file_utils::input_unit_exist fails if there is a trailing/leading tab in the line

Reported by Rahul Gaur in Slack.

file_utils::input_unit_exist checks if a namelist with a given name exists in the input file. It compares the input to a line in the input file like: trim(adjustl(line)) == "&"//nml. However, because tab characters aren’t considered “blanks” by Fortran, they are not removed by trim.

The following program and inputfile reproduce the problem:

program mvce
  use file_utils
  implicit none
  logical :: list
  integer :: unit
  logical :: fail_exists, pass_exists

  call init_file_utils(list)
  unit = input_unit_exist("fail", fail_exists)
  unit = input_unit_exist("pass", pass_exists)
  print*, fail_exists, pass_exists
end program mvce

&fail   
/
&pass  
/

There is a tab on the fail line and spaces on the pass line.

I guess we also don’t strip comments, so they’re likely to trip things up too.

Note that a trivial workaround exists: use tr -d ‘\t’ to remove all tabs from an input file.

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