properly coerce Py_UCS4 characters to a unicode string when for-loop target requires it

Cython/Compiler/Optimize.py

@@ -348,15 +348,19 @@ class IterationTransform(Visitor.VisitorTransform):
                 is_temp = False,
                 ))
 
+        target_value = ExprNodes.PythonCapiCallNode(
+            slice_node.pos, "__Pyx_PyUnicode_READ",
+            self.PyUnicode_READ_func_type,
+            args = [kind_temp, data_temp, counter_temp],
+            is_temp = False,
+            )
+        if target_value.type != node.target.type:
+            target_value = target_value.coerce_to(node.target.type,
+                                                  self.current_scope)
         target_assign = Nodes.SingleAssignmentNode(
             pos = node.target.pos,
             lhs = node.target,
-            rhs = ExprNodes.PythonCapiCallNode(
-                slice_node.pos, "__Pyx_PyUnicode_READ",
-                self.PyUnicode_READ_func_type,
-                args = [kind_temp, data_temp, counter_temp],
-                is_temp = False,
-                ))
+            rhs = target_value)
         body = Nodes.StatListNode(
             node.pos,
             stats = [target_assign, node.body])

tests/run/cython3.pyx

@@ -81,6 +81,16 @@ def str_type_is_unicode():
     cdef str s = 'abc'
     return str, s
 
+def loop_over_unicode_literal():
+    """
+    >>> print( loop_over_unicode_literal() )
+    Py_UCS4
+    """
+    # Py_UCS4 can represent any Unicode character
+    for uchar in 'abcdefg':
+        pass
+    return cython.typeof(uchar)
+
 def list_comp():
     """
     >>> list_comp()

tests/run/py_ucs4_type.pyx

@@ -201,6 +201,17 @@ def count_lower_case_characters_slice_reversed(unicode ustring):
              count += 1
     return count
 
+def loop_object_over_unicode_literal():
+    """
+    >>> print(loop_object_over_unicode_literal())
+    abcdefg
+    """
+    cdef object uchar
+    chars = []
+    for uchar in u'abcdefg':
+        chars.append(uchar)
+    return u''.join(chars)
+
 @cython.test_assert_path_exists('//SwitchStatNode')
 @cython.test_fail_if_path_exists('//ForInStatNode')
 def iter_and_in():

tests/run/type_inference.pyx

@@ -341,6 +341,16 @@ def loop_over_unicode():
         pass
     return typeof(uchar)
 
+def loop_over_unicode_literal():
+    """
+    >>> print( loop_over_unicode_literal() )
+    Py_UCS4
+    """
+    # Py_UCS4 can represent any Unicode character
+    for uchar in u'abcdefg':
+        pass
+    return typeof(uchar)
+
 def loop_over_int_array():
     """
     >>> print( loop_over_int_array() )