Improve support and diagnostic for type qualified arrays (#118)

* Add diagnostic for type qualified arrays that occur in the wrong place

Arrays with type qualifiers (e.g. int t[const 5]) are only allowed as
function  parameters and for them
only the outermost array type derivation.
Bug 23400

* Keep attributes from array for argument conversion

Type qualifiers of arrays in function parameters are just syntactic sugar
to allow adding them to the resulting pointer type.  Hence, when a
qualified array type such as `int t[const 5]` decays into a pointer type
during argument conversion, the pointer type should be qualified, e.g. `int * const t`.

3 files changed, 18 insertions, 1 deletions

diff --git a/cparser/Cutil.ml b/cparser/Cutil.ml
index dcafbea4..e25a1d84 100644
--- a/cparser/Cutil.ml
+++ b/cparser/Cutil.ml
@@ -824,6 +824,15 @@ let float_rank = function
   | FDouble -> 2
   | FLongDouble -> 3
 
+(* Test for qualified array types *)
+
+let rec is_qualified_array = function
+  | TArray (ty, _, attr) ->
+    List.exists attr_is_standard attr || is_qualified_array ty
+  | TPtr (ty, _) -> is_qualified_array ty
+  | TFun(ty_ret, _, _, _) -> is_qualified_array ty_ret
+  | _ -> false
+
 (* Array and function types "decay" to pointer types in many cases *)
 
 let pointer_decay env t =
@@ -901,7 +910,7 @@ let argument_conversion env t =
   (* Arrays and functions degrade automatically to pointers *)
   (* Other types are not changed *)
   match unroll env t with
-  | TArray(ty, _, _) -> TPtr(ty, [])
+  | TArray(ty, _, attr) -> TPtr(ty, attr)
   | TFun _ as ty -> TPtr(ty, [])
   | _ -> t (* preserve typedefs *)
 
diff --git a/cparser/Cutil.mli b/cparser/Cutil.mli
index 9b09a413..43cbe9bd 100644
--- a/cparser/Cutil.mli
+++ b/cparser/Cutil.mli
@@ -175,6 +175,8 @@ val integer_rank : ikind -> int
   (* Order integer kinds from smaller to bigger *)
 val float_rank : fkind -> int
   (* Order float kinds from smaller to bigger *)
+val is_qualified_array : typ -> bool
+  (* Does the type contain a qualified array type (e.g. int[const 5])? *)
 
 (* Usual conversions over types *)
 
diff --git a/cparser/Elab.ml b/cparser/Elab.ml
index cc7648e0..da5a1d37 100644
--- a/cparser/Elab.ml
+++ b/cparser/Elab.ml
@@ -835,6 +835,8 @@ and elab_parameter env (PARAM (spec, id, decl, attr, loc)) =
     error loc "redefinition of parameter '%s'" id;
   (* replace array and function types by pointer types *)
   let ty1 = argument_conversion env1 ty in
+  if is_qualified_array ty1 then
+    error loc "type qualifier used in non-outermost array type derivation";
   let (id', env2) = Env.enter_ident env1 id sto ty1 in
   ( (id', ty1) , env2)
 
@@ -953,6 +955,8 @@ and elab_field_group env (Field_group (spec, fieldlist, loc)) =
                 error loc "bit-field '%a' width not an integer constant" pp_field id;
                 None,env
           end in
+    if is_qualified_array ty then
+      error loc "type qualifier used in array declarator outside of function prototype";
     let anon_composite = is_anonymous_composite ty in
     if id = "" && not anon_composite && optbitsize = None  then
       warning loc Missing_declarations "declaration does not declare anything";
@@ -2334,6 +2338,8 @@ let enter_decdefs local nonstatic_inline loc env sto dl =
                     (name_of_storage_class sto)
       | _ -> ()
     end;
+    if is_qualified_array ty then
+      error loc "type qualifier used in array declarator outside of function prototype";
     (* Local variable declarations with default storage are treated as 'auto'.
        Local function declarations with default storage remain with
        default storage. *)