noUnusedLocals throws errors for "never" type.

Search Terms:
nounusedlocals never
nounusedlocals
never
never variable is not used error

Code

//NOTE: nounusedlocals is set to true in tsconfig.
enum Color {
  A,
  B,
}
function f(color: Color) {
  switch(color) {
    case Color.A:
      console.log("White");
      break;
    case Color.B:
      console.log("Black");
      break;
    default:
      const _:never = color;
  }
}

Expected behavior:
Compiles fine, prints nothing

Actual behavior:
Given variable _ is unused. _ is of type never which means it is expected to be never used. It is being declared as a compile time safety to ensure that we have cases over all the Color enum values.

Start by compiling the provided TypeScript snippet with noUnusedLocals enabled and confirm the diagnostic on the const _: never = color declaration. Trace the noUnusedLocals diagnostic for this declaration and compare it with the expected exhaustive-switch behavior. Done means the snippet compiles without reporting _ as unused while other genuinely unused locals remain diagnosed.