[gcc r13-202] [Ada] Suggest use of First_Valid/Last_Valid on type with static predicate

[Pierre-Marie de Rodat <pmderodat@gcc.gnu.org>]

https://gcc.gnu.org/g:655ca5aaa970bb5e6727a72be6c3ba9d9f9d5f09

commit r13-202-g655ca5aaa970bb5e6727a72be6c3ba9d9f9d5f09
Author: Yannick Moy <moy@adacore.com>
Date:   Wed Jan 19 11:19:50 2022 +0100

    [Ada] Suggest use of First_Valid/Last_Valid on type with static predicate
    
    Attributes First_Valid/Last_Valid can be used on types with static
    predicate, instead of First/Last/Range. Include that suggestion in
    the corresponding error message.
    
    gcc/ada/
    
            * sem_util.adb (Bad_Predicated_Subtype_Use): Add continuation
            message.

Diff:
---
 gcc/ada/sem_util.adb | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/gcc/ada/sem_util.adb b/gcc/ada/sem_util.adb
index 1fc2c617afa..d76b5d93511 100644
--- a/gcc/ada/sem_util.adb
+++ b/gcc/ada/sem_util.adb
@@ -1719,6 +1719,31 @@ package body Sem_Util is
             Error_Msg_FE (Msg, N, Typ);
          end if;
 
+         --  Suggest to use First_Valid/Last_Valid instead of First/Last/Range
+         --  if the predicate is static.
+
+         if not Has_Dynamic_Predicate_Aspect (Typ)
+           and then Has_Static_Predicate (Typ)
+           and then Nkind (N) = N_Attribute_Reference
+         then
+            declare
+               Aname   : constant Name_Id := Attribute_Name (N);
+               Attr_Id : constant Attribute_Id := Get_Attribute_Id (Aname);
+            begin
+               case Attr_Id is
+                  when Attribute_First =>
+                     Error_Msg_F ("\use attribute First_Valid instead", N);
+                  when Attribute_Last =>
+                     Error_Msg_F ("\use attribute Last_Valid instead", N);
+                  when Attribute_Range =>
+                     Error_Msg_F ("\use attributes First_Valid and "
+                                  & "Last_Valid instead", N);
+                  when others =>
+                     null;
+               end case;
+            end;
+         end if;
+
          --  Emit an optional suggestion on how to remedy the error if the
          --  context warrants it.