Re: Odd Behaviour

[Mark Wilson <markwilson@wilsonnet.technology>]

On Tuesday, January 18, 2022 at 12:18:56 PM UTC, Mark Wilson wrote:
> On Tuesday, January 18, 2022 at 12:08:16 PM UTC, Mark Wilson wrote: 
> > On Tuesday, January 18, 2022 at 11:51:36 AM UTC, Mark Wilson wrote: 
> > > On Tuesday, January 18, 2022 at 11:48:23 AM UTC, Jeffrey R.Carter wrote: 
> > > > On 2022-01-18 12:05, Mark Wilson wrote: 
> > > > > 
> > > > > then an error is raised: 'warning: Valued_Procedure has no effect for convention Ada [enabled by default]' 
> > > > The GNAT RM says of pragma Import_Valued_Procedure 
> > > > 
> > > > "Note that it is important to use this pragma in conjunction with a separate 
> > > > pragma Import that specifies the desired convention, since otherwise the default 
> > > > convention is Ada, which is almost certainly not what is required." 
> > > > 
> > > > What happens if you replace the import aspects with pragma Import? 
> > > > -- 
> > > > Jeff Carter 
> > > > "Monsieur Arthur King, who has the brain of a duck, you know." 
> > > > Monty Python & the Holy Grail 
> > > > 09 
> > > Tried pragma Import, and even pragma Convention, so, for instance, 
> > > procedure SQLAllocHandle 
> > > (Result : out SQLRETURN; 
> > > HandleType : in SQL_HANDLE_TYPE; 
> > > InputHandle : in SQLHANDLE; 
> > > OutputHandlePtr : in out SQLHANDLE) 
> > > with 
> > > Pre => (Handletype = SQL_Handle_Env); 
> > > 
> > > pragma Import (C, SQLAllocHandle, "SQLAllocHandle"); 
> > > pragma Import_Valued_Procedure (SQLAllocHandle); 
> > > 
> > > Fails with the same warning. Take the 'pre' out and it works fine. 
> > Even tried (which to be fair is a bit of a long shot), 
> > procedure SQLAllocHandle 
> > (Result : out SQLRETURN; 
> > HandleType : in SQL_HANDLE_TYPE; 
> > InputHandle : in SQLHANDLE; 
> > OutputHandlePtr : in out SQLHANDLE); 
> > -- with 
> > -- Pre => (Handletype = SQL_Handle_Env); 
> > 
> > 
> > pragma Import (C, SQLAllocHandle); 
> > pragma Import_Valued_Procedure 
> > (SQLAllocHandle, "SQLAllocHandle", 
> > (SQLRETURN, SQL_HANDLE_TYPE, SQLHANDLE, SQLHANDLE), 
> > (Reference, Value, Value, Reference)); 
> > 
> > Do you think I should file a bug report?
> Well, this works - but feels very naughty, 
> 
> function SQLAllocHandle 
> (HandleType : in SQL_HANDLE_TYPE; 
> InputHandle : in SQLHANDLE; 
> OutputHandlePtr : in SQLHANDLE) 
> return SQLRETURN;
> -- with 
> -- Pre => (Handletype = SQL_Handle_Env); 
> 
> pragma Import (C, SQLAllocHandle);
> pragma Import_Function 
> (SQLAllocHandle, "SQLAllocHandle", 
> (SQL_HANDLE_TYPE, SQLHANDLE, SQLHANDLE), SQLRETURN, 
> (Value, Value, Reference)); 
> 
> However, adding the precondition in results in '<artificial>:(.text+0xb7): undefined reference to `sqlallochandle'''

This works!

   function SQLAllocHandle
     (HandleType      : in     SQL_HANDLE_TYPE;
      InputHandle     : in     SQLHANDLE;
      OutputHandlePtr : in SQLHANDLE)
     return SQLRETURN
   with
     Pre =>   (Handletype = SQL_Handle_Env);
   
   pragma Import (C, SQLAllocHandle, "SQLAllocHandle");
   
   pragma Import_Function
     (SQLAllocHandle, "SQLAllocHandle",
      (SQL_HANDLE_TYPE, SQLHANDLE, SQLHANDLE), SQLRETURN,
      (Value, Value, Reference));

(so specified the external function name in the Import as well as the Import_Function)

Even the writing to an 'in' parameter worked,

   Result := SQLAllocHandle
     (HandleType      => SQL_HANDLE_ENV,
      InputHandle     => SQL_NULL_HANDLE,
      OutputHandlePtr => SQLHANDLE (Handle));
   
   Put_Line (SQLRETURN'Image (Result));
   Put_Line (Boolean'Image (SQLHANDLE(Handle) /= SQL_NULL_HANDLE));

The first Put_Line returns SQL_SUCCESS, and the second returns TRUE

Ugly as hell, though. Spark complains,

odbc.ads:100:04: warning: pragma "IMPORT_FUNCTION" ignored (not yet supported)
odbc.ads:139:04: warning: pragma "IMPORT_VALUED_PROCEDURE" ignored (not yet supported),

and there's the horrible Ada warning that,

main.adb:10:04: warning: variable "Handle" is read but never assigned [-gnatwv]

I think it is going to be much cleaner (and clearer) to abstract this away to an Ada body.