join UnicodeNode sequences in JoinedStrNode at compile time

Cython/Compiler/ParseTreeTransforms.py

@@ -7,6 +7,7 @@ cython.declare(PyrexTypes=object, Naming=object, ExprNodes=object, Nodes=object,
                error=object, warning=object, copy=object, _unicode=object)
 
 import copy
+import itertools
 
 from . import PyrexTypes
 from . import Naming
@@ -350,15 +351,24 @@ class PostParse(ScopeTrackingTransform):
 
     def visit_JoinedStrNode(self, node):
         """
-        Clean up after the parser by discarding empty Unicode strings.
-        Empty or single-value join lists are not uncommon because f-string
-        format specs are always parsed into JoinedStrNodes.
+        Clean up after the parser by discarding empty Unicode strings and merging
+        substring sequences.  Empty or single-value join lists are not uncommon
+        because f-string format specs are always parsed into JoinedStrNodes.
         """
+        self.visitchildren(node)
+        unicode_node = ExprNodes.UnicodeNode
         values = []
-        for value in node.values:
-            if isinstance(value, ExprNodes.UnicodeNode) and not value.value:
-                continue  # ignore empty Unicode strings
-            values.append(value)
+        for is_unode_group, substrings in itertools.groupby(node.values, lambda v: isinstance(v, unicode_node)):
+            if is_unode_group:
+                substrings = list(substrings)
+                unode = substrings[0]
+                if len(substrings) > 1:
+                    unode.value = EncodedString(u''.join(node.value for node in substrings))
+                # ignore empty Unicode strings
+                if unode.value:
+                    values.append(unode)
+            else:
+                values.extend(substrings)
 
         if not values:
             node = ExprNodes.UnicodeNode(node.pos, value=EncodedString(''))
@@ -366,7 +376,6 @@ class PostParse(ScopeTrackingTransform):
             node = values[0]
         else:
             node.values = values
-        self.visitchildren(node)
         return node