Assigning packed struct inside another packed struct is miss aligned.

[bpeake13]

I have two packed structs that look something like this:

pub const Inner= packed struct {
    bits: u3,
    more_bits: u6,
};

pub const Outer = packed struct {
    padding: u5,
    inner: Inner,
};

Then when assigning a inner value to outer, the compiler will miss-align the assignment. For example the code:

var r: *volatile Outer = SOME_VALID_ADDRESS;

fn t(inner: Inner) void {
    r.inner = inner;
}

Will result in the first five bits of inner being assigned to padding.

zig version 0.9.0-dev.804+4c9d41730
Arch: Thumb
Model: Arm7tdmi
OS: Freestanding

[bpeake13]

Here is an example that observes the problem:
https://godbolt.org/z/x6Pzzj9sh

[bpeake13]

Further investigation, the assignment does seem to work, if the inner struct falls on its own alignment. So if the inner field in the top example is pushed to be after 16 bits worth of padding, it will assign correctly.