Reject object-related and struct-related attributes on typedefs

This commit adds a check to reject type definitions such as
```
typedef __attribute((section "foo")) int fooint;
```
GCC and Clang also reject this as an error.

Without the check, the behavior is somewhat surprising:
```
fooint x;    // placed in section "foo"
fooint * x;  // placed in default section, attribute "foo" is ignored
```

Note that the following must be accepted:
```
typedef struct { ... } __attribute((packed)) t;
```
The "packed" attribute is correctly attached to the struct type and should not be checked.  This is achieved by using `attribute_of_type_no_expand` to get the attributes of the typedef-ed type, excluding the attributes carried by a struct/union or another typedef.

1 files changed, 7 insertions, 0 deletions

diff --git a/cparser/Elab.ml b/cparser/Elab.ml
index 46bc63a9..d7124663 100644
--- a/cparser/Elab.ml
+++ b/cparser/Elab.ml
@@ -2366,6 +2366,13 @@ let enter_typedefs loc env sto dl =
       error loc "initializer in typedef";
     if has_std_alignas env ty then
       error loc "alignment specified for typedef '%s'" s;
+    List.iter
+      (fun a -> match class_of_attribute a with
+                | Attr_object | Attr_struct ->
+                    error loc "attribute '%s' not allowed in 'typedef'"
+                              (name_of_attribute a)
+                | _ -> ())
+      (attributes_of_type_no_expand ty);
     match previous_def Env.lookup_typedef env s with
     | Some (s',ty') when Env.in_current_scope env s' ->
         if equal_types env ty ty' then begin