[gcc r17-2233] gccrs: Fix ICE when trying to resolve const expr

https://gcc.gnu.org/g:3541e0be7cab2af23dc45757015f2bcdda93f9dc

commit r17-2233-g3541e0be7cab2af23dc45757015f2bcdda93f9dc
Author: Philip Herron <[email protected]>
Date:   Wed Jun 24 16:28:11 2026 +0100

    gccrs: Fix ICE when trying to resolve const expr
    
    We cannot resolve N + 1 a this stage since N has no default and is const
    generic, rustc makes a more precise error diag here but our one is
    completely fine for now.
    
    Fixes Rust-GCC#4302
    
    gcc/rust/ChangeLog:
    
            * backend/rust-compile-resolve-path.cc: use error_mark_node
    
    gcc/testsuite/ChangeLog:
    
            * rust/compile/issue-4302.rs: New test.
    
    Signed-off-by: Philip Herron <[email protected]>

Diff:
---
 gcc/rust/backend/rust-compile-resolve-path.cc |  4 +++-
 gcc/testsuite/rust/compile/issue-4302.rs      | 12 ++++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/gcc/rust/backend/rust-compile-resolve-path.cc b/gcc/rust/backend/rust-compile-resolve-path.cc
index d665df70f07e..d9225718b136 100644
--- a/gcc/rust/backend/rust-compile-resolve-path.cc
+++ b/gcc/rust/backend/rust-compile-resolve-path.cc
@@ -194,7 +194,9 @@ ResolvePathRef::resolve_with_node_id (
       auto d = lookup->destructure ();
       rust_assert (d->get_kind () == TyTy::TypeKind::CONST);
       auto c = d->as_const_type ();
-      rust_assert (c->const_kind () == TyTy::BaseConstType::ConstKind::Value);
+      if (c->const_kind () != TyTy::BaseConstType::ConstKind::Value)
+	return error_mark_node;
+
       auto val = static_cast<TyTy::ConstValueType *> (c);
       return val->get_value ();
     }
diff --git a/gcc/testsuite/rust/compile/issue-4302.rs b/gcc/testsuite/rust/compile/issue-4302.rs
new file mode 100644
index 000000000000..2ba30551b2a9
--- /dev/null
+++ b/gcc/testsuite/rust/compile/issue-4302.rs
@@ -0,0 +1,12 @@
+#![feature(no_core, intrinsics, staged_api, lang_items)]
+#![no_core]
+
+#[lang = "sized"]
+pub trait Sized {}
+
+pub struct Foo<const N: usize>;
+
+pub fn foo<const N: usize>() -> Foo<{ N + 1 }> {
+    // { dg-error "failed to resolve const expression" "" { target *-*-* } .-1 }
+    Foo
+}