Fortran array signature does not accept array that is both F and C contiguous

[NicolasHug]

Reporting a bug

• I am using the latest released version of Numba (most recent is visible in
  the change log (https://github.com/numba/numba/blob/master/CHANGE_LOG).
• I have included below a minimal working reproducer (if you are unsure how
  to write one see http://matthewrocklin.com/blog/work/2018/02/28/minimal-bug-reports).

I'm not sure if that is a bug or a feature, but passing a 2D array that is both Fortran and C contiguous will fail if the signature expected a Fortran-aligned array:

from numba import jitclass, uint8
import numpy as np

@jitclass([
    ('X', uint8[::1, :]),  # fortran aligned array
])
class Class:
    def __init__(self, X):
        self.X = X

# F contiguous, not C contiguous
X = np.arange(10).reshape(2, 5).astype(np.uint8)
X = np.asfortranarray(X)
assert not X.flags['C_CONTIGUOUS']
assert X.flags['F_CONTIGUOUS']
Class(X)  # OK

X = np.arange(10).reshape(10, 1).astype(np.uint8)
assert X.flags['C_CONTIGUOUS']
assert X.flags['F_CONTIGUOUS']
Class(X)  # fails

Traceback (most recent call last):
  File "numba_lol.py", line 21, in <module>
    Class(X)  # fails
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/jitclass/base.py", line 123, in __call__
    return cls._ctor(*args, **kwargs)
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/dispatcher.py", line 348, in _compile_for_args
    error_rewrite(e, 'typing')
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/dispatcher.py", line 315, in error_rewrite
    reraise(type(e), e, None)
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/six.py", line 658, in reraise
    raise value.with_traceback(tb)
numba.errors.TypingError: Failed in nopython mode pipeline (step: nopython frontend)
Internal error at <numba.typeinfer.CallConstraint object at 0x7fe5fa702160>:
--%<----------------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/errors.py", line 599, in new_error_context
    yield
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/lowering.py", line 254, in lower_block
    self.lower_inst(inst)
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/lowering.py", line 393, in lower_inst
    signature.args[1])
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/targets/base.py", line 677, in cast
    return impl(self, builder, fromty, toty, val)
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/targets/arrayobj.py", line 4673, in array_to_array
    assert fromty.mutable != toty.mutable or toty.layout == 'A'
AssertionError

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/typeinfer.py", line 142, in propagate
    constraint(typeinfer)
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/typeinfer.py", line 423, in __call__
    self.resolve(typeinfer, typevars, fnty)
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/typeinfer.py", line 450, in resolve
    literals=literals)
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/typeinfer.py", line 1173, in resolve_call
    literals=literals)
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/typing/context.py", line 211, in resolve_function_type
    return func.get_call_type_with_literals(self, args, kws, literals)
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/types/abstract.py", line 268, in get_call_type_with_literals
    return self.get_call_type(context, args, kws)
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/types/misc.py", line 375, in get_call_type
    return self.ctor_template(context).apply(args, kws)
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/typing/templates.py", line 207, in apply
    sig = generic(args, kws)
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/jitclass/base.py", line 240, in generic
    sig = disp_type.get_call_type(self.context, boundargs, kws)
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/types/functions.py", line 258, in get_call_type
    template, pysig, args, kws = self.dispatcher.get_call_template(args, kws)
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/dispatcher.py", line 272, in get_call_template
    self.compile(tuple(args))
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/compiler_lock.py", line 32, in _acquire_compile_lock
    return func(*args, **kwargs)
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/dispatcher.py", line 655, in compile
    cres = self._compiler.compile(args, return_type)
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/dispatcher.py", line 82, in compile
    pipeline_class=self.pipeline_class)
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/compiler.py", line 904, in compile_extra
    return pipeline.compile_extra(func)
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/compiler.py", line 367, in compile_extra
    return self._compile_bytecode()
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/compiler.py", line 835, in _compile_bytecode
    return self._compile_core()
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/compiler.py", line 822, in _compile_core
    res = pm.run(self.status)
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/compiler_lock.py", line 32, in _acquire_compile_lock
    return func(*args, **kwargs)
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/compiler.py", line 253, in run
    raise patched_exception
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/compiler.py", line 244, in run
    stage()
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/compiler.py", line 696, in stage_nopython_backend
    self._backend(lowerfn, objectmode=False)
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/compiler.py", line 646, in _backend
    lowered = lowerfn()
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/compiler.py", line 633, in backend_nopython_mode
    self.flags)
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/compiler.py", line 1023, in native_lowering_stage
    lower.lower()
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/lowering.py", line 173, in lower
    self.lower_normal_function(self.fndesc)
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/lowering.py", line 214, in lower_normal_function
    entry_block_tail = self.lower_function_body()
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/lowering.py", line 239, in lower_function_body
    self.lower_block(block)
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/lowering.py", line 254, in lower_block
    self.lower_inst(inst)
  File "/usr/lib64/python3.7/contextlib.py", line 130, in __exit__
    self.gen.throw(type, value, traceback)
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/errors.py", line 607, in new_error_context
    six.reraise(type(newerr), newerr, tb)
  File "/home/nico/.virtualenvs/pygbm/lib/python3.7/site-packages/numba/six.py", line 659, in reraise
    raise value
numba.errors.LoweringError: Failed in nopython mode pipeline (step: nopython mode backend)


File "numba_lol.py", line 9:
    def __init__(self, X):
        self.X = X
        ^

[1] During: lowering "(self).X = X" at numba_lol.py (9)
[2] During: resolving callee type: jitclass.Class#55644369be18<X:array(uint8, 2d, F)>
[3] During: typing of call at <string> (3)

--%<----------------------------------------------------------------------------

[ogrisel]

I think this is a bug (or a limitation of the type system). As the example shows, being C-contiguous or F-contiguous is not exclusive for numpy arrays.

[stuartarchibald]

Thanks for the report. I think this is a limitation, the typing mech at present requires types inheriting from buffer protocol to have a single layout, one of LAYOUTS = frozenset(['C', 'F', 'CS', 'FS', 'A']), with preference given to C based layouts.

Reproducer with no jitclass:

from numba import njit, float64, typeof
import numpy as np

@njit([float64(float64[::1, :]),])
def foo(x):
    return x[0, 0]

# F contiguous, not C contiguous
X = np.arange(10.).reshape(2, 5)
X = np.asfortranarray(X)
print(typeof(X))
assert not X.flags['C_CONTIGUOUS']
assert X.flags['F_CONTIGUOUS']
foo(X)  # OK

X = np.arange(10.).reshape(10, 1)
print(typeof(X))
assert X.flags['C_CONTIGUOUS']
assert X.flags['F_CONTIGUOUS']
foo(X)  # fails