rust-bindgen
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rust-lang
Failed to generate `Default` impl for arrays larger than 32 entries
Input C/C++ Header
#define CCHDEVICENAME 32
typedef long LONG;
typedef char CHAR;
typedef unsigned long DWORD;
typedef struct tagRECT
{
LONG left;
LONG top;
LONG right;
LONG bottom;
} RECT;
typedef struct tagMONITORINFO
{
DWORD cbSize;
RECT rcMonitor;
RECT rcWork;
DWORD dwFlags;
} MONITORINFO, *LPMONITORINFO;
typedef struct tagMONITORINFOEXA
{
MONITORINFO;
CHAR szDevice[CCHDEVICENAME];
} MONITORINFOEXA, *LPMONITORINFOEXA;
Bindgen Invocation
use std::env;
use std::path::PathBuf;
fn main() {
let bindings = bindgen::Builder::default()
.header_contents(
"input.h",
r#"
#define CCHDEVICENAME 32
typedef long LONG;
typedef char CHAR;
typedef unsigned long DWORD;
typedef struct tagRECT
{
LONG left;
LONG top;
LONG right;
LONG bottom;
} RECT;
typedef struct tagMONITORINFO
{
DWORD cbSize;
RECT rcMonitor;
RECT rcWork;
DWORD dwFlags;
} MONITORINFO, *LPMONITORINFO;
typedef struct tagMONITORINFOEXA
{
MONITORINFO;
CHAR szDevice[CCHDEVICENAME];
} MONITORINFOEXA, *LPMONITORINFOEXA;"#,
)
.derive_default(true)
.parse_callbacks(Box::new(bindgen::CargoCallbacks::new()))
.generate()
.expect("Unable to generate bindings");
let out_path = PathBuf::from(env::var("OUT_DIR").unwrap());
bindings
.write_to_file(out_path.join("bindings.rs"))
.expect("Couldn't write bindings!");
}
Actual Results
error[E0277]: the trait bound `[u8; 40]: Default` is not satisfied
--> D:\git-repos\bindgen-test\target\debug\build\bindgen-test-39d5729a71a2ce1c\out/bindings.rs:140:5
|
138 | #[derive(Debug, Default, Copy, Clone)]
| ------- in this derive macro expansion
139 | pub struct tagMONITORINFOEXA {
140 | pub __bindgen_padding_0: [u8; 40usize],
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Default` is not implemented for `[u8; 40]`
|
= help: the following other types implement trait `Default`:
[T; 0]
[T; 1]
[T; 2]
[T; 3]
[T; 4]
[T; 5]
[T; 6]
[T; 7]
and 27 others
= note: this error originates in the derive macro `Default` (in Nightly builds, run with -Z macro-backtrace for more info)
For more information about this error, try `rustc --explain E0277`.
error: could not compile `bindgen-test` (lib) due to 1 previous error
Caused by:
process didn't exit successfully: `sccache rustc --crate-name bindgen_test --edition=2021 src\lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=191 --crate-type lib --emit=dep-info,metadata,link -C embed-bitcode=no -C debuginfo=2 -C metadata=dfb5b3ab9206c6f2 -C extra-filename=-dfb5b3ab9206c6f2 --out-dir D:\git-repos\bindgen-test\target\debug\deps -C incremental=D:\git-repos\bindgen-test\target\debug\incremental -L dependency=D:\git-repos\bindgen-test\target\debug\deps` (exit code: 1)
and/or
/* automatically generated by rust-bindgen 0.69.4 */
pub const CCHDEVICENAME: u32 = 32;
pub type LONG = ::std::os::raw::c_long;
pub type CHAR = ::std::os::raw::c_char;
pub type DWORD = ::std::os::raw::c_ulong;
#[repr(C)]
#[derive(Debug, Default, Copy, Clone)]
pub struct tagRECT {
pub left: LONG,
pub top: LONG,
pub right: LONG,
pub bottom: LONG,
}
#[test]
fn bindgen_test_layout_tagRECT() {
const UNINIT: ::std::mem::MaybeUninit<tagRECT> = ::std::mem::MaybeUninit::uninit();
let ptr = UNINIT.as_ptr();
assert_eq!(
::std::mem::size_of::<tagRECT>(),
16usize,
concat!("Size of: ", stringify!(tagRECT))
