[Ada] Set related expression for external DISCR symbols in Build_Temporary

[Ada] Set related expression for external DISCR symbols in Build_Temporary

[Pierre-Marie de Rodat]

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This is required for CodePeer to use a better name for a variable, or a
constant created by GNAT.

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

gcc/ada/

	* exp_util.adb (Build_Temporary): In case of an external DISCR
	symbol, set the related expression for CodePeer so that a more
	comprehensible message can be emitted to the user.

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diff --git a/gcc/ada/exp_util.adb b/gcc/ada/exp_util.adb
--- a/gcc/ada/exp_util.adb
+++ b/gcc/ada/exp_util.adb
@@ -11656,6 +11656,7 @@ package body Exp_Util is
       is
          Temp_Id  : Entity_Id;
          Temp_Nam : Name_Id;
+         Should_Set_Related_Expression : Boolean := False;
 
       begin
          --  The context requires an external symbol : expression is
@@ -11675,6 +11676,12 @@ package body Exp_Util is
 
             else
                pragma Assert (Discr_Number > 0);
+
+               --  We don't have any intelligible way of printing T_DISCR in
+               --  CodePeer. Thus, set a related expression in this case.
+
+               Should_Set_Related_Expression := True;
+
                --  Use fully qualified name to avoid ambiguities.
 
                Temp_Nam :=
@@ -11684,6 +11691,10 @@ package body Exp_Util is
 
             Temp_Id := Make_Defining_Identifier (Loc, Temp_Nam);
 
+            if Should_Set_Related_Expression then
+               Set_Related_Expression (Temp_Id, Related_Nod);
+            end if;
+
          --  Otherwise generate an internal temporary
 
          else