Remove dependency of ui test on whether rust-src is installed

macro/src/expand.rs

@@ -31,11 +31,7 @@ fn expand(namespace: &Namespace, ffi: ItemMod, apis: &[Api], types: &Types) -> T
     for api in apis {
         if let Api::RustType(ety) = api {
             expanded.extend(expand_rust_type(ety));
-            let ident = &ety.ident;
-            let span = ident.span();
-            hidden.extend(quote_spanned! {span=>
-                let _ = ::std::ptr::read::<#ident>;
-            });
+            hidden.extend(expand_rust_type_assert_sized(ety));
         }
     }
 
@@ -426,6 +422,28 @@ fn expand_rust_type(ety: &ExternType) -> TokenStream {
     }
 }
 
+fn expand_rust_type_assert_sized(ety: &ExternType) -> TokenStream {
+    // Rustc will render as follows if not sized:
+    //
+    //     type TheirType;
+    //     -----^^^^^^^^^-
+    //     |    |
+    //     |    doesn't have a size known at compile-time
+    //     required by this bound in `ffi::_::__AssertSized`
+
+    let ident = &ety.ident;
+    let begin_span = Token![::](ety.type_token.span);
+    let sized = quote_spanned! {ety.semi_token.span=>
+        #begin_span std::marker::Sized
+    };
+    quote_spanned! {ident.span()=>
+        let _ = {
+            fn __AssertSized<T: ?#sized + #sized>() {}
+            __AssertSized::<#ident>
+        };
+    }
+}
+
 fn expand_rust_function_shim(namespace: &Namespace, efn: &ExternFn, types: &Types) -> TokenStream {
     let ident = &efn.ident;
     let link_name = mangle::extern_fn(namespace, efn);

syntax/mod.rs

@@ -46,6 +46,7 @@ pub struct ExternType {
     pub doc: Doc,
     pub type_token: Token![type],
     pub ident: Ident,
+    pub semi_token: Token![;],
 }
 
 pub struct Struct {

syntax/parse.rs

@@ -242,6 +242,7 @@ fn parse_extern_type(cx: &mut Errors, foreign_type: &ForeignItemType, lang: Lang
     let doc = attrs::parse_doc(cx, &foreign_type.attrs);
     let type_token = foreign_type.type_token;
     let ident = foreign_type.ident.clone();
+    let semi_token = foreign_type.semi_token;
     let api_type = match lang {
         Lang::Cxx => Api::CxxType,
         Lang::Rust => Api::RustType,
@@ -250,6 +251,7 @@ fn parse_extern_type(cx: &mut Errors, foreign_type: &ForeignItemType, lang: Lang
         doc,
         type_token,
         ident,
+        semi_token,
     }))
 }
 

tests/ui/opaque_not_sized.stderr

@@ -1,13 +1,11 @@
 error[E0277]: the size for values of type `str` cannot be known at compilation time
-   --> $DIR/opaque_not_sized.rs:4:14
-    |
-4   |         type TypeR;
-    |              ^^^^^ doesn't have a size known at compile-time
-    |
-   ::: $RUST/core/src/ptr/mod.rs
-    |
-    | pub unsafe fn read<T>(src: *const T) -> T {
-    |                    - required by this bound in `std::ptr::read`
-    |
-    = help: within `TypeR`, the trait `std::marker::Sized` is not implemented for `str`
-    = note: required because it appears within the type `TypeR`
+ --> $DIR/opaque_not_sized.rs:4:14
+  |
+4 |         type TypeR;
+  |         -----^^^^^-
+  |         |    |
+  |         |    doesn't have a size known at compile-time
+  |         required by this bound in `ffi::_::__AssertSized`
+  |
+  = help: within `TypeR`, the trait `std::marker::Sized` is not implemented for `str`
+  = note: required because it appears within the type `TypeR`