Automatic reallocation failed

[harperjf]

In this program the second assignment to x requires x to be reallocated because its shape has changed.

  integer,allocatable:: x(:)
  x = [1,2,3,4]
  print "(*(1X,I0))",x
  x = [5,6]
  print "(*(1X,I0))",x
end program

Lfortran 0.42.0 output:

Segmentation fault (core dumped)

Four other compilers gave this output, which IMHO is correct:

 1 2 3 4
 5 6

[harperjf]

As #5707 seemed to require the absence of a program statement I tried adding one to my little program, making it read

program test
  integer,allocatable:: x(:)
  x = [1,2,3,4]
  print "(*(1X,I0))",x
  x = [5,6]
  print "(*(1X,I0))",x
end program

Same output as before.

[kmr-srbh]

We do not support implicit allocation by default. You can do so using the --realloc-lhs option.

(base) saurabh-kumar@Awadh:~/Projects/System/lfortran$ lfortran test.f90 --realloc-lhs
 1
 2
 3
 4

 5
 6

[harperjf]

I tried using --realloc-lhs and got @kmr-srbh's output. That proves a bug in lfortran: printing each number on a separate line when the format asked for the whole array x to be printed on one line.

[kmr-srbh]

@harperjf yes, I think we have some ongoing work to fix printing.

[assem2002]

the printing issue should be fixed by #5039.

[harperjf]

Having been misled by assuming that the --std=f23 option would enforce compliance with the Fortran standard I suggest that using that option should automatically use all the other options that make lfortran accept programs that comply with the standard, whether or not they agree with the opinions of lfortran's developers on what is good practice. I think the relevant options are

--realloc-lhs 
--use-loop-variable-after-loop 
--implicit-typing
--implicit-interface

but I may have missed some, or included some that would allow a non-conforming program.
If that is unacceptable to the developers I suggest that those options and --std=f23 be included in a new option, possibly called --STD=f23

[certik]

Yes, that's a bug to not include all standard conforming options. Here are the current options: https://github.com/lfortran/lfortran/blob/main/src/bin/lfortran.cpp#L2336, the implicit ones are already enabled, so just the --realloc-lhs must be added, and also --use-loop-variable-after-loop (if it is conforming).