René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Recursive type definitions regression in 3.4.0","articleBody":"\u003c!-- 🚨 STOP 🚨 𝗦𝗧𝗢𝗣 🚨 𝑺𝑻𝑶𝑷 🚨\r\n\r\nHalf of all issues filed here are duplicates, answered in the FAQ, or not appropriate for the bug tracker. Even if you think you've found a *bug*, please read the FAQ first, especially the Common \"Bugs\" That Aren't Bugs section!\r\n\r\nPlease help us by doing the following steps before logging an issue:\r\n  * Search: https://github.com/Microsoft/TypeScript/search?type=Issues\r\n  * Read the FAQ: https://github.com/Microsoft/TypeScript/wiki/FAQ\r\n\r\nPlease fill in the *entire* template below.\r\n--\u003e\r\n\r\n\u003c!-- Please try to reproduce the issue with `typescript@next`. It may have already been fixed. --\u003e\r\n**TypeScript Version:**  3.4.0-dev.201xxxxx\r\n\r\n\u003c!-- Search terms you tried before logging this (so others can find this issue more easily) --\u003e\r\n**Search Terms:**\r\n\r\nRecursive\r\nConditional\r\n\r\n**Code**\r\n\r\n```ts\r\ntype Action\u003c\r\n  Args extends any[],\r\n  Payload extends Record\u003cstring, any\u003e,\r\n  T extends string\r\n\u003e = ((...args: Args) =\u003e (Payload \u0026 { type: T })) \u0026 {\r\n  readonly type: T\r\n}\r\n\r\ntype AnyAction = Action\u003cany[], any, string\u003e\r\n\r\ntype CascadingActionMap = {\r\n  [name: string]: AnyAction | CascadingActionMap\r\n}\r\n\r\ntype Reducer\u003cS, T\u003e = (state: S, action: T) =\u003e S\r\n\r\ntype CascadingActionType\u003cT\u003e = T extends CascadingActionMap\r\n  ? { [K in keyof T]: ActionType\u003cT[K]\u003e }[keyof T]\r\n  : never\r\n\r\nexport type ActionType\u003cT\u003e = T extends AnyAction\r\n  ? ReturnType\u003cT\u003e\r\n  : T extends Reducer\u003cany, infer A\u003e\r\n  ? A\r\n  : CascadingActionType\u003cT\u003e\r\n```\r\n\r\n**Expected behavior:**\r\nNo errors. It's worth noting that it works in 3.3.4, with the correct derived type.\r\n\r\n**Actual behavior:**\r\nRunning `tsc` command line, it reports the following errors:\r\n\r\n```\r\nerror TS2456: Type alias 'CascadingActionType' circularly references itself.\r\n\r\n914 type CascadingActionType\u003cT\u003e = T extends CascadingActionMap\r\n         ~~~~~~~~~~~~~~~~~~~\r\n\r\nerror TS2315: Type 'ActionType' is not generic.\r\n\r\n915   ? { [K in keyof T]: ActionType\u003cT[K]\u003e }[keyof T]\r\n                          ~~~~~~~~~~~~~~~~\r\n\r\nerror TS2456: Type alias 'ActionType' circularly references itself.\r\n\r\n918 export type ActionType\u003cT\u003e = T extends AnyAction\r\n                ~~~~~~~~~~\r\n\r\nerror TS2315: Type 'CascadingActionType' is not generic.\r\n\r\n924   : CascadingActionType\u003cT\u003e\r\n        ~~~~~~~~~~~~~~~~~~~~~~\r\n```\r\n\r\n**Playground Link:** \u003c!-- A link to a TypeScript Playground \"Share\" link which demonstrates this behavior --\u003e\r\n\r\n**Related Issues:** \u003c!-- Did you find other bugs that looked similar? --\u003e\r\n","author":{"url":"https://github.com/TerenceZ","@type":"Person","name":"TerenceZ"},"datePublished":"2019-04-10T02:15:30.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":5},"url":"https://github.com/30841/TypeScript/issues/30841"}