[Ada] Implement AI12-0275 (Make subtype_mark optional in object renamings)

2020-06-04  Gary Dismukes  <dismukes@adacore.com>

gcc/ada/

	* par-ch3.adb (P_Identifier_Declarations): Add parsing of object
	renamings that have neither a subtype_mark nor an
	access_definition. Issue an error if the version is earlier than
	Ada_2020, and suggest using -gnatX.
	* sem_ch8.adb (Analyze_Object_Renaming): Handle
	object_renaming_declarations that don't have an explicit
	subtype. Errors are issued when the name is inappropriate or
	ambiguous, and otherwise the Etype of the renaming entity is set
	from the Etype of the renamed object.
	* sem_util.adb (Has_Null_Exclusion): Allow for the case of no
	subtype given in an N_Object_Renaming_Declaration.
	* sprint.adb (Sprint_Node_Actual): Handle printing of
	N_Object_Renaming_Declarations that are specified without an
	explicit subtype.

4 files changed, 145 insertions, 7 deletions

diff --git a/gcc/ada/par-ch3.adb b/gcc/ada/par-ch3.adb
index a54577e..9065f4b 100644
--- a/gcc/ada/par-ch3.adb
+++ b/gcc/ada/par-ch3.adb
@@ -1480,6 +1480,32 @@ package body Ch3 is
          Done := False;
          return;
 
+      --  AI12-0275: Object renaming declaration without subtype_mark or
+      --  access_definition
+
+      elsif Token = Tok_Renames then
+         if Ada_Version < Ada_2020 then
+            Error_Msg_SC
+              ("object renaming without subtype is an Ada 202x feature");
+            Error_Msg_SC ("\compile with -gnatX");
+         end if;
+
+         Scan; -- past renames
+
+         Decl_Node :=
+           New_Node (N_Object_Renaming_Declaration, Ident_Sloc);
+         Set_Name (Decl_Node, P_Name);
+         Set_Defining_Identifier (Decl_Node, Idents (1));
+
+         P_Aspect_Specifications (Decl_Node, Semicolon => False);
+
+         T_Semicolon;
+
+         Append (Decl_Node, Decls);
+         Done := False;
+
+         return;
+
       --  Otherwise we have an error situation
 
       else
diff --git a/gcc/ada/sem_ch8.adb b/gcc/ada/sem_ch8.adb
index 76f696b..4a730fc 100644
--- a/gcc/ada/sem_ch8.adb
+++ b/gcc/ada/sem_ch8.adb
@@ -906,10 +906,108 @@ package body Sem_Ch8 is
             Find_Type (Subtype_Mark (N));
          end if;
 
