVyS5XbkNcanFpqEjpgtXOIVDqnWUCAA

💻 Code

export interface Update {
 update_id: number;

 message?: { message: string };
 edited_message?: { edited_message: string };
 channel_post?: { channel_post: string };
 edited_channel_post?: { edited_channel_post: string };
 message_reaction?: { message_reaction: string };
 message_reaction_count?: { message_reaction_count: string };
 inline_query?: { inline_query: string };
 chosen_inline_result?: { chosen_inline_result: string };
 callback_query?: { callback_query: string };
 shipping_query?: { shipping_query: string };
 pre_checkout_query?: { pre_checkout_query: string };
 poll?: { poll: string };
 poll_answer?: { poll_answer: string };
 my_chat_member?: { my_chat_member: string };
 chat_member?: { chat_member: string };
 chat_join_request?: { chat_join_request: string };
 chat_boost?: { chat_boost: string };
 removed_chat_boost?: { removed_chat_boost: string };
}

type FilterFunction<U extends Update, V extends U> = (up: U) => up is V;

export function matchFilter<U extends Update, Q extends FilterQuery>(
 filter: Q | Q[],
): FilterFunction<U, Filter<U, Q>> {
 // ^ errors out
 console.log("Matching", filter);
 return (up: U): up is Filter<U, Q> => !!up;
}

/** All valid filter queries (every update key except update_id) */
export type FilterQuery = keyof Omit<Update, "update_id">;

/** Narrow down an update object based on a filter query */
export type Filter<U extends Update, Q extends FilterQuery> = PerformQuery<
 U,
 RunQuery<Q>
>;

// generate an object structure that can be intersected with updates to narrow them down
type RunQuery<Q extends string> = Combine<L1Fragment<Q>, Q>;

// maps each part of the filter query to Record<"key", object>
type L1Fragment<Q extends string> = Q extends unknown ? Record<Q, object>
 : never;
// define all other fields from query as keys with value `undefined`
type Combine<U, K extends string> = U extends unknown
 ? U & Partial<Record<Exclude<K, keyof U>, undefined>>
 : never;

// apply a query result by intersecting it with update,
// and then using these values to override the actual update
type PerformQuery<U extends Update, R extends object> = R extends unknown
 ? FilteredEvent<U, Update & R>
 : never;

// narrow down an update by intersecting it with a different update
type FilteredEvent<E extends Update, U extends Update> =
 & E
 & Omit<U, "update_id">;

type Middleware<U extends Update> = (ctx: U) => unknown | Promise<unknown>;
class EventHub<U extends Update> {
 use(...middleware: Array<Middleware<U>>): EventHub<U> {
 console.log("Adding", middleware.length, "generic handlers");
 return this;
 }
 on<Q extends FilterQuery>(
 filter: Q | Q[],
 ...middleware: Array<Middleware<Filter<U, Q>>>
 // ^ errors out
 ): EventHub<Filter<U, Q>> {
 console.log("Adding", middleware.length, "handlers for", filter);
 return new EventHub<Filter<U, Q>>();
 }
}

🙁 Actual behavior

TypeScript compiler throws "Expression produces a union type that is too complex to represent" on Filter type instantiation with large interface

🙂 Expected behavior

TypeScript compiler shouldn't throw "Expression produces a union type that is too complex to represent" on Filter type instantiation with large interface

Additional information about the issue

On 5.3.3, such issue doesn't occur (even when we are adding more parameters to Update interface, e.g. additional 20-30 parameters)
But, on 5.4.2 it seems like limit for it is lowered down. When chat_boost and removed_chat_boost are removed, both Filter instantiations no longer throwing errors

[fatcerberus]

I assume you mean "properties" instead of "parameters"? There are no function types in the Update interface, let alone ones with large numbers of parameters.

[RyanCavanaugh]

Bisects to #56004

[RyanCavanaugh]

Anders Hejlsberg (@ahejlsberg) seems like Not a Defect to me but wanted to double-check

[ahejlsberg]

Since #56004 we reason more deeply (and correctly) about conditional type constraints, which definitely is a good thing. In this particular example it apparently causes us to materialize intersection types of the form ("foo" | Exclude<Q, "foo>) & ("bar | Exclude<Q, "bar">) & .... with 18 or so union types being intersected. This comes out to 2^18 possible constituents, which is above our 100,000 limit. Of course, the final intersection will actually only have 19 constituents because all of the literal types intersect to never. But we don't realize that.

Here's a simpler repro:

// Error: Expression produces a union type that is too complex to represent.
type Foo<T extends string> =
 & ("a" | T)
 & ("b" | T)
 & ("c" | T)
 & ("d" | T)
 & ("e" | T)
 & ("f" | T)
 & ("g" | T)
 & ("h" | T)
 & ("i" | T)
 & ("j" | T)
 & ("k" | T)
 & ("l" | T)
 & ("m" | T)
 & ("n" | T)
 & ("q" | T)
 & ("p" | T)
 & ("q" | T)
 & ("r" | T);

I'll think about ways to optimize this.