ICE when using cfg_if and defining a macro with macro_rules twice.

[theypsilon]

Compiler crash when using cfg_if and defining a macro with macro_rules twice.

I tried this code:

// file lib.rs
#[macro_use]
extern crate cfg_if;

mod test;
mod foo;

// file foo.rs
cfg_if! {
    if #[cfg(unix)] {
#[macro_export]
macro_rules! foo {
    ( $x:expr, $y:expr ) => {
        ($x + $y)
    };
}
    }
}

#[macro_export]
macro_rules! foo {
    ( $x:expr, $y:expr ) => {
        ($x + $y)
    };
}

//file test.rs
use crate::foo;

#[test]
fn test_true() {
    assert_eq!(foo!(1, 2), 3);
}

In a repo: https://github.com/theypsilon/rust-bug-crash-cfg-if-macro

I expected to see this happen:

error: a macro namedfoohas already been exported

Instead, this happened:

error: internal compiler error: unexpected panic

Meta

rustc --version --verbose:

rustc 1.32.0-beta.1 (eb53c1039 2018-12-05)
binary: rustc
commit-hash: eb53c1039300a8bc8f8e4b29659ddc80b1e81b68
commit-date: 2018-12-05
host: x86_64-unknown-linux-gnu
release: 1.32.0-beta.1
LLVM version: 8.0

Backtrace:

   Compiling rust-bug v0.1.0 (/mnt/c/Users/Jose/Documents/Workspace/rust-bug)
thread 'rustc' panicked at 'src/librustc_resolve/resolve_imports.rs:941: inconsistent resolution for an import', src/librustc/util/bug.rs:47:26
thread 'rustc' panicked at 'src/librustc_resolve/resolve_imports.rs:941: inconsistent resolution for an import', src/librustc/util/bug.rs:47:26
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:71
   2: std::panicking::default_hook::{{closure}}
             at src/libstd/sys_common/backtrace.rs:59
             at src/libstd/panicking.rs:211
   3: std::panicking::default_hook
             at src/libstd/panicking.rs:227
   4: rustc::util::common::panic_hook
   5: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:495
   6: std::panicking::begin_panic
   7: rustc::util::bug::opt_span_bug_fmt::{{closure}}
   8: rustc::ty::context::tls::with_opt::{{closure}}
   9: rustc::ty::context::tls::with_context_opt
  10: rustc::ty::context::tls::with_opt
  11: rustc::util::bug::opt_span_bug_fmt
  12: rustc::util::bug::span_bug_fmt
  13: rustc_resolve::resolve_imports::ImportResolver::finalize_import::{{closure}}
  14: rustc_resolve::resolve_imports::ImportResolver::finalize_imports
  15: rustc_resolve::Resolver::resolve_crate
  16: rustc::util::common::time
  17: rustc_driver::driver::phase_2_configure_and_expand
  18: rustc_driver::driver::compile_input
  19: rustc_driver::run_compiler_with_pool
  20: <scoped_tls::ScopedKey<T>>::set
  21: rustc_driver::run_compiler
  22: rustc_driver::monitor::{{closure}}
  23: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:102
  24: <F as alloc::boxed::FnBox<A>>::call_box
  25: std::sys::unix::thread::Thread::new::thread_start
             at /rustc/eb53c1039300a8bc8f8e4b29659ddc80b1e81b68/src/liballoc/boxed.rs:683
             at src/libstd/sys_common/thread.rs:24
             at src/libstd/sys/unix/thread.rs:90
  26: start_thread
  27: __clone
query stack during panic:
end of query stack

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 1.32.0-beta.1 (eb53c1039 2018-12-05) running on x86_64-unknown-linux-gnu

note: compiler flags: -C debuginfo=2 -C incremental --crate-type lib

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

error: Could not compile `rust-bug`.
warning: build failed, waiting for other jobs to finish...
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:71
   2: std::panicking::default_hook::{{closure}}
             at src/libstd/sys_common/backtrace.rs:59
             at src/libstd/panicking.rs:211
   3: std::panicking::default_hook
             at src/libstd/panicking.rs:227
   4: rustc::util::common::panic_hook
   5: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:495
   6: std::panicking::begin_panic
   7: rustc::util::bug::opt_span_bug_fmt::{{closure}}
   8: rustc::ty::context::tls::with_opt::{{closure}}
   9: rustc::ty::context::tls::with_context_opt
  10: rustc::ty::context::tls::with_opt
  11: rustc::util::bug::opt_span_bug_fmt
  12: rustc::util::bug::span_bug_fmt
  13: rustc_resolve::resolve_imports::ImportResolver::finalize_import::{{closure}}
  14: rustc_resolve::resolve_imports::ImportResolver::finalize_imports
  15: rustc_resolve::Resolver::resolve_crate
  16: rustc::util::common::time
  17: rustc_driver::driver::phase_2_configure_and_expand
  18: rustc_driver::driver::compile_input
  19: rustc_driver::run_compiler_with_pool
  20: <scoped_tls::ScopedKey<T>>::set
  21: rustc_driver::run_compiler
  22: rustc_driver::monitor::{{closure}}
  23: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:102
  24: <F as alloc::boxed::FnBox<A>>::call_box
  25: std::sys::unix::thread::Thread::new::thread_start
             at /rustc/eb53c1039300a8bc8f8e4b29659ddc80b1e81b68/src/liballoc/boxed.rs:683
             at src/libstd/sys_common/thread.rs:24
             at src/libstd/sys/unix/thread.rs:90
  26: start_thread
  27: __clone
query stack during panic:
end of query stack

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 1.32.0-beta.1 (eb53c1039 2018-12-05) running on x86_64-unknown-linux-gnu

note: compiler flags: -C debuginfo=2 -C incremental

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

error: Could not compile `rust-bug`.

To learn more, run the command again with --verbose.

[jethrogb]

Regression from stable to stable (works in 1.30).

Reduced test case:

#![allow(duplicate_macro_exports)]
macro_rules! a {
    ( @1 $i:item ) => {
        a! { @2 $i }
    };
    ( @2 $i:item ) => {
        $i
    };
}
mod b {
    a! {
        @1
        #[macro_export]
        macro_rules! b { () => () }
    }
    #[macro_export]
    macro_rules! b { () => () }
}
mod c {
    use crate::b;
}

[petrochenkov]

#![allow(duplicate_macro_exports)] mode is implemented on best effort basis, generally unsupported and will be removed in some time.

[petrochenkov]

Ah, I see, the original issue doesn't have it.
I'll investigate.

[Centril]

Reproducer in #58490 (comment) no longer ICEs.