Rather than a bug this is a question of the intended use of std.debug.assert.

One of the things I use assert for is to do expensive validation of state in debug builds expecting it to have no cost in a release build.

However that is not true of std.debug.assert as even in release fast the expression is fully evaluated. This is not what assert does in c.

Example in zig

const std = @import("std");

pub fn main() !void {
    std.debug.assert(expensiveFunction());
}

fn expensiveFunction() bool {
    std.io.getStdOut().writer().print("expensiveFunction ran\n", .{}) catch unreachable;
    return true;
}

$ zig run example.zig -ODebug
expensiveFunction ran

$ zig run example.zig -OReleaseFast
expensiveFunction ran

Example in c

#include <assert.h>
#include <stdbool.h>
#include <stdio.h>

bool expensiveFunction(void) {
    printf("expensiveFunction ran\n");
    return true;
}

void main(void) {
    assert(expensiveFunction());
}

$ zig run example.c -lc -ODebug
expensiveFunction ran

$ zig run example.c -lc -OReleaseFast