zig/test/cases/compile_errors/switching_with_non-exhaustive_enums.zig

const E = enum(u8) {
    a,
    b,
    _,
};
const U = union(E) {
    a: i32,
    b: u32,
};
pub export fn entry1() void {
    var e: E = .b;
    switch (e) { // error: switch not handling the tag `b`
        .a => {},
        _ => {},
    }
}
pub export fn entry2() void {
    var e: E = .b;
    switch (e) { // error: switch on non-exhaustive enum must include `else` or `_` prong
        .a => {},
        .b => {},
    }
}
pub export fn entry3() void {
    var u = U{.a = 2};
    switch (u) { // error: `_` prong not allowed when switching on tagged union
        .a => {},
        .b => {},
        _ => {},
    }
}

// error
// backend=stage2
// target=native
//
// :12:5: error: switch must handle all possibilities
// :12:5: note: unhandled enumeration value: 'b'
// :1:11: note: enum 'tmp.E' declared here
// :19:5: error: switch on non-exhaustive enum must include 'else' or '_' prong
// :26:5: error: '_' prong only allowed when switching on non-exhaustive enums
// :29:11: note: '_' prong here