Fix constant folding of multiplied string literals when they appear in another...

Fix constant folding of multiplied string literals when they appear in another constant expression. In this case, the multiplied value was lost and replaced by the original value.

CHANGES.rst

@@ -2,6 +2,16 @@
 Cython Changelog
 ================
 
+0.28.6 (??)
+===================
+
+Bugs fixed
+----------
+
+* Multiplied string literals lost their factor when they are part of another
+  constant expression (e.g. 'x' * 10 + 'y' => 'xy').
+
+
 0.28.5 (2018-08-03)
 ===================
 

Cython/Compiler/Optimize.py

@@ -4234,7 +4234,7 @@ class ConstantFolding(Visitor.VisitorTransform, SkipDeclarations):
                     string_node.bytes_value.encoding)
         else:
             assert False, "unknown string node type: %s" % type(string_node)
-        string_node.value = build_string(
+        string_node.constant_result = string_node.value = build_string(
             string_node.value * multiplier,
             string_node.value.encoding)
         return string_node

tests/run/unicodeliterals.pyx

@@ -85,6 +85,8 @@ __doc__ = br"""
     True
     >>> wide_literal == u'\\U00101234'   # unescaped by Python
     True
+    >>> ustring_in_constant_tuple == ('a', u'abc', u'\\N{SNOWMAN}', u'x' * 3, u'\\N{SNOWMAN}' * 4 + u'O')  or  ustring_in_constant_tuple  # unescaped by Python
+    True
 """
 
 if sys.version_info >= (2,6,5):
@@ -118,3 +120,5 @@ add = u'Søk ik' + u'üÖä' + u'abc'
 null = u'\x00'
 
 wide_literal = u'\U00101234'
+
+ustring_in_constant_tuple = ('a', u'abc', u'\N{SNOWMAN}', u'x' * 3, u'\N{SNOWMAN}' * 4 + u'O')