);
assert_eq!(
::std::mem::align_of::<tagRECT>(),
4usize,
concat!("Alignment of ", stringify!(tagRECT))
);
assert_eq!(
unsafe { ::std::ptr::addr_of!((*ptr).left) as usize - ptr as usize },
0usize,
concat!(
"Offset of field: ",
stringify!(tagRECT),
"::",
stringify!(left)
)
);
assert_eq!(
unsafe { ::std::ptr::addr_of!((*ptr).top) as usize - ptr as usize },
4usize,
concat!(
"Offset of field: ",
stringify!(tagRECT),
"::",
stringify!(top)
)
);
assert_eq!(
unsafe { ::std::ptr::addr_of!((*ptr).right) as usize - ptr as usize },
8usize,
concat!(
"Offset of field: ",
stringify!(tagRECT),
"::",
stringify!(right)
)
);
assert_eq!(
unsafe { ::std::ptr::addr_of!((*ptr).bottom) as usize - ptr as usize },
12usize,
concat!(
"Offset of field: ",
stringify!(tagRECT),
"::",
stringify!(bottom)
)
);
}
pub type RECT = tagRECT;
#[repr(C)]
#[derive(Debug, Default, Copy, Clone)]
pub struct tagMONITORINFO {
pub cbSize: DWORD,
pub rcMonitor: RECT,
pub rcWork: RECT,
pub dwFlags: DWORD,
}
#[test]
fn bindgen_test_layout_tagMONITORINFO() {
const UNINIT: ::std::mem::MaybeUninit<tagMONITORINFO> = ::std::mem::MaybeUninit::uninit();
let ptr = UNINIT.as_ptr();
assert_eq!(
::std::mem::size_of::<tagMONITORINFO>(),
40usize,
concat!("Size of: ", stringify!(tagMONITORINFO))
);
assert_eq!(
::std::mem::align_of::<tagMONITORINFO>(),
4usize,
concat!("Alignment of ", stringify!(tagMONITORINFO))
);
assert_eq!(
unsafe { ::std::ptr::addr_of!((*ptr).cbSize) as usize - ptr as usize },
0usize,
concat!(
"Offset of field: ",
stringify!(tagMONITORINFO),
"::",
stringify!(cbSize)
)
);
assert_eq!(
unsafe { ::std::ptr::addr_of!((*ptr).rcMonitor) as usize - ptr as usize },
4usize,
concat!(
"Offset of field: ",
stringify!(tagMONITORINFO),
"::",
stringify!(rcMonitor)
)
);
assert_eq!(
unsafe { ::std::ptr::addr_of!((*ptr).rcWork) as usize - ptr as usize },
20usize,
concat!(
"Offset of field: ",
stringify!(tagMONITORINFO),
"::",
stringify!(rcWork)
)
);
assert_eq!(
unsafe { ::std::ptr::addr_of!((*ptr).dwFlags) as usize - ptr as usize },
36usize,
concat!(
"Offset of field: ",
stringify!(tagMONITORINFO),
"::",
stringify!(dwFlags)
)
);
}
pub type MONITORINFO = tagMONITORINFO;
pub type LPMONITORINFO = *mut tagMONITORINFO;
#[repr(C)]
#[repr(align(4))]
#[derive(Debug, Default, Copy, Clone)]
pub struct tagMONITORINFOEXA {
pub __bindgen_padding_0: [u8; 40usize],
pub szDevice: [CHAR; 32usize],
}
#[test]
fn bindgen_test_layout_tagMONITORINFOEXA() {
const UNINIT: ::std::mem::MaybeUninit<tagMONITORINFOEXA> = ::std::mem::MaybeUninit::uninit();
let ptr = UNINIT.as_ptr();
assert_eq!(
::std::mem::size_of::<tagMONITORINFOEXA>(),
72usize,
concat!("Size of: ", stringify!(tagMONITORINFOEXA))
);
assert_eq!(
::std::mem::align_of::<tagMONITORINFOEXA>(),
4usize,
concat!("Alignment of ", stringify!(tagMONITORINFOEXA))
);
assert_eq!(
unsafe { ::std::ptr::addr_of!((*ptr).szDevice) as usize - ptr as usize },
40usize,
concat!(
"Offset of field: ",
stringify!(tagMONITORINFOEXA),
"::",
stringify!(szDevice)
)
);
}
pub type MONITORINFOEXA = tagMONITORINFOEXA;
pub type LPMONITORINFOEXA = *mut tagMONITORINFOEXA;
Expected Results
I expected it to generate a default implementation successfully. This seems to be another regression of #1718/#1719 and #2082, where it fails to generate a valid Default when the array has more than the 32 entries (where rust itself generates a Default for <=32 entries).
