E0028: Unreachable Pattern

A pattern in your match expression can never be reached because previous patterns already cover all its cases.

Example

enum Status {
    Active,
    Inactive,
}

fn check(s: Status) -> i64 {
    match s {
        Status::Active => { 1 },
        Status::Inactive => { 0 },
        Status::Active => { 2 },  // Error: unreachable pattern
    }
}

enum Color {
    Red,
    Green,
    Blue,
}

fn check(c: Color) -> i64 {
    match c {
        _ => { 0 },
        Color::Red => { 1 },  // Error: unreachable pattern (wildcard already matches everything)
    }
}

How to fix

Remove the unreachable pattern:

enum Status {
    Active,
    Inactive,
}

fn check(s: Status) -> i64 {
    match s {
        Status::Active => { 1 },
        Status::Inactive => { 0 },
    }
}

Or reorder your patterns so more specific ones come first:

enum Color {
    Red,
    Green,
    Blue,
}

fn check(c: Color) -> i64 {
    match c {
        Color::Red => { 1 },
        _ => { 0 },  // OK: wildcard comes after specific patterns
    }
}