[Bug libfortran/124668] STOP statement should probably flush OUTPUT_UNIT before issuing its message on ERROR_UNIT

[jvdelisle at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124668

Jerry DeLisle <jvdelisle at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2026-03-29
                 CC|                            |jvdelisle at gcc dot gnu.org
             Status|UNCONFIRMED                 |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |jvdelisle at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #8 from Jerry DeLisle <jvdelisle at gcc dot gnu.org> ---
(In reply to Steve Kargl from comment #7)
> (In reply to Walter Spector from comment #6)
> 
> > One can work around the problem by placing a FLUSH (OUTPUT_UNIT) statement
> > just prior to the STOP.  But this seems silly.

It seems we do not have a concensus about whether this is a problem or not.

> 
> Seems like good defensive programming as stdout and stdin
> are the same "external file" (i.e., device).
> 
> And as already mentions, there are two environmental 
> variables available to control buffering.

I did compare to flang and intel compilers and their behaviour agrees with
Walter. The following trivial patch seems to do it. I also regression tested it
and all is good. I would prefer to wait for after the 16 release if we do this.

diff --git a/libgfortran/runtime/stop.c b/libgfortran/runtime/stop.c
index 9be1b4b83ea..1b22cec040e 100644
--- a/libgfortran/runtime/stop.c
+++ b/libgfortran/runtime/stop.c
@@ -124,6 +124,7 @@ stop_numeric (int code, bool quiet)
   if (!quiet)
     {
       report_exception ();
+      flush_all_units ();
       st_printf ("STOP %d\n", code);
     }
   exit (code);
@@ -138,6 +139,7 @@ stop_string (const char *string, size_t len, bool quiet)
   if (!quiet)
     {
       report_exception ();
+      flush_all_units ();
       if (string)
        {
          struct iovec iov[3];
@@ -169,6 +171,7 @@ error_stop_string (const char *string, size_t len, bool
quiet)
     {
       struct iovec iov[3];
       report_exception ();
+      flush_all_units ();
       iov[0].iov_base = (char*) "ERROR STOP ";
       iov[0].iov_len = strlen (iov[0].iov_base);
       iov[1].iov_base = (char*) string;
@@ -192,6 +195,7 @@ error_stop_numeric (int code, bool quiet)
   if (!quiet)
     {
       report_exception ();
+      flush_all_units ();
       st_printf ("ERROR STOP %d\n", code);
     }
   exit_error (code);