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.

4 files changed, 19 insertions, 8 deletions

diff --git a/cparser/Checks.ml b/cparser/Checks.ml
index 62d85c1b..a30cde7d 100644
--- a/cparser/Checks.ml
+++ b/cparser/Checks.ml
@@ -18,19 +18,12 @@ open Diagnostics
 open Cutil
 open Env
 
-let attribute_string = function
-  | AConst -> "const"
-  | AVolatile -> "volatile"
-  | ARestrict -> "restrict"
-  | AAlignas n -> "_Alignas"
-  | Attr(name, _) ->  name
-
 let unknown_attrs loc attrs =
   let unknown attr =
     let attr_class = class_of_attribute attr in
     if attr_class = Attr_unknown then
       warning loc Unknown_attribute
-        "unknown attribute '%s' ignored" (attribute_string attr) in
+        "unknown attribute '%s' ignored" (name_of_attribute attr) in
   List.iter unknown attrs
 
 let unknown_attrs_typ env loc ty =
diff --git a/cparser/Cutil.ml b/cparser/Cutil.ml
index 25329694..cf67015a 100644
--- a/cparser/Cutil.ml
+++ b/cparser/Cutil.ml
@@ -119,6 +119,15 @@ let class_of_attribute = function
       try Hashtbl.find attr_class (normalize_attrname name)
       with Not_found -> Attr_unknown
 
+(* Name for printing an attribute *)
+
+let name_of_attribute = function
+  | AConst -> "const"
+  | AVolatile -> "volatile"
+  | ARestrict -> "restrict"
+  | AAlignas n -> "_Alignas"
+  | Attr(name, _) ->  name
+
 (* Is an attribute a ISO C standard attribute? *)
 
 let attr_is_standard = function
diff --git a/cparser/Cutil.mli b/cparser/Cutil.mli
index 400a6319..5a1e9af3 100644
--- a/cparser/Cutil.mli
+++ b/cparser/Cutil.mli
@@ -81,6 +81,8 @@ val class_of_attribute: attribute -> attribute_class
      have class [Attr_type].  Custom attributes have the class that
      was given to them using [declare_attribute], or [Attr_unknown]
      if not declared. *)
+val name_of_attribute: attribute -> string
+  (* Name for printing an attribute *)
 val attr_inherited_by_members: attribute -> bool
   (* Is an attribute of a composite inherited by members of the composite? *)
 
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