ICE "attempting to document proc-macro re-export"

[Bobo1239]

Running cargo doc on synstructure 0.6.1 (which is transitively depended on by the latest failure_derive release) fails with an ICE.
Repro:

git clone git@github.com:mystor/synstructure
cd synstructure
git checkout 41cd679439568ecd32acd46569ad89c36239af86
cargo doc

thread '<unnamed>' panicked at 'attempting to document proc-macro re-export', librustdoc/clean/inline.rs:474:39
note: Run with `RUST_BACKTRACE=1` for a backtrace.
error: internal compiler error: unexpected panic
note: the compiler unexpectedly panicked. this is a bug.
note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports
note: rustc 1.29.0-nightly (e06c87544 2018-07-06) running on x86_64-unknown-linux-gnu
error: Could not document `synstructure`.
Caused by:
  process didn't exit successfully: `rustdoc --crate-name synstructure src/lib.rs -o /home/bobo1239/Development/Rust/synstructure/target/doc -L dependency=/home/bobo1239/Development/Rust/synstructure/target/debug/deps --extern quote=/home/bobo1239/Development/Rust/synstructure/target/debug/deps/libquote-60e72af659eb759e.rmeta --extern syn=/home/bobo1239/Development/Rust/synstructure/target/debug/deps/libsyn-8c0b65e753b5dc70.rmeta` (exit code: 101)

Meta

rustc --version --verbose:

rustc 1.29.0-nightly (e06c87544 2018-07-06)
binary: rustc
commit-hash: e06c875442e91cc2c597135d1e807a69e73eee26
commit-date: 2018-07-06
host: x86_64-unknown-linux-gnu
release: 1.29.0-nightly
LLVM version: 6.0

Backtrace:

