enable direct assignments to C arrays by transforming to full slice assignment

Cython/Compiler/ExprNodes.py

@@ -1860,7 +1860,6 @@ class NameNode(AtomicExprNode):
     def is_lvalue(self):
         return (
             self.entry.is_variable and
-            not self.entry.type.is_array and
             not self.entry.is_readonly
         ) or (
             self.entry.is_cfunction and
@@ -11247,7 +11246,7 @@ class CoerceFromPyTypeNode(CoercionNode):
         return self
 
     def is_ephemeral(self):
-        return self.type.is_ptr and self.arg.is_ephemeral()
+        return (self.type.is_ptr and not self.type.is_array) and self.arg.is_ephemeral()
 
     def generate_result_code(self, code):
         code.putln(self.type.from_py_call_code(

Cython/Compiler/Nodes.py

@@ -4750,14 +4750,20 @@ class SingleAssignmentNode(AssignmentNode):
             self.lhs.memslice_broadcast = True
             self.rhs.memslice_broadcast = True
 
-        is_index_node = isinstance(self.lhs, ExprNodes.IndexNode)
-        if (is_index_node and not self.rhs.type.is_memoryviewslice and
-            (self.lhs.memslice_slice or self.lhs.is_memslice_copy) and
-            (self.lhs.type.dtype.assignable_from(self.rhs.type) or
-             self.rhs.type.is_pyobject)):
+        if (self.lhs.is_subscript and not self.rhs.type.is_memoryviewslice and
+                (self.lhs.memslice_slice or self.lhs.is_memslice_copy) and
+                (self.lhs.type.dtype.assignable_from(self.rhs.type) or
+                 self.rhs.type.is_pyobject)):
             # scalar slice assignment
             self.lhs.is_memslice_scalar_assignment = True
             dtype = self.lhs.type.dtype
+        elif self.lhs.type.is_array:
+            if not isinstance(self.lhs, (ExprNodes.IndexNode, ExprNodes.SliceIndexNode)):
+                # cannot assign to C array, only to its full slice
+                self.lhs = ExprNodes.SliceIndexNode(
+                    self.lhs.pos, base=self.lhs, start=None, stop=None)
+                self.lhs = self.lhs.analyse_target_types(env)
+            dtype = self.lhs.type
         else:
             dtype = self.lhs.type
 

tests/run/carray_coercion.pyx

@@ -96,6 +96,21 @@ def to_int_array(x):
     Traceback (most recent call last):
     IndexError: too many values found during array assignment, expected 3
     """
+    cdef int[3] v = x
+    return v[0], v[1], v[2]
+
+
+def to_int_array_slice(x):
+    """
+    >>> to_int_array_slice([1, 2, 3])
+    (1, 2, 3)
+    >>> to_int_array_slice([1, 2])
+    Traceback (most recent call last):
+    IndexError: not enough values found during array assignment, expected 3, got 2
+    >>> to_int_array_slice([1, 2, 3, 4])
+    Traceback (most recent call last):
+    IndexError: too many values found during array assignment, expected 3
+    """
     cdef int[3] v
     v[:] = x[:3]
     assert v[0] == x[0]