Which rust version are you using? We have code to deal with this, see https://github.com/rust-lang/rust-bindgen/commit/a380678490b821201f10b861144b15bbe08694a2
Ah, so I couldn't repro this, but that's because for some reason --target=x86_64-pc-win32 is needed to repro:
./target/debug/bindgen --with-derive-default t.h -- --target=x86_64-pc-win32
Is the command I used to reproduce. It seems the MONITORINFO; line is kind of like a member, but it's unnamed and clang doesn't expose it as such... o.O
I think that limitation in rustc is mostly historical? https://github.com/rust-lang/rust/pull/124163 removes it.
@emilio
Which rust version are you using? We have code to deal with this, see https://github.com/rust-lang/rust-bindgen/commit/a380678490b821201f10b861144b15bbe08694a2
I'm able to repro on latest stable(stable-x86_64-pc-windows-msvc unchanged - rustc 1.77.2 (25ef9e3d8 2024-04-09)), beta(beta-x86_64-pc-windows-msvc updated - rustc 1.78.0-beta.7 (6fd191292 2024-04-12) (from rustc 1.78.0-beta.5 (9eff51035 2024-04-06))), and nightly(nightly-x86_64-pc-windows-msvc updated - rustc 1.79.0-nightly (e3181b091 2024-04-18) (from rustc 1.79.0-nightly (8b2459c1f 2024-04-09))). I'm assuming this is some sort of regression.
Ah, so I couldn't repro this, but that's because for some reason --target=x86_64-pc-win32 is needed to repro:
I am using x64 windows w/ msvc toolchain, so my native target is x86_64-pc-windows-msvc
I've also tried enabling clang's msvc compat, and it doesn't alter behavior here:
.clang_args([
"-fms-compatibility",
"-fms-extensions",
"-fdelayed-template-parsing",
])
@emilio looks like your proposed patch to rust was rejected. Can this continue to be handled by bindgen?
I think this issue is a bit deeper than just a missing Default implementation. If we had something like this:
// hello.c
typedef struct bar {
int *a[17];
} bar;
typedef struct foo {
bar;
int b;
} foo;
and ran bindgen hello.c --with-derive-default --no-layout-tests -- --target=x86_64-pc-windows-mvsc -fms-extensions you'd get:
/* automatically generated by rust-bindgen 0.69.4 */
#[repr(C)]
#[derive(Debug, Copy, Clone)]
pub struct bar {
pub a: [*mut ::std::os::raw::c_int; 17usize],
}
impl Default for bar {
fn default() -> Self {
let mut s = ::std::mem::MaybeUninit::<Self>::uninit();
unsafe {
::std::ptr::write_bytes(s.as_mut_ptr(), 0, 1);
s.assume_init()
}
}
}
#[repr(C)]
#[repr(align(8))]
#[derive(Debug, Default, Copy, Clone)]
pub struct foo {
pub __bindgen_padding_0: [u32; 34usize],
pub b: ::std::os::raw::c_int,
}
implementing Default for foo is most likely wrong as you'd end up with an array of null pointers. I guess this is just a symptom of clang exposing the anonymous struct inside foo as an opaque type instead of giving the proper information.
