ICE in insert_ast_item when the same crate is declared twice under different names

Summary

Declaring the same crate twice under different names is legal Rust, but gccrs ICEs during HIR lowering. Found while working on #4679; it looks related but is a distinct problem, so filing separately.

Reproducer

foo.rs:

#![feature(no_core)]
#![no_core]

v4.rs:

#![feature(no_core)]
#![no_core]

extern crate foo;
extern crate foo as bar;

Build foo to metadata first, then compile v4.rs against it:

gccrs -frust-incomplete-and-experimental-compiler-do-not-use \
      -frust-crate=foo -frust-crate-type=rlib \
      -frust-metadata-output=foo.rox -c foo.rs -o foo.o

gccrs -frust-incomplete-and-experimental-compiler-do-not-use \
      -frust-crate-attr=no_core -frust-crate-attr='feature(no_core)' \
      -frust-extern=foo=foo.rox -c v4.rs

The bare snippet on its own won't reproduce it: without a real crate it fails
at "failed to locate crate" before reaching lowering.

Does the code make use of any (1.49) nightly feature ?

• Nightly

Godbolt link

No response

Actual behavior

crab1: internal compiler error: in insert_ast_item, at rust/util/rust-hir-map.cc:1264
0x2bace8b internal_error(char const*, ...)
	../../gccrs/gcc/diagnostic-global-context.cc:787
0xb55fab fancy_abort(char const*, int, char const*)
	../../gccrs/gcc/diagnostics/context.cc:1813
0x911607 Rust::Analysis::Mappings::insert_ast_item(Rust::AST::Item*)
	../../gccrs/gcc/rust/util/rust-hir-map.cc:1264
0xe19a1e Rust::HIR::ASTLoweringItem::translate(Rust::AST::Item&)
	../../gccrs/gcc/rust/hir/rust-ast-lower-item.cc:47
0xe0b9d7 Rust::HIR::ASTLowering::go()
	../../gccrs/gcc/rust/hir/rust-ast-lower.cc:79
0xe0be55 Rust::HIR::ASTLowering::Resolve(Rust::AST::Crate&)
	../../gccrs/gcc/rust/hir/rust-ast-lower.cc:69
0xe19678 Rust::HIR::ASTLoweringItem::visit(Rust::AST::ExternCrate&)
	../../gccrs/gcc/rust/hir/rust-ast-lower-item.cc:800
0xe1999b Rust::HIR::ASTLoweringItem::translate(Rust::AST::Item&)
	../../gccrs/gcc/rust/hir/rust-ast-lower-item.cc:38
0xe0b9d7 Rust::HIR::ASTLowering::go()
	../../gccrs/gcc/rust/hir/rust-ast-lower.cc:79
0xe0be55 Rust::HIR::ASTLowering::Resolve(Rust::AST::Crate&)
	../../gccrs/gcc/rust/hir/rust-ast-lower.cc:69
0xd3b90e Rust::Session::compile_crate(char const*)
	../../gccrs/gcc/rust/rust-session-manager.cc:785
/home/utkuputku/gsoc/gccrs-build/gcc/crab1 v4.rs -quiet -dumpbase v4.rs -dumpbase-ext .rs -mtune=generic -march=x86-64 -frust-incomplete-and-experimental-compiler-do-not-use -frust-crate-attr=no_core -frust-crate-attr=feature(no_core) -frust-extern=foo=foo.rox -L/home/utkuputku/gsoc/gccrs-build/gcc -L/lib/x86_64-linux-gnu -L/lib/../lib64 -L/usr/lib/x86_64-linux-gnu -L/usr/lib/../lib64 -L/lib -L/usr/lib -o /tmp/ccYD1yS6.s

ASTLoweringItem::visit (AST::ExternCrate &) at rust-ast-lower-item.cc:800
calls ASTLowering::Resolve on the referenced crate with no guard against it
having already been lowered. Both items name the same crate, so it gets
lowered twice, and the second pass re-inserts NodeIds already present in
ast_item_mappings, tripping the assert at rust-hir-map.cc:1264.

This appears keyed on crate identity rather than binding name, which fits what
I see: extern crate foo; extern crate foo; hits the same assert, while two
items naming different crates do not.

Expected behavior

This should compile. Binding one crate under two names is legal Rust; rustc
1.95.0 accepts it and produces a binary.

GCC Version

gccrs (GCC) 17.0.0 20260630 (experimental)

Start with the reproducer commands in the issue, then inspect ASTLoweringItem::visit for AST::ExternCrate in rust-ast-lower-item.cc:800 and the assertion in rust-hir-map.cc:1264. Verify behavior with two extern crate declarations naming the same crate and with different crates. Done means the duplicate-name case compiles without an ICE and preserves the expected crate bindings.