Declarative macros can create infinite glob import cycles

[matthewjasper]

The following code results in A being cyclicly glob imported from x into y and back with a different identifier (it gains a new mark on each import).

#![feature(decl_macro)]

pub macro m($i:ident, $j:ident) {
    mod $i {
        pub use crate::$j::*;
        pub struct A;
    }
}

m!(x, y);
m!(y, x);

Backtrace

thread 'rustc' panicked at 'already borrowed: BorrowMutError', src/libcore/result.rs:1165:5
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.37/src/backtrace/libunwind.rs:88
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.37/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print_fmt
             at src/libstd/sys_common/backtrace.rs:76
   3: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
             at src/libstd/sys_common/backtrace.rs:60
   4: core::fmt::write
             at src/libcore/fmt/mod.rs:1030
   5: std::io::Write::write_fmt
             at src/libstd/io/mod.rs:1412
   6: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:64
   7: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:49
   8: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:196
   9: std::panicking::default_hook
             at src/libstd/panicking.rs:210
  10: rustc_driver::report_ice
  11: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:477
  12: std::panicking::continue_panic_fmt
             at src/libstd/panicking.rs:380
  13: rust_begin_unwind
             at src/libstd/panicking.rs:307
  14: core::panicking::panic_fmt
             at src/libcore/panicking.rs:85
  15: core::result::unwrap_failed
             at src/libcore/result.rs:1165
  16: rustc_resolve::resolve_imports::<impl rustc_resolve::Resolver>::try_define
  17: rustc_resolve::resolve_imports::<impl rustc_resolve::Resolver>::try_define
  18: rustc_resolve::resolve_imports::<impl rustc_resolve::Resolver>::try_define
  19: rustc_resolve::resolve_imports::ImportResolver::resolve_imports
  20: rustc_resolve::macros::<impl syntax::ext::base::Resolver for rustc_resolve::Resolver>::resolve_imports
  21: syntax::ext::expand::MacroExpander::fully_expand_fragment
  22: syntax::ext::expand::MacroExpander::expand_crate
  23: rustc_interface::passes::configure_and_expand_inner::{{closure}}
  24: rustc::util::common::time
  25: rustc_interface::passes::configure_and_expand_inner
  26: rustc_interface::passes::configure_and_expand::{{closure}}
  27: rustc_data_structures::box_region::PinnedGenerator<I,A,R>::new
  28: rustc_interface::passes::configure_and_expand
  29: rustc_interface::queries::Query<T>::compute
  30: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::expansion
  31: rustc_interface::interface::run_compiler_in_existing_thread_pool
  32: std::thread::local::LocalKey<T>::with
  33: scoped_tls::ScopedKey<T>::set
  34: syntax::with_globals
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose 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 1.39.0-nightly (6ef275e6c 2019-09-24) running on x86_64-unknown-linux-gnu

note: compiler flags: -C codegen-units=1 -C debuginfo=2 --crate-type lib

note: some of the compiler flags provided by cargo are hidden

[JohnTitor]

Fixed on the latest nightly, marking as E-needs-test
@rustbot labels: +E-needs-test