BUG: f2py generated signature file and automatic arrays

Describe the issue:

Let’s consider the following subroutine in a test.f90 file that declares an automatic array from two variables(*):

subroutine test (nx, ny, arr)

  implicit none

  integer, intent(in) :: nx
  integer, intent(in) :: ny
  integer, dimension(nx*ny) :: arr

return
end subroutine test

It used to work with numpy 1.22.0 or earlier, despite the Warning: cross-dependence between variables "ny" and "nx" and the weird shape checks as shown in the generated test.pyf signature file below:

!    -*- f90 -*-
! Note: the context of this file is case sensitive.

python module test ! in 
    interface  ! in :test
        subroutine test(nx,ny,arr) ! in :test:src/test.f90
            integer, optional,intent(in),check(shape(arr, 0) == nx * ny),depend(ny,arr) :: nx=shape(arr, 0) / nx
            integer, optional,intent(in),check(shape(arr, 0) == nx * ny),depend(nx,arr) :: ny=shape(arr, 0) / nx
            integer dimension(nx * ny) :: arr
        end subroutine test
    end interface 
end python module test

! This file was auto-generated with f2py (version:1.22.0).
! See:
! https://web.archive.org/web/20140822061353/http://cens.ioc.ee/projects/f2py2e

However, with numpy 1.22.1 or later, it generates a test.pyf with “swapped” nx / ny:

!    -*- f90 -*-
! Note: the context of this file is case sensitive.

python module test ! in 
    interface  ! in :test
        subroutine test(nx,ny,arr) ! in :test:src/test.f90
            integer, optional,intent(in),check(shape(arr, 0) == nx * ny),depend(ny,arr) :: nx=shape(arr, 0) / ny
            integer, optional,intent(in),check(shape(arr, 0) == nx * ny),depend(arr,nx) :: ny=shape(arr, 0) / nx
            integer dimension(nx * ny) :: arr
        end subroutine test
    end interface 
end python module test

! This file was auto-generated with f2py (version:1.22.1).
! See:
! https://web.archive.org/web/20140822061353/http://cens.ioc.ee/projects/f2py2e

Which causes the following recursion error when trying to generate the Python extension from the signature file:

