[Bug fortran/107068] New: Run-time error when reading logical arrays with a namelist

[Bug fortran/107068] New: Run-time error when reading logical arrays with a namelist

[r.m.potvliege at durham dot ac.uk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107068

            Bug ID: 107068
           Summary: Run-time error when reading logical arrays with a
                    namelist
           Product: gcc
           Version: 11.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: r.m.potvliege at durham dot ac.uk
  Target Milestone: ---

[Bug fortran/107068] Run-time error when reading logical arrays with a namelist

[r.m.potvliege at durham dot ac.uk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107068

--- Comment #1 from Robert Potvliege <r.m.potvliege at durham dot ac.uk> ---
Reading a logical array through a namelist triggers an (apparently) spurious
run time error in some cases. E.g., when I am compiling the following code with
gfortran,

      program test
      logical, dimension(3,3) :: flc,flp
      namelist/inputdata/flc,flp
!
      read(5,inputdata)
!
      end program test

and read the following file,

&INPUTDATA
 FLC = T,
 FLP(1,2) = T,
/

the execution stops with the error message

At line 5 of file progtest.f90 (unit = 5, file = 'stdin')
Fortran runtime error: Bad repeat count in item 1 of list input

However, there is no error for the following input file

&INPUTDATA
 FLC = T,
 FLP = T,
/

or the following one

&INPUTDATA
 FLP(1,2) = T,
/

etc. No error is produced for any of these input files if I compile this short
program with the Intel compiler I can access rather than gfortran.

[Bug libfortran/107068] Run-time error when reading logical arrays with a namelist

[anlauf at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107068

anlauf at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
          Component|fortran                     |libfortran
   Last reconfirmed|                            |2022-09-28

--- Comment #2 from anlauf at gcc dot gnu.org ---
Confirmed.

Renaming the second variable (e.g. flp -> xlp) works around the problem,
as well as interchanging the lines in the namelist input.

It appears that while scanning the namelist input we first see the T,
then F, for which we try to determine if it means .false. or is part of
a variable name, and then possibly screw up because we see a comma when
referring to an element of rank-2 array flp.

There is also no error when using a rank-1 array for flp and referring
to flp(2) etc.

[Bug libfortran/107068] Run-time error when reading logical arrays with a namelist

[r.m.potvliege at durham dot ac.uk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107068

--- Comment #3 from Robert Potvliege <r.m.potvliege at durham dot ac.uk> ---
Thanks for looking into this so quickly and for the work-round.

[Bug libfortran/107068] Run-time error when reading logical arrays with a namelist

[r.m.potvliege at durham dot ac.uk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107068

--- Comment #4 from Robert Potvliege <r.m.potvliege at durham dot ac.uk> ---
Thanks for looking into this so quickly and for the work-round.

[Bug libfortran/107068] Run-time error when reading logical arrays with a namelist

[jvdelisle at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107068

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

--- Comment #5 from Jerry DeLisle <jvdelisle at gcc dot gnu.org> ---
I will get looking at this since it is namelist related.

[Bug libfortran/107068] Run-time error when reading logical arrays with a namelist

[jvdelisle at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107068

--- Comment #6 from Jerry DeLisle <jvdelisle at gcc dot gnu.org> ---
What is happening here is that in the name list input, the variable flp is also
a legal LOGICAL value, so our read is interpreting it as the second value of
the array flc and trying to continue to read values for flc. It encounters the
( and throws the error.

To resolve this, I think I will have to check for a valid variable name for
each value.

[aside: A lot of these issues stem from the weaknesses in how namelists are
interpreted.  There are ambiguities in the specification.]

My next step here is to go through the F2018 standard just to make sure what we
do is valid or invalid. (cheers)

[Bug libfortran/107068] Run-time error when reading logical arrays with a namelist

[jvdelisle at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107068

--- Comment #7 from Jerry DeLisle <jvdelisle at gcc dot gnu.org> ---
In list_read.c we have this comment:

/* To read a logical we have to look ahead in the input stream to make sure
    there is not an equal sign indicating a variable name.  To do this we use
    line_buffer to point to a temporary buffer, pushing characters there for
    possible later reading. */

I remember creating this line_buffer for the purpose. Now to figure out why it
is not working. This was quite a while ago!

[Bug libfortran/107068] Run-time error when reading logical arrays with a namelist

[jvdelisle at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107068

--- Comment #8 from Jerry DeLisle <jvdelisle at gcc dot gnu.org> ---
After a bit of sleuthing it turns out that the '(' in the name was being
ignored and the comma in '(1,2)' was being treated as a delimiter.  Since the
following '=' was not seen yet, the 2 was seen as a repeat value and we get the
error.

This is fixed with the following patch:

diff --git a/libgfortran/io/list_read.c b/libgfortran/io/list_read.c
index f8ca64422de..0b7884fdda7 100644
--- a/libgfortran/io/list_read.c
+++ b/libgfortran/io/list_read.c
@@ -888,6 +888,14 @@ read_logical (st_parameter_dt *dtp, int length)
   for(i = 0; i < 63; i++)
     {
       c = next_char (dtp);
+      if (c == '(')
+       {
+         l_push_char (dtp, c);
+         dtp->u.p.nml_read_error = 1;
+         dtp->u.p.line_buffer_enabled = 1;
+         dtp->u.p.line_buffer_pos = 0;
+         return;
+       }
       if (is_separator(c))
        {
          /* All done if this is not a namelist read.  */

[Bug libfortran/107068] Run-time error when reading logical arrays with a namelist

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107068

--- Comment #9 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jerry DeLisle <jvdelisle@gcc.gnu.org>:

https://gcc.gnu.org/g:fccfe6625121512f247cb59888e50eb9dcc84409

commit r14-9048-gfccfe6625121512f247cb59888e50eb9dcc84409
Author: Jerry DeLisle <jvdelisle@gcc.gnu.org>
Date:   Fri Feb 16 17:06:37 2024 -0800

    libgfortran: Fix namelist read.

            PR libfortran/107068

    libgfortran/ChangeLog:

            * io/list_read.c (read_logical): When looking for a possible
            variable name, check for left paren, indicating a possible
            array reference.

    gcc/testsuite/ChangeLog:

            * gfortran.dg/pr107068.f90: New test.

[Bug libfortran/107068] Run-time error when reading logical arrays with a namelist

[jvdelisle at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107068

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

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

--- Comment #10 from Jerry DeLisle <jvdelisle at gcc dot gnu.org> ---
Fixed on trunk. Closing.