Support type aliases across bridges using different C++ namespaces

gen/src/write.rs

@@ -936,7 +936,10 @@ fn write_type(out: &mut OutFile, ty: &Type) {
 
 fn write_alias(out: &mut OutFile, alias: &TypeAlias) {
     if let Some(namespace) = &alias.namespace {
-        let path = namespace.path_for_type(&alias.ident);
+        // Review TODO: Is this unwrap fine? i.e. is it ok to assume that, if
+        // the TypePath parsed, that it has at least one segment?
+        let remote_type = &alias.ty.path.segments.last().unwrap().ident;
+        let path = namespace.path_for_type(remote_type);
         writeln!(out, "using {} = {};", alias.ident, path)
     }
 }

macro/src/expand.rs

@@ -668,8 +668,11 @@ fn expand_type_alias(alias: &TypeAlias) -> TokenStream {
 
 fn expand_type_alias_verify(namespace: &Namespace, alias: &TypeAlias) -> TokenStream {
     let namespace = alias.namespace.as_ref().unwrap_or(namespace);
+    // Review TODO: Is this unwrap fine? i.e. is it ok to assume that, if the
+    // TypePath parsed, that it has at least one segment?
+    let remote_type = &alias.ty.path.segments.last().unwrap().ident;
+    let type_id = type_id(namespace, remote_type);
     let ident = &alias.ident;
-    let type_id = type_id(namespace, ident);
     let begin_span = alias.type_token.span;
     let end_span = alias.semi_token.span;
     let begin = quote_spanned!(begin_span=> ::cxx::private::verify_extern_type::<);

tests/ffi/alias.rs

@@ -11,7 +11,10 @@ pub mod ffi {
         #[namespace = "tests"]
         type C = crate::ffi::C;
 
+        #[namespace = "tests"]
+        type SameC = crate::ffi::C;
+
         fn c_return_unique_ptr() -> UniquePtr<C>;
-        fn c_take_unique_ptr(c: UniquePtr<C>);
+        fn c_take_unique_ptr(c: UniquePtr<SameC>);
     }
 }

tests/ui/wrong_type_id.rs

@@ -1,14 +1,17 @@
-#[cxx::bridge(namespace = folly)]
+#[cxx::bridge(namespace = correct)]
 mod here {
     extern "C" {
         type StringPiece;
     }
 }
 
+// Rustfmt mangles the extern type alias.
+// https://github.com/rust-lang/rustfmt/issues/4159
+#[rustfmt::skip]
 #[cxx::bridge(namespace = folly)]
 mod there {
     extern "C" {
-        type ByteRange = crate::here::StringPiece;
+        type OtherName = crate::here::StringPiece;
     }
 }
 

tests/ui/wrong_type_id.stderr

@@ -1,13 +1,13 @@
-error[E0271]: type mismatch resolving `<StringPiece as ExternType>::Id == (f, o, l, l, y, (), B, y, t, e, R, a, n, g, e)`
-   --> $DIR/wrong_type_id.rs:11:9
+error[E0271]: type mismatch resolving `<StringPiece as ExternType>::Id == (f, o, l, l, y, (), S, t, r, i, n, g, P, i, e, c, e)`
+   --> $DIR/wrong_type_id.rs:11:1
     |
-11  |         type ByteRange = crate::here::StringPiece;
-    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected a tuple with 15 elements, found one with 17 elements
+11  | #[cxx::bridge(namespace = folly)]
+    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected a tuple with 17 elements, found one with 19 elements
     |
    ::: $WORKSPACE/src/extern_type.rs
     |
     | pub fn verify_extern_type<T: ExternType<Id = Id>, Id>() {}
     |                                         ------- required by this bound in `verify_extern_type`
     |
-    = note: expected tuple `(f, o, l, l, y, (), B, y, t, e, R, a, n, g, e)`
-               found tuple `(f, o, l, l, y, (), S, t, r, i, n, g, P, i, e, c, e)`
+    = note: expected tuple `(f, o, l, l, y, (), S, t, r, i, n, g, P, i, e, c, e)`
+               found tuple `(c, o, r, r, e, c, t, (), S, t, r, i, n, g, P, i, e, c, e)`