Support Pythran shape (GH-3307)

* Support Pythran shape

Through a conversion to array. I've tested that and it's ok performance wise,
the C++ compiler can deal with the abstraction (with a small overhead though).

Cython/Compiler/PyrexTypes.py

@@ -1556,7 +1556,13 @@ class PythranExpr(CType):
             self.scope = scope = Symtab.CClassScope('', None, visibility="extern")
             scope.parent_type = self
             scope.directives = {}
-            scope.declare_var("shape", CPtrType(c_long_type), None, cname="_shape", is_cdef=True)
+            shape = scope.declare_cgetter(
+                "shape",
+                CPtrType(c_long_type),
+                pos=None,
+                cname="__Pyx_PythranShapeAccessor",
+                visibility="extern",
+                nogil=True)
             scope.declare_var("ndim", c_long_type, None, cname="value", is_cdef=True)
 
         return True

Cython/Compiler/Symtab.py

@@ -855,6 +855,23 @@ class Scope(object):
         type.entry = entry
         return entry
 
+    def declare_cgetter(self, name, return_type, pos=None, cname=None,
+                        visibility="private", modifiers=(), defining=False, **cfunc_type_config):
+        assert all(
+            k in ('exception_value', 'exception_check', 'nogil', 'with_gil', 'is_const_method', 'is_static_method')
+            for k in cfunc_type_config
+        )
+        cfunc_type = PyrexTypes.CFuncType(
+            return_type,
+            [PyrexTypes.CFuncTypeArg("self", self.parent_type, None)],
+            **cfunc_type_config)
+        entry = self.declare_cfunction(
+            name, cfunc_type, pos, cname=None, visibility=visibility, modifiers=modifiers, defining=defining)
+        entry.is_cgetter = True
+        if cname is not None:
+            entry.func_cname = cname
+        return entry
+
     def add_cfunction(self, name, type, pos, cname, visibility, modifiers,
                       inherited=False):
         # Add a C function entry without giving it a func_cname.

Cython/Utility/CppSupport.cpp

@@ -56,3 +56,5 @@ auto __Pyx_pythran_to_python(T &&value) -> decltype(to_python(
   using returnable_type = typename pythonic::returnable<typename std::remove_cv<typename std::remove_reference<T>::type>::type>::type;
   return to_python(returnable_type{std::forward<T>(value)});
 }
+
+#define __Pyx_PythranShapeAccessor(x) (x.shape().array())

tests/run/numpy_pythran.pyx

@@ -55,3 +55,13 @@ def calculate_tax(cnp.ndarray[double, ndim=1] d):
         np.sum(seg3 * prog_seg3 + 939.57) +
         np.sum(seg4 * prog_seg4)
     ) / np.sum(d)
+
+def access_shape():
+    """
+    >>> access_shape()
+    10
+    """
+    cdef cnp.ndarray[double, ndim=2, mode='c'] array_in = \
+                    1e10 * np.ones((10, 10))
+
+    return array_in.shape[0]