Add raw identifier ui test

tests/ui/raw_ident_namespace.rs

@@ -0,0 +1,53 @@
+use cxx::{type_id, ExternType};
+
+#[repr(transparent)]
+pub struct QuotedRaw(usize);
+
+unsafe impl ExternType for QuotedRaw {
+    type Id = type_id!("org::r#box::implementation::QuotedRaw");
+    type Kind = cxx::kind::Trivial;
+}
+
+#[repr(transparent)]
+pub struct QuotedKeyword(usize);
+
+unsafe impl ExternType for QuotedKeyword {
+    type Id = type_id!("org::box::implementation::QuotedKeyword");
+    type Kind = cxx::kind::Trivial;
+}
+
+#[repr(transparent)]
+pub struct UnquotedRaw(usize);
+
+unsafe impl ExternType for UnquotedRaw {
+    type Id = type_id!(org::r#box::implementation::UnquotedRaw);
+    type Kind = cxx::kind::Trivial;
+}
+
+#[repr(transparent)]
+pub struct UnquotedKeyword(usize);
+
+unsafe impl ExternType for UnquotedKeyword {
+    type Id = type_id!(org::box::implementation::UnquotedKeyword);
+    type Kind = cxx::kind::Trivial;
+}
+
+#[cxx::bridge]
+pub mod ffi {
+    extern "C++" {
+        #[namespace = "org::r#box::implementation"]
+        type QuotedRaw = crate::QuotedRaw;
+
+        #[namespace = "org::box::implementation"]
+        type QuotedKeyword = crate::QuotedKeyword;
+
+        #[namespace = org::r#box::implementation]
+        type UnquotedRaw = crate::UnquotedRaw;
+
+        // Not allowed by rustc (independent of cxx):
+        // #[namespace = org::box::implementation]
+        // type UnquotedKeyword = crate::UnquotedKeyword;
+    }
+}
+
+fn main() {}

tests/ui/raw_ident_namespace.stderr

@@ -0,0 +1,11 @@
+error: raw identifier `r#box` is not allowed in a quoted namespace
+ --> tests/ui/raw_ident_namespace.rs:7:24
+  |
+7 |     type Id = type_id!("org::r#box::implementation::QuotedRaw");
+  |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: raw identifier `r#box` is not allowed in a quoted namespace
+  --> tests/ui/raw_ident_namespace.rs:38:23
+   |
+38 |         #[namespace = "org::r#box::implementation"]
+   |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^