thread '<unnamed>' panicked at 'attempting to document proc-macro re-export', librustdoc/clean/inline.rs:474:39
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::print
             at libstd/sys_common/backtrace.rs:71
             at libstd/sys_common/backtrace.rs:59
   2: std::panicking::default_hook::{{closure}}
             at libstd/panicking.rs:211
   3: std::panicking::default_hook
             at libstd/panicking.rs:227
   4: std::panicking::rust_panic_with_hook
             at libstd/panicking.rs:475
   5: std::panicking::begin_panic
             at /checkout/src/libstd/panicking.rs:409
   6: rustdoc::clean::inline::try_inline
             at librustdoc/clean/inline.rs:474
             at librustdoc/clean/inline.rs:107
   7: rustdoc::clean::inline::build_module::fill_in
             at librustdoc/clean/inline.rs:442
   8: <rustdoc::doctree::Import as rustdoc::clean::Clean<alloc::vec::Vec<rustdoc::clean::Item>>>::clean
             at librustdoc/clean/inline.rs:427
             at librustdoc/clean/inline.rs:134
             at librustdoc/clean/mod.rs:3938
   9: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T, I>>::spec_extend
             at librustdoc/clean/mod.rs:590
             at /checkout/src/libcore/ops/function.rs:271
             at /checkout/src/libcore/option.rs:414
             at /checkout/src/libcore/iter/mod.rs:1392
             at /checkout/src/libcore/iter/mod.rs:2684
             at /checkout/src/libcore/iter/mod.rs:2521
             at /checkout/src/liballoc/vec.rs:1963
             at /checkout/src/liballoc/vec.rs:1860
  10: <rustdoc::doctree::Module as rustdoc::clean::Clean<rustdoc::clean::Item>>::clean
             at /checkout/src/liballoc/vec.rs:1824
             at librustdoc/clean/mod.rs:590
  11: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T, I>>::spec_extend
             at librustdoc/clean/mod.rs:596
             at /checkout/src/libcore/ops/function.rs:271
             at /checkout/src/libcore/option.rs:414
             at /checkout/src/libcore/iter/mod.rs:1392
             at /checkout/src/liballoc/vec.rs:1886
  12: <rustdoc::doctree::Module as rustdoc::clean::Clean<rustdoc::clean::Item>>::clean
             at /checkout/src/liballoc/vec.rs:1824
             at librustdoc/clean/mod.rs:596
  13: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T, I>>::spec_extend
             at librustdoc/clean/mod.rs:596
             at /checkout/src/libcore/ops/function.rs:271
             at /checkout/src/libcore/option.rs:414
             at /checkout/src/libcore/iter/mod.rs:1392
             at /checkout/src/liballoc/vec.rs:1886
  14: <rustdoc::doctree::Module as rustdoc::clean::Clean<rustdoc::clean::Item>>::clean
             at /checkout/src/liballoc/vec.rs:1824
             at librustdoc/clean/mod.rs:596
  15: <rustdoc::visit_ast::RustdocVisitor<'a, 'tcx, 'rcx> as rustdoc::clean::Clean<rustdoc::clean::Crate>>::clean
             at librustdoc/clean/mod.rs:167
  16: rustdoc::core::run_core::{{closure}}::{{closure}}
             at librustdoc/core.rs:363
  17: rustc::ty::context::tls::enter_context
             at /checkout/src/librustc_driver/driver.rs:1315
             at /checkout/src/librustc/ty/context.rs:1862
             at /checkout/src/librustc/ty/context.rs:1830
             at /checkout/src/librustc/ty/context.rs:1769
             at /checkout/src/librustc/ty/context.rs:1829
  18: <std::thread::local::LocalKey<T>>::with
             at /checkout/src/librustc/ty/context.rs:1861
             at /checkout/src/librustc/ty/context.rs:1819
             at /checkout/src/libstd/thread/local.rs:294
             at /checkout/src/libstd/thread/local.rs:248
             at /checkout/src/librustc/ty/context.rs:1811
             at /checkout/src/libstd/thread/local.rs:294
             at /checkout/src/libstd/thread/local.rs:248
  19: rustc::ty::context::TyCtxt::create_and_enter
             at /checkout/src/librustc/ty/context.rs:1803
             at /checkout/src/librustc/ty/context.rs:1841
             at /checkout/src/librustc/ty/context.rs:1186
  20: rustc_driver::driver::phase_3_run_analysis_passes
             at /checkout/src/librustc_driver/driver.rs:1227
  21: <scoped_tls::ScopedKey<T>>::set
             at librustdoc/core.rs:308
             at /checkout/src/librustc_driver/driver.rs:73
             at /cargo/registry/src/github.com-1ecc6299db9ec823/scoped-tls-0.1.2/src/lib.rs:155
  22: rustdoc::core::run_core
             at /checkout/src/librustc_driver/driver.rs:72
             at librustdoc/core.rs:236
  23: <scoped_tls::ScopedKey<T>>::set
             at librustdoc/lib.rs:674
             at /cargo/registry/src/github.com-1ecc6299db9ec823/scoped-tls-0.1.2/src/lib.rs:155
             at /checkout/src/libsyntax/lib.rs:98
             at /cargo/registry/src/github.com-1ecc6299db9ec823/scoped-tls-0.1.2/src/lib.rs:155
  24: syntax::with_globals
             at /checkout/src/libsyntax/lib.rs:97
  25: <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
             at librustdoc/lib.rs:670
             at /checkout/src/librustc_driver/lib.rs:1613
             at /checkout/src/libstd/panic.rs:313
  26: std::panicking::try::do_call
             at /checkout/src/libstd/panicking.rs:310
  27: __rust_maybe_catch_panic
             at libpanic_unwind/lib.rs:105
  28: rustc_driver::monitor
             at /checkout/src/libstd/panicking.rs:289
             at /checkout/src/libstd/panic.rs:392
             at /checkout/src/librustc_driver/lib.rs:1545
             at /checkout/src/librustc_driver/lib.rs:1612
  29: rustdoc::rust_input
             at librustdoc/lib.rs:670
  30: rustdoc::main_args
             at librustdoc/lib.rs:590
             at librustdoc/lib.rs:545
  31: <scoped_tls::ScopedKey<T>>::set
             at librustdoc/lib.rs:116
             at /checkout/src/libcore/option.rs:414
             at librustdoc/lib.rs:116
             at /cargo/registry/src/github.com-1ecc6299db9ec823/scoped-tls-0.1.2/src/lib.rs:155
             at /checkout/src/libsyntax/lib.rs:98
             at /cargo/registry/src/github.com-1ecc6299db9ec823/scoped-tls-0.1.2/src/lib.rs:155
  32: syntax::with_globals
             at /checkout/src/libsyntax/lib.rs:97
  33: std::panicking::try::do_call
             at /checkout/src/libstd/thread/mod.rs:409
             at /checkout/src/libstd/panic.rs:313
             at /checkout/src/libstd/panicking.rs:310
  34: __rust_maybe_catch_panic
             at libpanic_unwind/lib.rs:105
  35: <F as alloc::boxed::FnBox<A>>::call_box
             at /checkout/src/libstd/panicking.rs:289
             at /checkout/src/libstd/panic.rs:392
             at /checkout/src/libstd/thread/mod.rs:408
             at /checkout/src/liballoc/boxed.rs:640
  36: std::sys_common::thread::start_thread
             at /checkout/src/liballoc/boxed.rs:650
             at libstd/sys_common/thread.rs:24
  37: std::sys::unix::thread::Thread::new::thread_start
             at libstd/sys/unix/thread.rs:90
  38: start_thread
  39: clone

[ollie27]

This was caused by #51611. It used to be a silent failure but was changed into an ICE. cc. @QuietMisdreavus

[LunaBorowska]

Happens for me as well: https://gitlab.com/KonradBorowski/result_float/-/jobs/81199544

[QuietMisdreavus]

Minimal reproduction:

extern crate proc_macro;

pub use proc_macro::*;

...although it depends on quote!() being both a bang macro and a proc-macro. I have a patch ready to ignore this, but i dunno how to reduce it to a test that doesn't depend on libproc_macro's quote!().