Revised attachment of name attributes to structs, unions, enums

Consider:
```
struct s { ... } __attribute((aligned(N)));

struct t { ... }
 __attribute((aligned(N))) struct t x;
```
In the first case, the aligned attribute should be attached to struct s, so that further references to struct s are aligned.

In the second case, the aligned attribute should be attached to the variable x, because if we attach it to struct t, it will be ignored and cause a warning.

This commit changes the attachment rule so that it treats both cases right.

Extend regression test for "aligned" attribute accordingly, by testing
aligned attribute applied to a name of struct type.

3 files changed, 29 insertions, 6 deletions

diff --git a/cparser/Elab.ml b/cparser/Elab.ml
index d7124663..7a0b05de 100644
--- a/cparser/Elab.ml
+++ b/cparser/Elab.ml
@@ -661,12 +661,24 @@ let rec elab_specifier ?(only = false) loc env specifier =
      The returned name-or-struct-related attributes are applied to the
      struct/union/enum being defined.
      The leftover attributes (e.g. object attributes) will be applied
-     to the variable being defined. *)
-  let get_definition_attrs () =
+     to the variable being defined.
+     If [optmembers] is [None], name-related attributes are not returned
+     but left in !attr.  This corresponds to two use cases:
+     - A use of an already-defined struct/union/enum.  In this case
+       the name-related attributes should go to the name being declared.
+       Sending them to the struct/union/enum would cause them to be ignored,
+       with a warning.  The struct-related attributes go to the 
+       struct/union/enum, are ignored, and cause a warning.
+     - An incomplete declaration of a struct/union.  In this case
+       the name- and struct-related attributes are just ignored,
+       like GCC does.
+  *)
+  let get_definition_attrs optmembers =
     let (ta, nta) =
       List.partition
         (fun a -> match class_of_attribute a with
-                  | Attr_struct | Attr_name -> true
+                  | Attr_struct -> true
+                  | Attr_name -> optmembers <> None
                   | _ -> false)
         !attr in
     attr := nta;
@@ -727,7 +739,8 @@ let rec elab_specifier ?(only = false) loc env specifier =
 
     | [Cabs.Tstruct_union(STRUCT, id, optmembers, a)] ->
         let a' =
-          add_attributes (get_definition_attrs()) (elab_attributes env a) in
+          add_attributes (get_definition_attrs optmembers)
+                         (elab_attributes env a) in
         let (id', env') =
           elab_struct_or_union only Struct loc id optmembers a' env in
         let ty =  TStruct(id', !attr) in
@@ -736,7 +749,8 @@ let rec elab_specifier ?(only = false) loc env specifier =
 
     | [Cabs.Tstruct_union(UNION, id, optmembers, a)] ->
         let a' =
-          add_attributes (get_definition_attrs()) (elab_attributes env a) in
+          add_attributes (get_definition_attrs optmembers)
+                         (elab_attributes env a) in
         let (id', env') =
           elab_struct_or_union only Union loc id optmembers a' env in
         let ty =  TUnion(id', !attr) in
@@ -745,7 +759,8 @@ let rec elab_specifier ?(only = false) loc env specifier =
 
     | [Cabs.Tenum(id, optmembers, a)] ->
         let a' =
-          add_attributes (get_definition_attrs()) (elab_attributes env a) in
+          add_attributes (get_definition_attrs optmembers)
+                         (elab_attributes env a) in
         let (id', env') =
           elab_enum only loc id optmembers a' env in
         let ty = TEnum (id', !attr) in
diff --git a/test/regression/Results/aligned b/test/regression/Results/aligned
index 7a4f7c9f..c42a5c40 100644
--- a/test/regression/Results/aligned
+++ b/test/regression/Results/aligned
@@ -9,3 +9,4 @@ i: size 16, offset mod 16 = 0
 j: size 16, offset mod 16 = 0
 T2: size 112, alignment 16
 T4: size is that of a pointer, alignment is that of a pointer
+t2: size 9, alignment 1
diff --git a/test/regression/aligned.c b/test/regression/aligned.c
index 3b5a9374..bd16d513 100644
--- a/test/regression/aligned.c
+++ b/test/regression/aligned.c
@@ -3,6 +3,7 @@
 #include <stdio.h>
 
 #define ALIGNED __attribute((aligned(16)))
+#define ALIGNED1 __attribute((aligned(1)))
 
 typedef ALIGNED char c16;
 
@@ -72,6 +73,10 @@ typedef T2 T3[];
 typedef struct { T3 *area; } T4;
 /* Expected: size of a pointer, alignment of a pointer */
 
+struct t1 { double d; };
+struct t2 { char c; ALIGNED1 struct t1 d; };
+/* Expected: size = 1 + 8, alignment 1 */
+
 void check(const char * msg, void * addr, size_t sz)
 {
   printf("%s: size %zu, offset mod 16 = %lu\n",
@@ -104,5 +109,7 @@ int main()
          sizeof(T4) == sizeof(void *) ? "is" : "IS NOT",
          _Alignof(T4) == _Alignof(void *) ? "is" : "IS NOT");
 
+  printf("t2: size %zu, alignment %zu\n",
+         sizeof(struct t2), _Alignof(struct t2));
   return 0;
 }