[Ada] Fix PR ada/117517

[Eric Botcazou]

This is an internal error on the new Reduce attribute of Ada 2022 when the 
programmer swaps its arguments(!)  The change makes it so that the compiler 
gives an error message instead.

Tested on x86-64/Linux, applied on the mainline and 15 branch.


2025-09-30  Eric Botcazou  <ebotca...@adacore.com>

        PR ada/117517
        * sem_attr.adb (Resolve_Attribute) <Attribute_Reduce>: Try to
        resolve the reducer first.  Fix casing of error message.


2025-09-30  Eric Botcazou  <ebotca...@adacore.com>

        * gnat.dg/reduce1.adb: New test.

-- 
Eric Botcazou
diff --git a/gcc/ada/sem_attr.adb b/gcc/ada/sem_attr.adb
index bde4d40dcb5..e9e245afb60 100644
--- a/gcc/ada/sem_attr.adb
+++ b/gcc/ada/sem_attr.adb
@@ -12851,7 +12851,10 @@ package body Sem_Attr is
                end Proper_Op;
 
             begin
-               Resolve (Init_Value_Exp, Typ);
+               --  First try to resolve the reducer and then, if this succeeds,
+               --  resolve the initial value.  This nicely deals with confused
+               --  programmers who swap the two items.
+
                if Is_Overloaded (Reducer_Subp_Name) then
                   Outer :
                   for Retry in Boolean loop
@@ -12873,14 +12876,18 @@ package body Sem_Attr is
                then
                   Op := Reducer_Subp_Name;
 
-               elsif Proper_Op (Entity (Reducer_Subp_Name)) then
+               elsif Is_Entity_Name (Reducer_Subp_Name)
+                 and then Proper_Op (Entity (Reducer_Subp_Name))
+               then
                   Op := Entity (Reducer_Subp_Name);
                   Set_Etype (N, Typ);
                end if;
 
                if No (Op) then
-                  Error_Msg_N ("No suitable reducer subprogram found",
+                  Error_Msg_N ("no suitable reducer subprogram found",
                     Reducer_Subp_Name);
+               else
+                  Resolve (Init_Value_Exp, Typ);
                end if;
             end;
 

-- { dg-do compile }
-- { dg-options "-gnat2022" }

procedure Reduce1 is

  type Arr is array (Positive range <>) of Positive;

  A: Arr := (2, 87);

  B: Positive := A'Reduce (1, Positive'Max); -- { dg-error "no suitable" }

begin
  null;
end;