ICE in non_zero_size_type, at rust/rust-gcc.cc:1895

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auto-reduced (treereduce-rust):

#[repr(C)]
union U {
    data: (),
}

extern "C" {
    static FOREIGN1: U; // OK

}

original:

#![allow(unused)]
#![deny(improper_ctypes)]

#[repr(C)]
union U {
    data: (),
}

union W {
    a: u8,
}

extern "C" {
    static FOREIGN1: U; // OK
    static FOREIGN2: W; //~ ERROR `extern` block uses type `W`
}

fn main() {}

Version information:

34b0a681598d52de442a0a21c3a7df20bf1485bc

Command:
crab1 -Warray-bounds -mtune=generic -march=x86-64 -O0 -L/lib/x86_64-linux-gnu -L/lib/../lib64 -L/usr/lib/x86_64-linux-gnu -L/usr/lib/../lib64 -frust-incomplete-and-experimental-compiler-do-not-use

Program output

crab1: internal compiler error: in non_zero_size_type, at rust/rust-gcc.cc:1895
0x8602fa Backend::non_zero_size_type(tree_node*)
	../../gcc/rust/rust-gcc.cc:1895
0xb44bc7 Backend::global_variable(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, tree_node*, bool, bool, bool, unsigned int)
	../../gcc/rust/rust-gcc.cc:1947
0xc75605 Rust::Compile::CompileExternItem::visit(Rust::HIR::ExternalStaticItem&)
	../../gcc/rust/backend/rust-compile-extern.h:75
0xfd63c6 Rust::Compile::CompileExternItem::compile(Rust::HIR::ExternalItem*, Rust::Compile::Context*, Rust::TyTy::BaseType*, bool, unsigned int)
	../../gcc/rust/backend/rust-compile-extern.h:41
0xfd63c6 Rust::Compile::CompileItem::visit(Rust::HIR::ExternBlock&)
	../../gcc/rust/backend/rust-compile-item.cc:288
0xc64994 Rust::Compile::CompileItem::compile(Rust::HIR::Item*, Rust::Compile::Context*, Rust::TyTy::BaseType*, unsigned int)
	../../gcc/rust/backend/rust-compile-item.h:37
0xc64994 Rust::Compile::CompileCrate::go()
	../../gcc/rust/backend/rust-compile.cc:48
0xc64a7b Rust::Compile::CompileCrate::Compile(Rust::HIR::Crate&, Rust::Compile::Context*)
	../../gcc/rust/backend/rust-compile.cc:41
0xc5c48b Rust::Session::compile_crate(char const*)
	../../gcc/rust/rust-session-manager.cc:733
Please submit a full bug report, with preprocessed source (by using -freport-bug).
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.

Reproduce the reduced Rust case with the command in the issue, then inspect non_zero_size_type and global_variable in rust/rust-gcc.cc around lines 1889-1901, along with CompileExternItem in rust/backend/rust-compile-extern.h. Done means the reduced case no longer triggers an internal compiler error and the original extern-static case reports the expected improper_ctypes error for W.

Written by the indexing model from the issue text.

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