const value changes unexpectedly

[e0328eric]

Zig Version

0.12.0

Steps to Reproduce and Observed Behavior

The bug occurs at the const variable has_bug in the following code.

const std = @import("std");

const NewlineHandler = struct {
    source: []const u8,
    chr0: ?u8 = null,
    chr1: ?u8 = null,
    idx: usize = 0,

    const Self = @This();

    pub fn init(source: []const u8) Self {
        var output = Self{ .source = source };

        output.nextChar();
        output.nextChar();

        return output;
    }

    pub fn next(self: *Self) ?u8 {
        const has_bug: ?u8 = if (self.chr0 == '\r') blk: {
            if (self.chr1 == '\n') {
                self.nextChar();
                break :blk self.chr0;
            } else break :blk '\n';
        } else self.chr0;

        std.debug.print("value of `has_bug`: {?c}, type: {s}\n", .{ has_bug, @typeName(@TypeOf(has_bug)) });
        self.nextChar();
        std.debug.print("value of `has_bug`: {?c}, type: {s}\n", .{ has_bug, @typeName(@TypeOf(has_bug)) });

        return has_bug;
    }

    fn nextChar(self: *Self) void {
        self.chr0 = self.chr1;
        self.chr1 = if (self.idx >= self.source.len) null else self.source[self.idx];
        self.idx += 1;
    }
};

pub fn main() void {
    var nh = NewlineHandler.init("apple");
    std.debug.print("{?c}\n", .{nh.next()});
}

The output of this code is

value of `has_bug`: a, type: ?u8
value of `has_bug`: p, type: ?u8
p

Expected Behavior

Since the variable has_bug marked as const, and its type is ?u8, it should print

value of `has_bug`: a, type: ?u8
value of `has_bug`: a, type: ?u8
a