`#pragma pack(1)` struct containing another packed struct is not packed itself.

[reitermarkus]

Input C/C++ Header

#include <stdint.h>

#pragma pack(1)

typedef struct {
  uint64_t value;
} first_t;

typedef struct {
  first_t value;
} second_t;

#pragma pack()

Bindgen Invocation

$ bindgen input.h

Actual Results

#[repr(C, packed)]
#[derive(Debug, Copy, Clone)]
pub struct first_t {
    pub value: u64,
}

#[repr(C)]
#[derive(Debug, Copy, Clone)]
pub struct second_t {
    pub value: first_t,
}

Expected Results

The second_t struct should be #[repr(C, packed)], not just #[repr(C)].

#[repr(C, packed)]
#[derive(Debug, Copy, Clone)]
pub struct first_t {
    pub value: u64,
}

#[repr(C, packed)]
#[derive(Debug, Copy, Clone)]
pub struct second_t {
    pub value: first_t,
}

[emilio]

The way we detect packed structs with #pragma pack() is a bit hacky, and fails for this case:

https://github.com/rust-lang/rust-bindgen/blob/4d18f7606a2bc8a18b181b3e9639c9464a9dc896/src/ir/comp.rs#L1621-L1636

It's not particularly trivial to do better I think, but maybe libclang now exposes the relevant attributes?