[Ada] Scalar_Storage_Order consistency for nested composites

[Arnaud Charlet <charlet at adacore dot com>]

Scalar_Storage_Order must be consistent between any component of a composite
type (array or record) and the composite type itself. We already enforced
this in the case where the enclosing type has a Scalar_Storage_Order
attribute definition, and the component type has none. We now also do so
also in the opposite case when the enclosing type has no Scalar_Storage_Order
clause, and any component does have one.

The following compilation must be rejected with the indicated error messages:

$ gcc -c nat_comp_rev_el.ads
nat_comp_rev_el.ads:26:04: composite type must have explicit scalar storage order
nat_comp_rev_el.ads:27:04: composite type must have explicit scalar storage order
nat_comp_rev_el.ads:29:07: composite type must have explicit scalar storage order
nat_comp_rev_el.ads:34:07: composite type must have explicit scalar storage order

with System; use System;
package Nat_Comp_Rev_El is
   type U32 is mod 2**32;

   type LE_Record is record
      X : U32;
   end record;
   for LE_Record use record
      X at 0 range 0 .. 31;
   end record;
   for LE_Record'Bit_Order use Low_Order_First;
   for LE_Record'Scalar_Storage_Order use Low_Order_First;

   type BE_Record is record
      X : U32;
   end record;
   for BE_Record use record
      X at 0 range 0 .. 31;
   end record;
   for BE_Record'Bit_Order use High_Order_First;
   for BE_Record'Scalar_Storage_Order use High_Order_First;

   --  Reject the below declarations: the component type has an explicit SSO,
   --  so we also require one on the enclosing composite type.

   type Two_LE is array (1 .. 2) of LE_Record;
   type Two_BE is array (1 .. 2) of BE_Record;
   type Rec_LE is record
      Comp : LE_Record;
      X    : Integer;
   end record;

   type Rec_BE is record
      Comp : BE_Record;
      X    : Integer;
   end record;

end Nat_Comp_Rev_El;

Tested on x86_64-pc-linux-gnu, committed on trunk

2013-10-17  Thomas Quinot  <quinot@adacore.com>

	* freeze.adb (Check_Component_Storage_Order): Reject a record or
	array type that does not have an explicit Scalar_Storage_Order
	attribute definition if a component of the record, or the
	elements of the array, have one.
	* gnat_rm.texi (attribute Scalar_Storage_Order): Document the above
	rule.

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