Multi-dimensional indexing does not work correctly

[cycomanic]

Split from #1714

I get a compile error when trying to index an array with a tuple.

Example code:

#pythran export indexing(float64[:,:,3], (int[], int[]))
def indexing(img, idx):
    return img[idx]

Compiler error (gcc):

/home/jschrod/PycharmProjects/pythran/pythran/pythonic/include/types/numpy_gexpr.hpp: In instantiation of ‘struct {anonymous}::pythonic::types::numpy_gexpr<{anonymous}::pythonic::types::ndarray<double, {anonymous}::pythonic::types::array_base<long int, 3, {anonymous}::pythonic::types::tuple_version> >, {anonymous}::pythonic::types::contiguous_normalized_slice, {anonymous}::pythonic::types::ndarray<long int, {anonymous}::pythonic::types::pshape<long int> > >’:
/tmp/tmpv6req14z.cpp:42:685:   required from here
/home/jschrod/PycharmProjects/pythran/pythran/pythonic/include/types/numpy_gexpr.hpp:536:71: error: static assertion failed: all slices are valid
  536 |                        std::is_same<S, normalized_slice>::value)...>::value,
      |                                                                       ^~~~~
/home/jschrod/PycharmProjects/pythran/pythran/pythonic/include/types/numpy_gexpr.hpp: In instantiation of ‘constexpr const size_t {anonymous}::pythonic::types::count_long<{anonymous}::pythonic::types::ndarray<long int, {anonymous}::pythonic::types::pshape<long int> > >::value’:
/home/jschrod/PycharmProjects/pythran/pythran/pythonic/include/types/numpy_gexpr.hpp:166:24:   recursively required from ‘constexpr const size_t {anonymous}::pythonic::types::count_long<{anonymous}::pythonic::types::ndarray<long int, {anonymous}::pythonic::types::pshape<long int> > >::value’
/home/jschrod/PycharmProjects/pythran/pythran/pythonic/include/types/numpy_gexpr.hpp:166:24:   required from ‘constexpr const size_t {anonymous}::pythonic::types::count_long<{anonymous}::pythonic::types::ndarray<long int, {anonymous}::pythonic::types::pshape<long int> > >::value’
/home/jschrod/PycharmProjects/pythran/pythran/pythonic/include/types/numpy_gexpr.hpp:166:54:   required from ‘constexpr const size_t {anonymous}::pythonic::types::count_long<{anonymous}::pythonic::types::contiguous_normalized_slice, {anonymous}::pythonic::types::ndarray<long int, {anonymous}::pythonic::types::pshape<long int> > >::value’
/home/jschrod/PycharmProjects/pythran/pythran/pythonic/include/types/numpy_gexpr.hpp:557:69:   required from ‘constexpr const size_t {anonymous}::pythonic::types::numpy_gexpr<{anonymous}::pythonic::types::ndarray<double, {anonymous}::pythonic::types::array_base<long int, 3, {anonymous}::pythonic::types::tuple_version> >, {anonymous}::pythonic::types::contiguous_normalized_slice, {anonymous}::pythonic::types::ndarray<long int, {anonymous}::pythonic::types::pshape<long int> > >::value’
/home/jschrod/PycharmProjects/pythran/pythran/pythonic/include/types/numpy_gexpr.hpp:578:52:   required from ‘struct {anonymous}::pythonic::types::numpy_gexpr<{anonymous}::pythonic::types::ndarray<double, {anonymous}::pythonic::types::array_base<long int, 3, {anonymous}::pythonic::types::tuple_version> >, {anonymous}::pythonic::types::contiguous_normalized_slice, {anonymous}::pythonic::types::ndarray<long int, {anonymous}::pythonic::types::pshape<long int> > >’
/tmp/tmpv6req14z.cpp:42:685:   required from here
/home/jschrod/PycharmProjects/pythran/pythran/pythonic/include/types/numpy_gexpr.hpp:166:24: fatal error: template instantiation depth exceeds maximum of 900 (use ‘-ftemplate-depth=’ to increase the maximum)
  166 |         count_long<T>::value + count_long<Types...>::value;
      |                        ^~~~~
compilation terminated.
WARNING: Compilation error, trying hard to find its origin...
WARNING: Nop, I'm going to flood you with C++ errors!
CRITICAL: Cover me Jack. Jack? Jaaaaack!!!!

Initially I thought this was related to a having only two elements of the tuple for a 3D array, but the following also yields the same error:

#pythran export index2(float64[:,:], (int[],int[]))
def index2(img, idx):
    return img[idx]

[cycomanic]

I suspect that this is the same error as #1664. I can simplify to:

#pythran export draw_line(int64[][], int64[])
def draw_line(grid, x):
    grid[:,x] = 1
    return grid

which results in teh same compile error as above.

On the other hand

#pythran export draw_line(int64[][], int64[])
def draw_line(grid, x):
    grid[x,:] = 1
    return grid

compiles but does not modify grid, so gives an incorrect result.

Finally

#pythran export draw_line(int64[][], int64[])
def draw_line(grid, x):
    grid[x] = 1
    return grid

does the right thing.

I've looked at ~numpy_gexpr.hpp~ but that goes beyond my cpp skillset.