Incorrect Size when C++ std::string in struct

[JonBoyleCoding]

Hi, when trying to create bindings to a struct that contains a C++ std::string, the tests on those particular structs fail with an incorrect size.

I'm using bindgen version 0.54.0 and using clang version 10.0.0 provided via linuxbrew.

Is this something that:

• should work and it's a setup issue on my end?
• something that's not supported?
• something that I can continue using and not worry about?
• something that there is a decent workaround for?
• something I haven't thought of?

I would note the library I am wanting to use bindgen on isn't able to be changed.

Thanks

Input C/C++ Header

#ifndef BINDGEN_TEST_TEST_STRUCT_H
#define BINDGEN_TEST_TEST_STRUCT_H

#include <string>

struct JStructString {
    std::string mystring;
};

#endif //BINDGEN_TEST_TEST_STRUCT_H

Bindgen Invocation

    let bindings = bindgen::Builder::default()
        .header("test_struct.h")
        .clang_args(&["-x", "c++"])
        .whitelist_type("JStructString")
        .enable_cxx_namespaces()
        .parse_callbacks(Box::new(bindgen::CargoCallbacks))
        // Finish the builder and generate the bindings.
        .generate()
        // Unwrap the Result and panic on failure.
        .expect("Unable to generate bindings");

Actual Results

test root::__bindgen_test_layout_basic_string_open0_char_char_traits_open1_char_close1_allocator_open1_char_close1_close0_instantiation ... FAILED
test root::bindgen_test_layout_JStructString ... FAILED

failures:

---- root::__bindgen_test_layout_basic_string_open0_char_char_traits_open1_char_close1_allocator_open1_char_close1_close0_instantiation stdout ----
thread 'root::__bindgen_test_layout_basic_string_open0_char_char_traits_open1_char_close1_allocator_open1_char_close1_close0_instantiation' panicked at 'assertion failed: `(left == right)`
  left: `16`,
 right: `32`: Size of template specialization: root :: std :: basic_string < :: std :: os :: raw :: c_char >', /data1/Programming/bindgen_test/target/debug/build/bindgen_test-50b60b0d3abdf93c/out/bindings.rs:451:9
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.34/src/backtrace/libunwind.rs:88
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.34/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:47
   3: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:36
   4: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:200
   5: std::panicking::default_hook
             at src/libstd/panicking.rs:211
   6: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:477
   7: std::panicking::continue_panic_fmt
             at src/libstd/panicking.rs:384
   8: std::panicking::begin_panic_fmt
             at src/libstd/panicking.rs:339
   9: bindgen_test::root::__bindgen_test_layout_basic_string_open0_char_char_traits_open1_char_close1_allocator_open1_char_close1_close0_instantiation
             at ./target/debug/build/bindgen_test-50b60b0d3abdf93c/out/bindings.rs:451
  10: bindgen_test::root::__bindgen_test_layout_basic_string_open0_char_char_traits_open1_char_close1_allocator_open1_char_close1_close0_instantiation::{{closure}}
             at ./target/debug/build/bindgen_test-50b60b0d3abdf93c/out/bindings.rs:449
  11: core::ops::function::FnOnce::call_once
             at /rustc/625451e376bb2e5283fc4741caa0a3e8a2ca4d54/src/libcore/ops/function.rs:235
  12: <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once
             at /rustc/625451e376bb2e5283fc4741caa0a3e8a2ca4d54/src/liballoc/boxed.rs:787
  13: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:80
  14: std::panicking::try
             at /rustc/625451e376bb2e5283fc4741caa0a3e8a2ca4d54/src/libstd/panicking.rs:275
  15: std::panic::catch_unwind
             at /rustc/625451e376bb2e5283fc4741caa0a3e8a2ca4d54/src/libstd/panic.rs:394
  16: test::run_test::run_test_inner::{{closure}}
             at src/libtest/lib.rs:1408
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

---- root::bindgen_test_layout_JStructString stdout ----
thread 'root::bindgen_test_layout_JStructString' panicked at 'assertion failed: `(left == right)`
  left: `16`,
 right: `32`: Size of: JStructString', /data1/Programming/bindgen_test/target/debug/build/bindgen_test-50b60b0d3abdf93c/out/bindings.rs:427:9
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.34/src/backtrace/libunwind.rs:88
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.34/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:47
   3: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:36
   4: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:200
   5: std::panicking::default_hook
             at src/libstd/panicking.rs:211
   6: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:477
   7: std::panicking::continue_panic_fmt
             at src/libstd/panicking.rs:384
   8: std::panicking::begin_panic_fmt
             at src/libstd/panicking.rs:339
   9: bindgen_test::root::bindgen_test_layout_JStructString
             at ./target/debug/build/bindgen_test-50b60b0d3abdf93c/out/bindings.rs:427
  10: bindgen_test::root::bindgen_test_layout_JStructString::{{closure}}
             at ./target/debug/build/bindgen_test-50b60b0d3abdf93c/out/bindings.rs:426
  11: core::ops::function::FnOnce::call_once
             at /rustc/625451e376bb2e5283fc4741caa0a3e8a2ca4d54/src/libcore/ops/function.rs:235
  12: <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once
             at /rustc/625451e376bb2e5283fc4741caa0a3e8a2ca4d54/src/liballoc/boxed.rs:787
  13: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:80
  14: std::panicking::try
             at /rustc/625451e376bb2e5283fc4741caa0a3e8a2ca4d54/src/libstd/panicking.rs:275
  15: std::panic::catch_unwind
             at /rustc/625451e376bb2e5283fc4741caa0a3e8a2ca4d54/src/libstd/panic.rs:394
  16: test::run_test::run_test_inner::{{closure}}
             at src/libtest/lib.rs:1408
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

[emilio]

Yeah, there are known issues with the STL (which is very unfortunate, I know). Generally it's recommended to mark the stl as blacklisted or opaque, so that the types have the right layout :/

[emilio]

Closing as a duplicate of #738.