ada: Switch from E_Void to Is_Not_Self_Hidden

We had previously used Ekind = E_Void to indicate that a declaration is
self-hidden. We now use the Is_Not_Self_Hidden flag instead. This allows
us to avoid many "vanishing fields", which are (possibly-latent) bugs,
and we now enable the assertions in Atree that detect such bugs.

gcc/ada/

	* atree.adb (Check_Vanishing_Fields): Fix bug in the "blah type
	only" cases. Remove the special cases for E_Void. Misc cleanup.
	(Mutate_Nkind): Disallow mutating to the same kind.
	(Mutate_Ekind): Disallow mutating to E_Void.
	(From E_Void is still OK -- entities start out as E_Void by
	default.) Fix bug in statistics gathering -- was setting the wrong
	count. Enable Check_Vanishing_Fields for entities.
	* sem_ch8.adb (Is_Self_Hidden): New function.
	(Find_Direct_Name): Call Is_Self_Hidden to use the new
	Is_Not_Self_Hidden flag to determine whether a declaration is
	hidden from all visibility by itself. This replaces the old method
	of checking E_Void.
	(Find_Expanded_Name): Likewise.
	(Find_Selected_Component): Likewise.
	* sem_util.adb (Enter_Name): Remove setting of Ekind to E_Void.
	* sem_ch3.adb: Set the Is_Not_Self_Hidden flag in appropriate
	places. Comment fixes.
	(Inherit_Component): Remove setting of Ekind to E_Void.
	* sem_ch9.adb
	(Analyze_Protected_Type_Declaration): Update comment. Skip Itypes,
	which should not be turned into components.
	* atree.ads (Mutate_Nkind): Document error case.
	(Mutate_Ekind): Remove comments apologizing for E_Void mutations.
	Document error cases.

1 files changed, 24 insertions, 26 deletions

diff --git a/gcc/ada/sem_ch3.adb b/gcc/ada/sem_ch3.adb
index db2bbb5..1ed590ba 100644
--- a/gcc/ada/sem_ch3.adb
+++ b/gcc/ada/sem_ch3.adb
@@ -7589,6 +7589,7 @@ package body Sem_Ch3 is
             end if;
 
             Mutate_Ekind             (New_Lit, E_Enumeration_Literal);
+            Set_Is_Not_Self_Hidden   (New_Lit);
             Set_Enumeration_Pos      (New_Lit, Enumeration_Pos (Literal));
             Set_Enumeration_Rep      (New_Lit, Enumeration_Rep (Literal));
             Set_Enumeration_Rep_Expr (New_Lit, Empty);
@@ -8123,6 +8124,7 @@ package body Sem_Ch3 is
             Build_Derived_Type
               (N, Full_Parent, Full_Der,
                Is_Completion => False, Derive_Subps => False);
+            Set_Is_Not_Self_Hidden (Full_Der);
          end if;
 
          Set_Has_Private_Declaration (Full_Der);
@@ -9917,8 +9919,8 @@ package body Sem_Ch3 is
 
       --  There is no completion for record extensions declared in the
       --  parameter part of a generic, so we need to complete processing for
-      --  these generic record extensions here. The Record_Type_Definition call
-      --  will change the Ekind of the components from E_Void to E_Component.
+      --  these generic record extensions here. Record_Type_Definition will
+      --  set the Is_Not_Self_Hidden flag.
 
       elsif Private_Extension and then Is_Generic_Type (Derived_Type) then
          Record_Type_Definition (Empty, Derived_Type);
@@ -11959,6 +11961,8 @@ package body Sem_Ch3 is
          return;
       end if;
 
+      Set_Is_Not_Self_Hidden (Typ);
+
       Comp := First (Component_Items (Comp_List));
       while Present (Comp) loop
          if Nkind (Comp) = N_Component_Declaration then
@@ -12930,13 +12934,14 @@ package body Sem_Ch3 is
 
       --  Set common attributes for all subtypes: kind, convention, etc.
 
-      Mutate_Ekind         (Full, Subtype_Kind (Ekind (Full_Base)));
-      Set_Convention       (Full, Convention (Full_Base));
+      Mutate_Ekind (Full, Subtype_Kind (Ekind (Full_Base)));
+      Set_Is_Not_Self_Hidden (Full);
+      Set_Convention (Full, Convention (Full_Base));
       Set_Is_First_Subtype (Full, False);
-      Set_Scope            (Full, Scope (Priv));
-      Set_Size_Info        (Full, Full_Base);
-      Copy_RM_Size         (To => Full, From => Full_Base);
-      Set_Is_Itype         (Full);
+      Set_Scope (Full, Scope (Priv));
+      Set_Size_Info (Full, Full_Base);
+      Copy_RM_Size (To => Full, From => Full_Base);
+      Set_Is_Itype (Full);
 
       --  A subtype of a private-type-without-discriminants, whose full-view
       --  has discriminants with default expressions, is not constrained.
@@ -15094,6 +15099,7 @@ package body Sem_Ch3 is
       --  in the private part is the full declaration.
 
