make item types of tuple/array unpacking inferable and institutionalise the...

make item types of tuple/array unpacking inferable and institutionalise the IndexNode creation for the inference

Cython/Compiler/ExprNodes.py

@@ -476,6 +476,14 @@ class ExprNode(Node):
         # can't be modified as part of globals or closures.
         return self.is_literal or self.is_temp or self.type.is_array or self.type.is_cfunction
 
+    def inferable_item_node(self, index=0):
+        """
+        Return a node that represents the (type) result of an indexing operation,
+        e.g. for tuple unpacking or iteration.
+        """
+        return IndexNode(self.pos, base=self, index=IntNode(
+            self.pos, value=str(index), constant_result=index, type=PyrexTypes.c_py_ssize_t_type))
+
     # --------------- Type Analysis ------------------
 
     def analyse_as_module(self, env):
@@ -3846,6 +3854,10 @@ class SliceIndexNode(ExprNode):
             return PyrexTypes.c_array_type(base_type.base_type, None)
         return py_object_type
 
+    def inferable_item_node(self, index=0):
+        # slicing shouldn't change the result type of the base
+        return self.base.inferable_item_node(index)
+
     def may_be_none(self):
         base_type = self.base.type
         if base_type:

Cython/Compiler/FlowControl.py

@@ -776,9 +776,9 @@ class ControlFlowAnalysis(CythonTransform):
             if entry is None: # TODO: This shouldn't happen...
                 return
             self.flow.mark_assignment(lhs, rhs, entry)
-        elif isinstance(lhs, ExprNodes.SequenceNode):
-            for arg in lhs.args:
-                self.mark_assignment(arg)
+        elif lhs.is_sequence_constructor:
+            for i, arg in enumerate(lhs.args):
+                self.mark_assignment(arg, rhs.inferable_item_node(i) if rhs else None)
         else:
             self._visit(lhs)
 

Cython/Compiler/TypeInference.py

@@ -61,8 +61,8 @@ class MarkParallelAssignments(EnvTransform):
                 parallel_node.assigned_nodes.append(lhs)
 
         elif isinstance(lhs, ExprNodes.SequenceNode):
-            for arg in lhs.args:
-                self.mark_assignment(arg, object_expr)
+            for i, arg in enumerate(lhs.args):
+                self.mark_assignment(arg, rhs.inferable_item_node(i))
         else:
             # Could use this info to infer cdef class attributes...
             pass

tests/run/arrayassign.pyx

 # mode: run
 
+cimport cython
+
 def test_literal_list():
     """
     >>> test_literal_list()
@@ -141,6 +143,8 @@ def test_ptr_literal_list_slice_end():
     a[:5] = [1,2,3,4,5]
     return (a[0], a[1], a[2], a[3], a[4])
 
+
+@cython.test_assert_path_exists('//ReturnStatNode//CoerceToPyTypeNode')
 def test_multiple_from_slice():
     """
     >>> test_multiple_from_slice()
@@ -150,6 +154,7 @@ def test_multiple_from_slice():
     x, y, z = a[1:4]
     return x, y, z
 
+
 def test_slice_from_multiple():
     """
     >>> test_slice_from_multiple()