[Bug fortran/65684] New: Wrong error message when writing to a string

[Bug fortran/65684] New: Wrong error message when writing to a string

[a.vogt at fulguritus dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65684

            Bug ID: 65684
           Summary: Wrong error message when writing to a string
           Product: gcc
           Version: 4.9.3
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: a.vogt at fulguritus dot com

gfortran gives the wrong output when writing to a string that is too short: 

Compiling and running this snippet

program test
  implicit none
  character(2) :: str

  write(str,*) 100

  print *, str
end program


results in 
> At line 5 of file test.F90
> Fortran runtime error: End of record

ifort, on the other hand, gives the correct error message: 

> forrtl: severe (66): output statement overflows record, unit -5, file Internal List-Directed Write

Could the gfortran error message be adjusted?

[Bug fortran/65684] Wrong error message when writing to a string

[a.vogt at fulguritus dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65684

--- Comment #1 from Alexander Vogt <a.vogt at fulguritus dot com> ---
This is motivated by this post on Stack Overflow: 
https://stackoverflow.com/questions/29489388/fortran-end-of-record-error-when-saving-a-variable/29490374#29490374

[Bug fortran/65684] Wrong error message when writing to a string

[kargl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65684

kargl at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |kargl at gcc dot gnu.org

--- Comment #2 from kargl at gcc dot gnu.org ---
Your program is non-conforming.  Technically, gfortran can
do anything.  This includes not issuing any error message,
starting World War III, or issuing an error message.  In fact,
gfortran's error message is correct to extent that the write
statement reaches the end-of-record.  

If one takes the time to wander through the final committee
draft of the Fortran 2008 standard, then one can piece together
the story.  The crucial text is the third bullet under Sec. 9.4.

   9.2 Records

   9.2.1 General

   A record is a sequence of values or a sequence of characters.

   9.4 Internal files

   An internal file is a record file with the following properties.

   * A record of an internal file is a scalar character variable.

   * If the file is a scalar character variable, it consists of a
     single record whose length is the same as the length of the
     scalar character variable.

   * A record of the internal file becomes defined by writing the
     record.  If the number of characters written in a record is
     less than the length of the record, the remaining portion of
     the record is filled with blanks.  The number of characters
     to be written shall not exceed the length of the record.

   9.6.4 Execution of a data transfer input/output statement

   9.6.4.1 General
   ....
   (7)  Determine whether an error, end-of-file, or end-of-record
        condition has occurred.
   ....
   (10) If an error, end-of-file, or end-of-record condition occurred,
        processing continues as specified in 9.11; otherwise any
        variable specified in an IOSTAT= specifier is assigned the
        value zero.

   9.11.4 End-of-record condition and the EOR= specifier

   If an end-of-record condition occurs during execution of an
   input/output statement that contains neither an EOR= specifier
   nor an IOSTAT= specifier, error termination is initiated.

IMNSHO, this bug report should be closed as WONTFIX, but I'll
leave it open until others have a chance to comment.

[Bug fortran/65684] Wrong error message when writing to a string

[a.vogt at fulguritus dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65684

--- Comment #3 from Alexander Vogt <a.vogt at fulguritus dot com> ---
OK, I agree that the behavior is Standard conforming... 
Thanks for the clarification! 

Still, the error message issued is not really helpful if one is unfamiliar with
the Standard. Maybe it could be improved for more guidance (point towards the
overflow and maybe the Standard).

[Bug fortran/65684] Wrong error message when writing to a string

[jvdelisle at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65684

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jvdelisle at gcc dot gnu.org
           Assignee|unassigned at gcc dot gnu.org      |jvdelisle at gcc dot gnu.org
           Severity|minor                       |enhancement

--- Comment #4 from Jerry DeLisle <jvdelisle at gcc dot gnu.org> ---
I agree we have no concern over compliance of gfortran here and the error
message is accurate.  So this is not a bug, but a request to enhance the error
message in the case of the writing to a string. So, under the principle of
being helpful to users, I will be willing to do this. It will have to wait
until after the next release happens.

[Bug fortran/65684] Wrong error message when writing to a string

[dominiq at lps dot ens.fr]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65684

Dominique d'Humieres <dominiq at lps dot ens.fr> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-04-08
     Ever confirmed|0                           |1

--- Comment #5 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
Honestly, do you really find that

> forrtl: severe (66): output statement overflows record, unit -5,
> file Internal List-Directed Write

is more helpful than

> At line 5 of file test.F90
> Fortran runtime error: End of record

?

Personally I don't. fortran directs the user to the line and file leading to
the run time error, then if the user does not understand what's wrong with
'write(str,*) 100', (s)he must really learn elementary Fortran.

> I agree we have no concern over compliance of gfortran here and the error
> message is accurate.  So this is not a bug, but a request to enhance the error
> message in the case of the writing to a string. So, under the principle of
> being helpful to users, I will be willing to do this. It will have to wait
> until after the next release happens.

Several months ago I have browsed the bug list for fortran, libfortran (817
entries today) and I have seen about three dozens entries containing "message"
in their summary. I think a fraction of them are more urgent/easy to fix than
this one.

Now, if you really think this PR is important, nothing prevents you to submit a
patch!

[Bug fortran/65684] Wrong error message when writing to a string

[a.vogt at fulguritus dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65684

--- Comment #6 from Alexander Vogt <a.vogt at fulguritus dot com> ---
Fair enough... I have no experience in coding for GCC. Could you give me a hint
where (which file) to start? 

I would propose a message like

> At line 5 of file test.F90
> Fortran runtime error: End of record (number of characters to be written exceeds the length of the record)

[Bug fortran/65684] Wrong error message when writing to a string

[dominiq at lps dot ens.fr]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65684

--- Comment #7 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
> Fair enough... I have no experience in coding for GCC. Could you give me
> a hint where (which file) to start? 

The content of the message is set by 'translate_error (int code)' (line 412 of
libgfortran/runtime/error.c).

> I would propose a message like
>
> > At line 5 of file test.F90
> > Fortran runtime error: End of record (number of characters to be written
> > exceeds the length of the record)

I did not looked further to the code (you can grep for LIBERROR_EOR
libgfortran/runtime/* libgfortran/io/*, and gcc/fortran/* to find where it is
set) but I am not sure that "End of record" cannot be emitted when reading or
for unformatted files. If so your message will be misleading.

[Bug fortran/65684] Wrong error message when writing to a string

[a.vogt at fulguritus dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65684

--- Comment #9 from Alexander Vogt <a.vogt at fulguritus dot com> ---
Then, it would be as simple as passing generate_error the message instead of
NULL.

[Bug fortran/65684] Wrong error message when writing to a string

[a.vogt at fulguritus dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65684

--- Comment #10 from Alexander Vogt <a.vogt at fulguritus dot com> ---
Created attachment 35263
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35263&action=edit
Patch for more specific error messages

This is a suggestion for more verbose error messages... What do you think?

[Bug fortran/65684] Wrong error message when writing to a string

[jvdelisle at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65684

--- Comment #12 from Jerry DeLisle <jvdelisle at gcc dot gnu.org> ---
I have another idea in mind, however I see what your aiming for.  I sense some
frustration over personal preferences and wording and such. There is no rush
here, since we have to wait for next stage 1 regardless.

[Bug fortran/65684] Wrong error message when writing to a string

[jvdelisle at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65684

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |WONTFIX

--- Comment #13 from Jerry DeLisle <jvdelisle at gcc dot gnu.org> ---
After giving this some consideration and with respect, I have decided to close
this as "WONtFIX".  We have standardized the error messages in runtime/error.c
for probably over 10 years now and I think its best to leave it alone.