Reading fortran codes...
        Reading file 'test.pyf' (format:free)
Post-processing...
        Block: test
                        Block: test
Traceback (most recent call last):
  File "/Users/me/env/bin/f2py", line 8, in <module>
    sys.exit(main())
  File "/Users/me/env/lib/python3.9/site-packages/numpy/f2py/f2py2e.py", line 693, in main
    run_main(sys.argv[1:])
  File "/Users/me/env/lib/python3.9/site-packages/numpy/f2py/f2py2e.py", line 430, in run_main
    postlist = callcrackfortran(files, options)
  File "/Users/me/env/lib/python3.9/site-packages/numpy/f2py/f2py2e.py", line 333, in callcrackfortran
    postlist = crackfortran.crackfortran(files)
  File "/Users/me/env/lib/python3.9/site-packages/numpy/f2py/crackfortran.py", line 3209, in crackfortran
    postlist = postcrack(grouplist[0])
  File "/Users/me/env/lib/python3.9/site-packages/numpy/f2py/crackfortran.py", line 1926, in postcrack
    g = postcrack(g, tab=tab + '\t')
  File "/Users/me/env/lib/python3.9/site-packages/numpy/f2py/crackfortran.py", line 1945, in postcrack
    block['body'] = analyzebody(block, args, tab=tab)
  File "/Users/me/env/lib/python3.9/site-packages/numpy/f2py/crackfortran.py", line 2107, in analyzebody
    b = postcrack(b, as_, tab=tab + '\t')
  File "/Users/me/env/lib/python3.9/site-packages/numpy/f2py/crackfortran.py", line 1945, in postcrack
    block['body'] = analyzebody(block, args, tab=tab)
  File "/Users/me/env/lib/python3.9/site-packages/numpy/f2py/crackfortran.py", line 2107, in analyzebody
    b = postcrack(b, as_, tab=tab + '\t')
  File "/Users/me/env/lib/python3.9/site-packages/numpy/f2py/crackfortran.py", line 1941, in postcrack
    block['vars'] = analyzevars(block)
  File "/Users/me/env/lib/python3.9/site-packages/numpy/f2py/crackfortran.py", line 2458, in analyzevars
    params = get_parameters(vars, get_useparameters(block))
  File "/Users/me/env/lib/python3.9/site-packages/numpy/f2py/crackfortran.py", line 2329, in get_parameters
    for n in get_sorted_names(vars):
  File "/Users/me/env/lib/python3.9/site-packages/numpy/f2py/crackfortran.py", line 2257, in get_sorted_names
    depend_dict = _calc_depend_dict(vars)
  File "/Users/me/env/lib/python3.9/site-packages/numpy/f2py/crackfortran.py", line 2250, in _calc_depend_dict
    _get_depend_dict(n, vars, depend_dict)
  File "/Users/me/env/lib/python3.9/site-packages/numpy/f2py/crackfortran.py", line 2236, in _get_depend_dict
    or _get_depend_dict(word, vars, deps):
  File "/Users/me/env/lib/python3.9/site-packages/numpy/f2py/crackfortran.py", line 2236, in _get_depend_dict
    or _get_depend_dict(word, vars, deps):
  File "/Users/me/env/lib/python3.9/site-packages/numpy/f2py/crackfortran.py", line 2236, in _get_depend_dict
    or _get_depend_dict(word, vars, deps):
  [Previous line repeated 979 more times]
  File "/Users/me/env/lib/python3.9/site-packages/numpy/f2py/crackfortran.py", line 2228, in _get_depend_dict
    if '=' in vars[name] and not isstring(vars[name]):
  File "/Users/me/env/lib/python3.9/site-packages/numpy/f2py/auxfuncs.py", line 77, in isstring
    return _isstring(var) and not isarray(var)
  File "/Users/me/env/lib/python3.9/site-packages/numpy/f2py/auxfuncs.py", line 72, in _isstring
    return 'typespec' in var and var['typespec'] == 'character' and \
RecursionError: maximum recursion depth exceeded in comparison

The difference between the two generated signature files seems to be a result of #20721.

(*) Do you think the issue here could be considered as a regression? Or is the example here wrong and we should not declare dimensions of automatic arrays from two or more variables? Not sure about this as I’m not a Fortran expert and haven’t found much info about this practice, although I’d be surprised that compilers let us do it if it wasn’t valid.

Reproduce the code example:

# see f90 / pyf source above

Error message:

No response

NumPy/Python version information:

Numpy 1.22.0 / 1.22.1 Python 3.9

[benbovy]

👍 Great thanks!

[charris]

Here is a list of the 21 changed files:

	modified:   numpy/f2py/auxfuncs.py
	modified:   numpy/f2py/capi_maps.py
	modified:   numpy/f2py/cb_rules.py
	modified:   numpy/f2py/cfuncs.py
	modified:   numpy/f2py/common_rules.py
	modified:   numpy/f2py/crackfortran.py
	modified:   numpy/f2py/f90mod_rules.py
	modified:   numpy/f2py/func2subr.py
	modified:   numpy/f2py/rules.py
	modified:   numpy/f2py/src/fortranobject.c
	modified:   numpy/f2py/src/fortranobject.h
	modified:   numpy/f2py/tests/src/array_from_pyobj/wrapmodule.c
	new file:   numpy/f2py/tests/src/crackfortran/pubprivmod.f90
	modified:   numpy/f2py/tests/test_array_from_pyobj.py
	modified:   numpy/f2py/tests/test_callback.py
	new file:   numpy/f2py/tests/test_character.py
	modified:   numpy/f2py/tests/test_crackfortran.py
	new file:   numpy/f2py/tests/test_docs.py
	modified:   numpy/f2py/tests/test_f2py2e.py
	modified:   numpy/f2py/tests/test_return_character.py
	modified:   numpy/f2py/tests/util.py