Re-allow copy assignments from const memory views into read/write memory views.

Cython/Compiler/PyrexTypes.py

@@ -782,8 +782,8 @@ class MemoryViewSliceType(PyrexType):
 
         src = self
 
-        if self.writable_needed and not dst.writable_needed:
-            return False
+        #if not copying and self.writable_needed and not dst.writable_needed:
+        #    return False
 
         src_dtype, dst_dtype = src.dtype, dst.dtype
         if dst_dtype.is_const:
@@ -792,6 +792,9 @@ class MemoryViewSliceType(PyrexType):
             if src_dtype.is_const:
                 # When assigning between read-only views, compare only the non-const base types.
                 src_dtype = src_dtype.const_base_type
+        elif copying and src_dtype.is_const:
+            # Copying by value => ignore const on source.
+            src_dtype = src_dtype.const_base_type
 
         if src_dtype != dst_dtype:
             return False

tests/memoryview/numpy_memoryview_readonly.pyx

@@ -88,3 +88,25 @@ def test_const_mmview_ro(x):
     x.setflags(write=False)
     assert x.flags.writeable is False
     return getconst(x)
+
+
+def test_two_views(x):
+    """
+    >>> test_two_views(new_array())
+    23.0
+    """
+    cdef double[:] rw = x
+    cdef const double[:] ro = rw
+    rw[0] = 23
+    return ro[0]
+
+
+def test_assign_ro_to_rw(x):
+    """
+    >>> test_assign_ro_to_rw(new_array())
+    2.0
+    """
+    cdef const double[:] ro = x
+    cdef double[:] rw = np.empty_like(ro)
+    rw[:] = ro
+    return rw[2]