       Exchange_Entities (Priv, Full);
+      Set_Is_Not_Self_Hidden (Priv);
       Append_Entity (Full, Scope (Full));
    end Copy_And_Swap;
 
@@ -16046,6 +16052,7 @@ package body Sem_Ch3 is
    begin
       New_Subp := New_Entity (Nkind (Parent_Subp), Sloc (Derived_Type));
       Mutate_Ekind (New_Subp, Ekind (Parent_Subp));
+      Set_Is_Not_Self_Hidden (New_Subp);
 
       --  Check whether the inherited subprogram is a private operation that
       --  should be inherited but not yet made visible. Such subprograms can
@@ -17662,6 +17669,8 @@ package body Sem_Ch3 is
 
       --  Avoid deriving parent primitives of underlying record views
 
+      Set_Is_Not_Self_Hidden (T);
+
       Build_Derived_Type (N, Parent_Type, T, Is_Completion,
         Derive_Subps => not Is_Underlying_Record_View (T));
 
@@ -17750,6 +17759,7 @@ package body Sem_Ch3 is
       while Present (L) loop
          if Ekind (L) /= E_Enumeration_Literal then
             Mutate_Ekind (L, E_Enumeration_Literal);
+            Set_Is_Not_Self_Hidden (L);
             Set_Enumeration_Pos (L, Ev);
             Set_Enumeration_Rep (L, Ev);
             Set_Is_Known_Valid  (L, True);
@@ -19197,22 +19207,6 @@ package body Sem_Ch3 is
             end if;
          end if;
 
-         --  In derived tagged types it is illegal to reference a non
-         --  discriminant component in the parent type. To catch this, mark
-         --  these components with an Ekind of E_Void. This will be reset in
-         --  Record_Type_Definition after processing the record extension of
-         --  the derived type.
-
-         --  If the declaration is a private extension, there is no further
-         --  record extension to process, and the components retain their
-         --  current kind, because they are visible at this point.
-
-         if Is_Tagged and then Ekind (New_C) = E_Component
-           and then Nkind (N) /= N_Private_Extension_Declaration
-         then
-            Mutate_Ekind (New_C, E_Void);
-         end if;
-
          if Plain_Discrim then
             Set_Corresponding_Discriminant (New_C, Old_C);
             Build_Discriminal (New_C);
@@ -20222,6 +20216,7 @@ package body Sem_Ch3 is
       Op := Make_Defining_Operator_Symbol (Loc, Name_Op_Concat);
 
       Mutate_Ekind                (Op, E_Operator);
+      Set_Is_Not_Self_Hidden      (Op);
       Set_Scope                   (Op, Current_Scope);
       Set_Etype                   (Op, Typ);
       Set_Homonym                 (Op, Get_Name_Entity_Id (Name_Op_Concat));
@@ -20940,6 +20935,7 @@ package body Sem_Ch3 is
          end if;
 
          Mutate_Ekind (Id, E_Discriminant);
+         Set_Is_Not_Self_Hidden (Id);
          Reinit_Component_Location (Id);
          Reinit_Esize (Id);
          Set_Discriminant_Number (Id, Discr_Number);
@@ -22762,6 +22758,8 @@ package body Sem_Ch3 is
          T := Prev_T;
       end if;
 
+      Set_Is_Not_Self_Hidden (T);
+
       Final_Storage_Only := not Is_Controlled (T);
 
       --  Ada 2005: Check whether an explicit "limited" is present in a derived
@@ -22803,6 +22801,7 @@ package body Sem_Ch3 is
          then
             Mutate_Ekind (Component, E_Component);
             Reinit_Component_Location (Component);
+            Set_Is_Not_Self_Hidden (Component);
          end if;
 
          Propagate_Concurrent_Flags (T, Etype (Component));
@@ -23022,9 +23021,8 @@ package body Sem_Ch3 is
       --  Reset the kind of the subtype during analysis of the range, to
       --  catch possible premature use in the bounds themselves.
 
-      Mutate_Ekind (Def_Id, E_Void);
       Process_Range_Expr_In_Decl (R, Subt, Subtyp => Def_Id);
-      Mutate_Ekind (Def_Id, Kind);
+      pragma Assert (Ekind (Def_Id) = Kind);
    end Set_Scalar_Range_For_Subtype;
 
    --------------------------------------------------------