P.select loses type inference when used with multiple patterns in a single .with

[salemkode]

Describe the bug

When using P.select(P.string) with multiple patterns in the same .with clause, the handler parameter is not inferred as string.

Instead, it is inferred as the union of the full object shapes, rather than the selected value.

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TypeScript playground with a minimal reproduction case

Playground Link

import { match, P } from "ts-pattern";

const obj = {} as unknown;

const message = match(obj)
  .with(
    { errors: P.select(P.string) },
    { description: P.select(P.string) },
    (message) => {
      console.log("message", message);
      // ❌ Expected: message is string
      // ❌ Actual: message is inferred as object type
      return `Please enter ${message.replace("length", "characters")}`;
    }
  )
  .otherwise(() => "");

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Expected behavior

• The handler parameter should be inferred as string (from P.select(P.string)), even when multiple patterns are used.

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Actual behavior

• The handler parameter is inferred as the union of the object shapes ({ errors: string } | { description: string }), not the selected string.

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Versions

• TypeScript version: 5.9.2

[gvergnaud]

Thanks for the report. FYI P.select was never supported with multiple patterns because of these type inference shenanigans and unclear runtime behavior. Maybe one day