Non-exported recursive type alias is inlined until it falls back to any in declarations

[dragomirtitian]

🔎 Search Terms

declarations recursive types

🕗 Version & Regression Information

• This is the behavior in every version I tried (before 4.4 it was either a stack overflow crash or an error on the recursive type)

⏯ Playground Link

Playground Link

💻 Code

// @declaration: true
// @filename: utils.ts 

type Recursive<T>  =  T extends Array<infer V>? Recursive<V>: T;

export const f = <T>(): Recursive<T> => { return null! } 

// @filename: index.ts 
import { f } from './utils';
export const a = f;

🙁 Actual behavior

In declarations, the type for a is printed as a: () => T extends (infer V)[] ? V extends (infer V)[] ? V extends (infer V)[] ? V extends (infer V)[] ? V extends (infer V)[] ? V extends (infer V)[] ? V extends (infer V)[] ? V extends (infer V)[] ? V extends (infer V)[] ? V extends (infer V)[] ? V extends (infer V)[] ? any : V : V : V : V : V : V : V : V : V : V : T;

🙂 Expected behavior

Recursive can't be represented without falling back to any (as seen above) so it should just be an error instead of silently to any

Additional information about the issue

Related to #55832

[jakebailey]

Generally, I feel like it'd be even better to always emit some sort of declaration error whenever declaration emit synthesizes an any out of nowhere...

[dragomirtitian]

I'll open a PR after 5.5. I tried locally and there are several places that now have errors, but in my opinion they are all good. Maybe we have just a carveout if someone is not using noImplicitAny (although hopefully nobody is actually doing that 😅)

[waynebloss]

I think this is the same issue I'm having, but I'm not sure.

Problem description within...

// Exported from `@mylib/dev/jrfs`:

export interface FileOf<D = unknown, M = unknown> {
  data: D;
  meta: M;
}
export type FileTypes<FT> = Record<keyof FT & string, FileOf>;

// Exported from `@mylib/dev/features/db`:

export interface DbDesign {
  db: DbModel;
}

export interface DbDesignFileMeta {
  test: boolean;
}

export type DbDesignFile = FileOf<DbDesign, DbDesignFileMeta>;

In the app project which imports from @mylib, when I use the DbDesignFile type exported from @mylib/dev, then VS Code shows the wrong type (const data: FileOf<DbDesign, DbDesignFileMeta>) in the tooltip and autocomplete doesn't work and it acts like the found data is any...

import { DbDesignFile } from "@mylib/dev/features/db";

interface ProjectFileTypes {
  db: DbDesignFile;
}

// Try it out:

class Yada<FT extends FileTypes<FT>> {
  async findTypes<K extends keyof FT & string>(
    type: K,
  ): Promise<
    Array<{
      node: any;
      data: Required<FT[K]>["data"];
    }>
  > {
    return [];
  }
}
const yada = new Yada<ProjectFileTypes>();
const nodes = await yada.findTypes("db");
for (const { node, data } of nodes) {
  // TODO: Figure out why `data` is treated like `any` here:
  console.log("FOUND", node.name, data);
}

However, if I re-define the DbDesignFile type alias in my app project then data from the yada.findTypes call above correctly shows and autocompletes type DbDesign...

import { FileOf } from "@mylib/dev/jrfs";
import { DbDesign, DbDesignFileMeta } from "@mylib/dev/features/db";

type DbDesignFile= FileOf<DbDesign, DbDesignFileMeta>;

interface ProjectFileTypes {
  db: DbDesignFile;
}

UPDATE: I figured out my own issue - my library's type declarations were being created with import type {...} from "@/jrfs"; because I don't have anything in place to fix tsc created alias import paths. Once I changed those to use relative import paths it worked. So, never mind, sorry for the noise!