Misleading error message for missing properties in types composed of the intersection of certain multiple unions

Bug Report

🔎 Search Terms

intersection of union required property error message

🕗 Version & Regression Information

This is the behavior in every version I tried, and I reviewed the FAQ for entries about it

I use the playground and observed the same behavior for versions 4.2 through 4.9

⏯ Playground Link

Playground link with relevant code

💻 Code

type Arg =  (
  | {
      prefLabel?: string;
      showPref: false;
    }
  | {
      prefLabel: string;
      showPref?: true;
    }
) 
& (
    | { other: false; } 
    | { other: true; }
    );


const fn = (thing: Arg) => {};

fn({ showPref: false }); // <<< error on this line

fn({ showPref: false, other: true }); // <<< this is ok

🙁 Actual behavior

I see an error for fn({ showPref: false });:

Argument of type '{ showPref: false; }' is not assignable to parameter of type 'Arg'.
  Type '{ showPref: false; }' is not assignable to type '{ prefLabel: string; showPref?: true | undefined; } & { other: true; }'.
    Property 'prefLabel' is missing in type '{ showPref: false; }' but required in type '{ prefLabel: string; showPref?: true | undefined; }'.(2345)
input.tsx(7, 7): 'prefLabel' is declared here.

This is wrong because actually other is missing. The following line does not produce an error

🙂 Expected behavior

I would expect the error message to refer to the missing required property, not to an irrelevant union member

Start with the linked TypeScript Playground reproduction and compare the diagnostic for the two fn calls involving intersections of unions. Trace how the compiler selects the reported union member and missing property; done means the first call reports the missing other property rather than the irrelevant prefLabel property, while the second remains valid.