-      elsif Present (Subtype_Mark (N)) then
-         Find_Type (Subtype_Mark (N));
-         T := Entity (Subtype_Mark (N));
-         Analyze (Nam);
+      elsif Present (Subtype_Mark (N))
+        or else not Present (Access_Definition (N))
+      then
+         if Present (Subtype_Mark (N)) then
+            Find_Type (Subtype_Mark (N));
+            T := Entity (Subtype_Mark (N));
+            Analyze (Nam);
+
+         --  AI12-0275: Case of object renaming without a subtype_mark
+
+         else
+            Analyze (Nam);
+
+            --  Normal case of no overloading in object name
+
+            if not Is_Overloaded (Nam) then
+
+               --  Catch error cases (such as attempting to rename a procedure
+               --  or package) using the shorthand form.
+
+               if No (Etype (Nam))
+                 or else Etype (Nam) = Standard_Void_Type
+               then
+                  Error_Msg_N ("object name expected in renaming", Nam);
+
+                  Set_Ekind (Id, E_Variable);
+                  Set_Etype (Id, Any_Type);
+
+                  return;
+
+               else
+                  T := Etype (Nam);
+               end if;
+
+            --  Case of overloaded name, which will be illegal if there's more
+            --  than one acceptable interpretation (such as overloaded function
+            --  calls).
+
+            else
+               declare
+                  I    : Interp_Index;
+                  I1   : Interp_Index;
+                  It   : Interp;
+                  It1  : Interp;
+                  Nam1 : Entity_Id;
+
+               begin
+                  --  More than one candidate interpretation is available
+
+                  --  Remove procedure calls, which syntactically cannot appear
+                  --  in this context, but which cannot be removed by type
+                  --  checking, because the context does not impose a type.
+
+                  Get_First_Interp (Nam, I, It);
+                  while Present (It.Typ) loop
+                     if It.Typ = Standard_Void_Type then
+                        Remove_Interp (I);
+                     end if;
+
+                     Get_Next_Interp (I, It);
+                  end loop;
+
+                  Get_First_Interp (Nam, I, It);
+                  I1  := I;
+                  It1 := It;
+
+                  --  If there's no type present, we have an error case (such
+                  --  as overloaded procedures named in the object renaming).
+
+                  if No (It.Typ) then
+                     Error_Msg_N ("object name expected in renaming", Nam);
+
+                     Set_Ekind (Id, E_Variable);
+                     Set_Etype (Id, Any_Type);
+
+                     return;
+                  end if;
+
+                  Get_Next_Interp (I, It);
+
+                  if Present (It.Typ) then
+                     Nam1  := It1.Nam;
+                     It1 := Disambiguate (Nam, I1, I, Any_Type);
+
+                     if It1 = No_Interp then
+                        Error_Msg_N ("ambiguous name in object renaming", Nam);
+
+                        Error_Msg_Sloc := Sloc (It.Nam);
+                        Error_Msg_N ("\\possible interpretation#!", Nam);
+
+                        Error_Msg_Sloc := Sloc (Nam1);
+                        Error_Msg_N ("\\possible interpretation#!", Nam);
+
+                        return;
+                     end if;
+                  end if;
+
+                  Set_Etype (Nam, It1.Typ);
+                  T := It1.Typ;
+               end;
+            end if;
+         end if;
 
          --  The object renaming declaration may become Ghost if it renames a
          --  Ghost entity.
diff --git a/gcc/ada/sem_util.adb b/gcc/ada/sem_util.adb
index dff9f81..49594e4 100644
--- a/gcc/ada/sem_util.adb
+++ b/gcc/ada/sem_util.adb
@@ -11726,7 +11726,6 @@ package body Sem_Util is
 
          when N_Component_Definition
             | N_Formal_Object_Declaration
-            | N_Object_Renaming_Declaration
          =>
             if Present (Subtype_Mark (N)) then
                return Null_Exclusion_Present (N);
@@ -11734,6 +11733,15 @@ package body Sem_Util is
                return Null_Exclusion_Present (Access_Definition (N));
             end if;
 
+         when N_Object_Renaming_Declaration =>
+            if Present (Subtype_Mark (N)) then
+               return Null_Exclusion_Present (N);
+            elsif Present (Access_Definition (N)) then
+               return Null_Exclusion_Present (Access_Definition (N));
+            else
+               return False;  -- Case of no subtype in renaming (AI12-0275)
+            end if;
+
          when N_Discriminant_Specification =>
             if Nkind (Discriminant_Type (N)) = N_Access_Definition then
                return Null_Exclusion_Present (Discriminant_Type (N));
diff --git a/gcc/ada/sprint.adb b/gcc/ada/sprint.adb
index 51f0bf4..f177981 100644
--- a/gcc/ada/sprint.adb
+++ b/gcc/ada/sprint.adb
@@ -2441,14 +2441,15 @@ package body Sprint is
             Write_Indent;
             Set_Debug_Sloc;
             Sprint_Node (Defining_Identifier (Node));
-            Write_Str (" : ");
 
             --  Ada 2005 (AI-230): Access renamings
 
             if Present (Access_Definition (Node)) then
+               Write_Str (" : ");
                Sprint_Node (Access_Definition (Node));
 
             elsif Present (Subtype_Mark (Node)) then
+               Write_Str (" : ");
 
                --  Ada 2005 (AI-423): Object renaming with a null exclusion
 
@@ -2458,8 +2459,13 @@ package body Sprint is
 
                Sprint_Node (Subtype_Mark (Node));
 
+            --  AI12-0275: Object_Renaming_Declaration without explicit subtype
+
+            elsif Ada_Version >= Ada_2020 then
+               null;
+
             else
-               Write_Str (" ??? ");
+               Write_Str (" :  ??? ");
             end if;
 
             Write_Str_With_Col_Check (" renames ");