Improve error for shared alias receiver type plus tests

Author: sbrocket

syntax/check.rs

@@ -227,12 +227,20 @@ fn check_api_fn(cx: &mut Check, efn: &ExternFn) {
                 mutability = mutability,
             );
             cx.error(span, msg);
+        } else if cx.types.aliases.contains_key(&receiver.ty)
+            && !cx.types.cxx.contains(&receiver.ty)
+        {
+            // We cannot add class member functions to the type generated by the other bridge, plus
+            // we can't tell whether the alias is for a struct or enum and only the former can have
+            // member functions.
+            cx.error(
+                span,
+                "shared type aliases cannot be used as a receiver type",
+            )
         } else if !cx.types.structs.contains_key(&receiver.ty)
             && !cx.types.cxx.contains(&receiver.ty)
             && !cx.types.rust.contains(&receiver.ty)
         {
-            // TODO: Add ui test for aliases being disallowed in receiver position since we can't
-            // tell if it's a struct or enum, unique error message
             cx.error(span, "unrecognized receiver type");
         }
 

tests/ffi/alias.rs

@@ -30,6 +30,9 @@ pub mod ffi {
         fn alias_c_take_unique_ptr_vector_shared(v: UniquePtr<CxxVector<Shared>>);
         fn alias_c_take_rust_vec_shared(v: Vec<Shared>);
         fn alias_c_take_enum(e: Enum);
+
+        fn get3(self: &C) -> usize;
+        fn set3(self: &mut C, n: usize) -> usize;
     }
 
     extern "Rust" {

tests/ffi/tests.cc

@@ -20,6 +20,8 @@ size_t C::get() const { return this->n; }
 
 size_t C::get2() const { return this->n; }
 
+size_t C::get3() const { return this->n; }
+
 size_t C::set(size_t n) {
   this->n = n;
   return this->n;
@@ -30,6 +32,11 @@ size_t C::set2(size_t n) {
   return this->n;
 }
 
+size_t C::set3(size_t n) {
+  this->n = n;
+  return this->n;
+}
+
 size_t C::set_succeed(size_t n) { return this->set2(n); }
 
 size_t C::get_fail() { throw std::runtime_error("unimplemented"); }

tests/ffi/tests.h

@@ -16,6 +16,8 @@ class C {
   size_t set(size_t n);
   size_t get2() const;
   size_t set2(size_t n);
+  size_t get3() const;
+  size_t set3(size_t n);
   size_t set_succeed(size_t n);
   size_t get_fail();
   const std::vector<uint8_t> &get_v() const;

tests/test.rs

@@ -234,6 +234,16 @@ fn test_c_method_calls() {
     assert!(unique_ptr.get_fail().is_err());
 }
 
+#[test]
+fn test_alias_c_method_calls() {
+    let mut unique_ptr = alias::ffi::alias_c_return_unique_ptr();
+
+    let old_value = unique_ptr.get3();
+    assert_eq!(2020, old_value);
+    assert_eq!(2021, unique_ptr.set3(2021));
+    assert_eq!(2021, unique_ptr.get3());
+}
+
 #[test]
 fn test_enum_representations() {
     assert_eq!(0, ffi::Enum::AVal.repr);

tests/ui/alias_receiver_type.rs

@@ -0,0 +1,27 @@
+#[cxx::bridge]
+mod here {
+    struct Shared {
+        z: usize,
+    }
+
+    extern "C" {
+        type C;
+    }
+}
+
+// Rustfmt mangles the extern type alias.
+// https://github.com/rust-lang/rustfmt/issues/4159
+// ...normally would add #[rustfmt::skip], but that seems to interfere with the error spans.
+#[cxx::bridge]
+mod there {
+    type Shared = crate::here::Shared;
+
+    extern "C" {
+        type C = crate::here::C;
+
+        fn good(self: &C);
+        fn bad(self: &Shared);
+    }
+}
+
+fn main() {}

tests/ui/alias_receiver_type.stderr

@@ -0,0 +1,5 @@
+error: shared type aliases cannot be used as a receiver type
+  --> $DIR/alias_receiver_type.rs:23:22
+   |
+23 |         fn bad(self: &Shared);
+   |                      ^^^^^^^