ICE when path-exporting and using a macro-generated macro_rules! macro

[danielhenrymantilla]

The objective was to be able to feature some macro which would yield a $self:ident parameter with the def-site of a there-defined macro macro so as to mock the suggested $self parameter on macros.

Code

#![feature(decl_macro, trace_macros)]

// trace_macros!(true); /* to debug: the expansion works successfully */

module::recurse! { 1 1 1 }

pub mod module {
    pub(super) use private::recurse;

    mod private {
        macro __helper__ ([$dol:tt] $exported_name:ident) {
            macro_rules! $exported_name {(
                $dol(1 $dol($rest:tt)*)?
            ) => (
                $dol(
                //  the idea is for this to have def-site hygiene here
                //  vvvv
                    self::$exported_name! { $dol($rest)* }
                )?
            )} pub(crate) use $exported_name;
        }
        __helper__! { [$] recurse }
    }
}

• Playground with this simpler example

• Original code & Playground

Meta

rustc --version --verbose:

rustc 1.52.0-nightly (fe1bf8e05 2021-02-23)
binary: rustc
commit-hash: fe1bf8e05c39bdcc73fc09e246b7209444e389bc
commit-date: 2021-02-23
host: x86_64-apple-darwin
release: 1.52.0-nightly
LLVM version: 11.0.1

Error output

error: internal compiler error: expansion entered force mode without producing any errors
  --> src/lib.rs:29:1
   |
29 | outer::recurse! { 1 1 1 }
   | ^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: delayed at compiler/rustc_expand/src/expand.rs:447:34

thread 'rustc' panicked at 'no errors encountered even though `delay_span_bug` issued', compiler/rustc_errors/src/lib.rs:1012:13
note: run with `RUST_BACKTRACE=1` environment variable to display 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/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.52.0-nightly (fe1bf8e05 2021-02-23) running on x86_64-apple-darwin

note: compiler flags: -C embed-bitcode=no -C debuginfo=2 -C incremental --crate-type lib

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

query stack during panic:
end of query stack

Backtrace

stack backtrace:
   …
   5:        0x1020a36a8 - rustc_driver::report_ice::hcdbc085c8141570d
   …
  10:        0x1093532ab - std::panicking::begin_panic_fmt::hba7ec5d426758edb
  11:        0x10600ee16 - rustc_errors::HandlerInner::flush_delayed::h161e3beabf00546a
  12:        0x10600b10b - <rustc_errors::HandlerInner as core::ops::drop::Drop>::drop::hde0ac14a81f422db
  13:        0x1020ab07d - core::ptr::drop_in_place<rustc_session::parse::ParseSess>::h0cb46aa2558b566b
  14:        0x1020afda8 - <alloc::rc::Rc<T> as core::ops::drop::Drop>::drop::h5a4e1115e34fca86
  15:        0x102110835 - core::ptr::drop_in_place<rustc_interface::interface::Compiler>::hbf9fc4b317f8829b
  16:        0x10210cd08 - rustc_span::with_source_map::hdc8b53d5836d0f69
  17:        0x1020ba394 - rustc_interface::interface::create_compiler_and_run::h2e5f4f156384205a
  18:        0x1020b2db9 - scoped_tls::ScopedKey<T>::set::hb5d8ea6cc29ec656
  19:        0x1020b4101 - std::sys_common::backtrace::__rust_begin_short_backtrace::h316820ab0a243dd5
  20:        0x1020d85e9 - core::ops::function::FnOnce::call_once{{vtable.shim}}::h0dcd073e2532982e
  21:        0x1092d897d - std::sys::unix::thread::Thread::new::thread_start::h4da435b3f287e7dd
  22:     0x7fff20323950 - __pthread_start

cc @Aaron1011

[danielhenrymantilla]

I have found something that may be interesting. The following ICEs:

#![feature(decl_macro)]

pub mod module {
    mod private {
        __helper__! { [$] recurse }
    
        macro __helper__ ([$dol:tt] $exported_name:ident) {
            macro_rules! $exported_name {() => ()}
            pub(crate) use $exported_name;
        }
            // pub(crate) use recurse;
    }
    pub(super) use private::recurse;
}

module::recurse!();

but the following does not:

#![feature(decl_macro)]

pub mod module {
    mod private {
        __helper__! { [$] recurse }
    
        macro __helper__ ([$dol:tt] $exported_name:ident) {
            macro_rules! $exported_name {() => ()}
            // pub(crate) use $exported_name;
        }
            pub(crate) use recurse;
    }
    pub(super) use private::recurse;
}

module::recurse!();

---

        macro __helper__ ([$dol:tt] $exported_name:ident) {
            macro_rules! $exported_name {() => ()}
+           pub(crate) use $exported_name;
        }
-           pub(crate) use recurse;

[Alexendoo]

No longer ICEs since #108729

[JohnTitor]

Triage: Closing as #108729 should have a regression test covering this case.