ParseSyntaxError in wgpu-native

[kvark]

Repro steps on Linux:

git clone https://github.com/kvark/wgpu -b swap-chain
cd wgpu
RUST_BACKTRACE=1 make

Error:

thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: ParseSyntaxError { crate_name: "wgpu-native", src_path: "", error: Error { start_span: Span, end_span: Span, message: "expected one of: `for`, parentheses, `fn`, `unsafe`, `extern`, identifier, `::`, `<`, square brackets, `*`, `&`, `!`, `impl`, `_`, lifetime" } }', src/libcore/result.rs:997:5
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:39
   1: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:70
   2: std::panicking::default_hook::{{closure}}
             at src/libstd/sys_common/backtrace.rs:58
             at src/libstd/panicking.rs:200
   3: std::panicking::default_hook
             at src/libstd/panicking.rs:215
   4: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:478
   5: std::panicking::continue_panic_fmt
             at src/libstd/panicking.rs:385
   6: rust_begin_unwind
             at src/libstd/panicking.rs:312
   7: core::panicking::panic_fmt
             at src/libcore/panicking.rs:85
   8: core::result::unwrap_failed
             at /rustc/daa53a52a2667533d5fe59bfcc5b8614b79c3d31/src/libcore/macros.rs:16
   9: <core::result::Result<T, E>>::unwrap
             at /rustc/daa53a52a2667533d5fe59bfcc5b8614b79c3d31/src/libcore/result.rs:798
  10: wgpu_bindings::main
             at wgpu-bindings/src/main.rs:35
  11: std::rt::lang_start::{{closure}}
             at /rustc/daa53a52a2667533d5fe59bfcc5b8614b79c3d31/src/libstd/rt.rs:64
  12: std::panicking::try::do_call
             at src/libstd/rt.rs:49
             at src/libstd/panicking.rs:297
  13: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:92
  14: std::rt::lang_start_internal
             at src/libstd/panicking.rs:276
             at src/libstd/panic.rs:388
             at src/libstd/rt.rs:48
  15: std::rt::lang_start
             at /rustc/daa53a52a2667533d5fe59bfcc5b8614b79c3d31/src/libstd/rt.rs:64
  16: main
  17: __libc_start_main
  18: _start
             at ../sysdeps/x86_64/start.S:120

[grovesNL]

I investigated this a bit last night. To get source for parsing, cbindgen runs:

cargo rustc --lib --manifest-path /Users/josh/Projects/wgpu-native/wgpu-native/Cargo.toml -p wgpu-native:0.1.0 -- -Z unstable-options --pretty=expanded

But the output of this command doesn't compile in Rust, because it fails on the $:

https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=90fb57da21a6a9ef22088c29048bc568

So I don't really expect syn to parse this because it doesn't even compile. It would be useful if somebody could help clarify whether the issue related to the rustc macro expansion, syn, or cbindgen?

[emilio]

I would expect $crate to be expanded using --pretty=expanded the same way all the other macro $variables are expanded.

[grovesNL]

It seems related to rustc changing behavior for macro expansion between 2018-12-27-fb86d604b and 2018-12-28-60e825389 nightlies.

I have an example here which displays the difference in output https://gist.github.com/grovesNL/5d3ddc7b95c1939be26c64ba09f1ac2f

I also mentioned it on a PR which appears to be related rust-lang/rust#57155

[cathaysia]

if you print something in macro, then this error will be raised.