Compiler segfaults using @unionInit with a slice of runtime scalar

[doclic]

Zig Version

0.14.1

Steps to Reproduce and Observed Behavior

The compiler will crash with a SIGSEGV when trying to compile this code:

pub const Foo = union(enum) {
    a: void,
};
pub var bar: u8 = 'a';

pub fn main() void {
    _ = @unionInit(Foo, &.{bar}, {});
}

Command used was zig build-exe example.zig

Expected Behavior

An error, as this code is still not correct.

[BeigeHornet151]

Zig Compiler Crash with @unionInit and a Runtime Slice

Summary

In Zig 0.14.1, using @unionInit incorrectly with a slice of a runtime scalar causes a segmentation fault during compilation. This is due to passing an invalid argument type to the function.

Problematic Code

pub const Foo = union(enum) {
    a: void,
};

pub var bar: u8 = 'a';

pub fn main() void {
    _ = @unionInit(Foo, &.{bar}, {});
}

Cause

• @unionInit expects a union tag as a string and a matching value.
• The input &.{bar} is a slice, not a valid tag.
• The union Foo has a single tag a which takes a void, so the input must match that signature.

Solution

Replace the invalid usage with a valid union tag and matching value:

Corrected Code

pub const Foo = union(enum) {
    a: void,
};

pub var bar: u8 = 'a';

pub fn main() void {
    const value = @unionInit(Foo, "a", {});
    _ = value;
}

Resolution

Changing the code to use a string tag ("a") and the corresponding value ({}) resolves the segmentation fault. This ensures @unionInit is used with valid inputs and compiles as expected.

Expected Compiler Behavior

Instead of crashing, the compiler should report an error when an invalid tag type is passed to @unionInit.