Bad clang flags results in "libclang: crash detected during parsing" but we can report better errors than this

Hello, looks like I have some kind of infrastructure problem.

Every time I invoke bindgen it complains in the same way, i.e. it does not depend on the input file:

$ RUST_BACKTRACE=full bindgen Input.h  -- -x  
libclang: crash detected during parsing: {
  'source_filename' : ''
  'command_line_args' : ['-x', '-isystem', '/usr/bin/../lib/gcc/x86_64-linux-gnu/6.2.0/../../../../include/c++/6.2.0', '-isystem', '/usr/bin/../lib/gcc/x86_64-linux-gnu/6.2.0/../../../../include/x86_64-linux-gnu/c++/6.2.0', '-isystem', '/usr/bin/../lib/gcc/x86_64-linux-gnu/6.2.0/../../../../include/c++/6.2.0/backward', '-isystem', '/usr/local/include', '-isystem', '/usr/lib/llvm-3.9/bin/../lib/clang/3.9.0/include', '-isystem', '/usr/include/x86_64-linux-gnu', '-isystem', '/usr/include', 'Input.h'],
  'unsaved_files' : [],
  'options' : 1,
}
thread 'main' panicked at 'TranslationUnit::parse', /checkout/src/libcore/option.rs:794
stack backtrace:
   0:     0x559fa4225c83 - std::sys::imp::backtrace::tracing::imp::unwind_backtrace::h0c49f46a3545f908
                               at /checkout/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1:     0x559fa4221fe4 - std::sys_common::backtrace::_print::hcef39a9816714c4c
                               at /checkout/src/libstd/sys_common/backtrace.rs:71
   2:     0x559fa4229837 - std::panicking::default_hook::{{closure}}::h7c3c94835e02f846
                               at /checkout/src/libstd/sys_common/backtrace.rs:60
                               at /checkout/src/libstd/panicking.rs:355
   3:     0x559fa42293bb - std::panicking::default_hook::h0bf7bc3112fb107d
                               at /checkout/src/libstd/panicking.rs:371
   4:     0x559fa4229d0b - std::panicking::rust_panic_with_hook::ha27630c950090fec
                               at /checkout/src/libstd/panicking.rs:549
   5:     0x559fa4229be4 - std::panicking::begin_panic::heb97fa3158b71158
                               at /checkout/src/libstd/panicking.rs:511
   6:     0x559fa4229b19 - std::panicking::begin_panic_fmt::h8144403278d84748
                               at /checkout/src/libstd/panicking.rs:495
   7:     0x559fa4229aa7 - rust_begin_unwind
                               at /checkout/src/libstd/panicking.rs:471
   8:     0x559fa425534d - core::panicking::panic_fmt::h3b0cca53e68f9654
                               at /checkout/src/libcore/panicking.rs:69
   9:     0x559fa42553dd - core::option::expect_failed::h7b11713803917d42
                               at /checkout/src/libcore/option.rs:794
  10:     0x559fa3f1b746 - bindgen::ir::context::BindgenContext::new::ha61e71dda9b6b1fd
  11:     0x559fa3f398d8 - bindgen::Bindings::generate::h3172c41878a7aaea
  12:     0x559fa3f390f4 - bindgen::Builder::generate::hb35b757c0afec17a
  13:     0x559fa3e97b95 - std::panicking::try::do_call::h49c85f7e91ad7731
  14:     0x559fa4230b8a - __rust_maybe_catch_panic
                               at /checkout/src/libpanic_unwind/lib.rs:98
  15:     0x559fa3ebb434 - bindgen::main::h9f17fa3fe1757820
  16:     0x559fa4229a05 - std::panicking::try::do_call::h689a21caeeef92aa
                               at /checkout/src/libcore/ops.rs:2606
                               at /checkout/src/libstd/panicking.rs:454
  17:     0x559fa4230b8a - __rust_maybe_catch_panic
                               at /checkout/src/libpanic_unwind/lib.rs:98
  18:     0x559fa422a4aa - std::rt::lang_start::hf63d494cb7dd034c
                               at /checkout/src/libstd/panicking.rs:433
                               at /checkout/src/libstd/panic.rs:361
                               at /checkout/src/libstd/rt.rs:57
  19:     0x7f8fcccd33f0 - __libc_start_main
  20:     0x559fa3e96259 - _start
  21:                0x0 - <unknown>

My versions are:

• Kubuntu 16.10
• libclang 3.9 (installed as stated in README)
• bindgen 0.22.1 (installed using cargo)

Hope this helps.

Start at bindgen::ir::context::BindgenContext::new, identified in the stack trace, and reproduce the CLI invocation with the invalid -x flag. Trace how the TranslationUnit parse failure is handled and add coverage for this command-line case. Done means invalid clang flags produce a useful error instead of the reported panic.