Description
Bug Report
I've got an application that consumes two libraries like so:
The problem I'm facing is that the TypeScript build for LibB is outputting a collapsed "snapshot" of a union type that is imported from LibA rather than preserving a reference to the externally-defined union type. Because of this, when the application is using a newer version of LibA, the application cannot use types from the union that do not exist in the older version referenced by LibB.
As a workaround, I can update LibB to use the newer version of LibA, publish a new version, and update App to point to it, but since the implementation of LibB does not need to be updated, this step should be unnecessary.
I believe there have been various past proposals to solve this (such as in #35654), as well as a workarounds for specific use cases, but I haven't found a workaround that solves this particular case.
Thank you!
🔎 Search Terms
preserve type alias
prevent union type collapse
🕗 Version & Regression Information
v4.5.4, and other recent versions.
⏯ Playground Link
Because this issue only occurs when a project uses the emitted declarations from another project, I may not be able to provide a playground link.
💻 Code
# LibA (as of v1.1.0)
export type TypeFromLibA = "a" | "b";
# LibA (as of v1.5.0)
export type TypeFromLibA = "a" | "b" | "c";
# LibB
import type TypeFromLibA from "lib-a"; // ex. as npm library
export const functionFromLibB = (val: TypeFromLibA) => {
...
}
🙁 Actual behavior
# App
import functionFromLibB from "lib-b";
functionFromLibB("a"); // OK
functionFromLibB("c"); // Argument of type '"c"' is not assignable to parameter of type '"a" | "b"'.ts(2345)
🙂 Expected behavior
# App
import myFunction from "lib-b";
myFunction("a"); // OK
myFunction("c"); // OK