A function overload that is mistakenly unassignable to an intersection type.

[craigphicks]

🔎 Search Terms

#57087

🕗 Version & Regression Information

• This is the behavior in every version I tried (from 3.3.3~)
  • In versions before satisfies was implemented, had to test with extends - same result.

⏯ Playground Link

No response

💻 Code

interface C {
  (x:1):"1";
  (x:2):"20";
  (x:number):number;
}
interface B {
  (x:2):"2"
  (x:3):"30"
  (x:number):number;
}
interface A {
  (x:3):"3"
  (x:1):"10"
  (x:number):number;
}

function foo(x:1):"1";
function foo(x:2):"2";
function foo(x:3):"3";
function foo(x:number):number|"1"|"2"|"3"{
  if (x==1||x==2||x==3) return String(x) as any;
  return x;
}

// The `&`-intersection operator result should be independent of the order of it's operands.
foo satisfies A & B & C; // error (incorrect)
foo satisfies A & C & B; // error (incorrect)
foo satisfies B & A & C; // error (incorrect)
foo satisfies B & C & A; // error (incorrect)
foo satisfies C & A & B; // error (incorrect)
foo satisfies C & B & A; // error (incorrect)

// W stands for (attempted) "W"orkaround
type W = (A & B & C)|(A & C & B)|(B & A & C)|(B & C & A)|(C & A & B)|(C & B & A);
declare const w:W;
w(1);// "1","10"
w(2);// "2","20"
w(3);// "3","30"

foo(1); // "1"
foo(2); // "2"
foo(3); // "3"

// So the following should pass.
foo satisfies W; // error (incorrect)
//  ~~~~~~~~~
// Type '{ (x: 1): "1"; (x: 2): "2"; (x: 3): "3"; }' does not satisfy the expected type 'W'.
//  Type '{ (x: 1): "1"; (x: 2): "2"; (x: 3): "3"; }' is not assignable to type 'A & B & C'.(1360)

🙁 Actual behavior

Every satisifies statement is failing.

🙂 Expected behavior

Every satisifies statement should pass.

Additional information about the issue

Proposal #57087 should fix it.

[RyanCavanaugh]

Proposal #57087 should fix it.

👍

[typescript-bot]

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