[Bug ada/126379] New: 'Value Compilation Failure When Given a 2-Parameter Function Argument

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126379

            Bug ID: 126379
           Summary: 'Value Compilation Failure When Given a 2-Parameter
                    Function Argument
           Product: gcc
           Version: 16.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: ada
          Assignee: unassigned at gcc dot gnu.org
          Reporter: efmavourneen at axioaction dot org
                CC: dkm at gcc dot gnu.org
  Target Milestone: ---

GNAT incorrectly rejects a scalar 'Value attribute when its String argument is
supplied directly by a two-parameter function call, reporting “too many
arguments in call to Value_Enumeration_8”. Assigning the identical function
result to an intermediate `String` constant and passing that constant to 'Value
compiles successfully.

----------

--
--  Tick_Value_Compilation_Failure
--
--  Minimal reproducer for scalar 'Value when its String argument is supplied
directly by a function having two
--  parameters.  GNAT 16.1.0 incorrectly reports too many arguments in the
generated call to Value_Enumeration_8.
--

procedure Tick_Value_Compilation_Failure is

   type Selection is
     (First,
      Second);

   function Next_Value (Text     : String;
                        Position : in out Positive) return String;

   function Next_Value (Text     : String;
                        Position : in out Positive) return String is
   begin
      Position := Position + 1;
      return Text;
   end Next_Value;

   Position : Positive := 1;
   Value    : constant Selection := Selection'Value (Next_Value ("First",
Position));

begin

   if Value /= First then --  The compiler defect prevents execution from
reaching this consistency check.
      raise Program_Error;
   end if;

end Tick_Value_Compilation_Failure;

----------

--
--  Tick_Value_Workaround
--
--  Companion to Tick_Value_Compilation_Failure.  Constraining the function
result in a String object before applying
--  scalar 'Value avoids the GNAT 16.1.0 expansion defect.
--

procedure Tick_Value_Workaround is

   type Selection is
     (First,
      Second);

   function Next_Value (Text     : String;
                        Position : in out Positive) return String;

   function Next_Value (Text     : String;
                        Position : in out Positive) return String is
   begin
      Position := Position + 1;
      return Text;
   end Next_Value;

   Position    : Positive := 1;
   Value_Image : constant String := Next_Value ("First", Position);
   Value       : constant Selection := Selection'Value (Value_Image);

begin

   if Value /= First then --  Confirm that the workaround preserves the
intended value.
      raise Program_Error;
   end if;

end Tick_Value_Workaround;