Fix bug in delimited_list (premature streamline), issue #408

2 files changed, 30 insertions, 2 deletions

diff --git a/pyparsing/__init__.py b/pyparsing/__init__.py
index ffe89d0..e502ba3 100644
--- a/pyparsing/__init__.py
+++ b/pyparsing/__init__.py
@@ -121,7 +121,7 @@ class version_info(NamedTuple):
 
 
 __version_info__ = version_info(3, 0, 10, "final", 0)
-__version_time__ = "05 Jul 2022 01:03 UTC"
+__version_time__ = "09 Jul 2022 13:41 UTC"
 __version__ = __version_info__.__version__
 __versionTime__ = __version_time__
 __author__ = "Paul McGuire <ptmcg.gm+pyparsing@gmail.com>"
diff --git a/pyparsing/helpers.py b/pyparsing/helpers.py
index 802389c..ecb382b 100644
--- a/pyparsing/helpers.py
+++ b/pyparsing/helpers.py
@@ -1,6 +1,7 @@
 # helpers.py
 import html.entities
 import re
+import sys
 import typing
 
 from . import __diag__
@@ -46,7 +47,34 @@ def delimited_list(
         expr = ParserElement._literalStringClass(expr)
     expr = typing.cast(ParserElement, expr)
 
-    expr_copy = expr.copy().streamline()
+    def make_deep_name_copy(expr):
+        from collections import deque
+        MAX_EXPRS = sys.getrecursionlimit()
+        seen = set()
+        to_visit = deque([(None, expr)])
+        cpy = None
+        num_exprs = 0
+        while to_visit and num_exprs < MAX_EXPRS:
+            parent, cur = to_visit.pop()
+            num_exprs += 1
+            if cur in seen:
+                continue
+            seen.add(cur)
+            cur = cur.copy()
+            if parent is None:
+                cpy = cur
+            else:
+                if hasattr(parent, "expr"):
+                    parent.expr = cur
+                elif hasattr(parent, "exprs"):
+                    parent.exprs.append(cur)
+
+            to_visit.extend((cur, sub) for sub in cur.recurse()[::-1])
+            getattr(cur, "exprs", []).clear()
+
+        return cpy
+
+    expr_copy = make_deep_name_copy(expr).streamline()
     dlName = f"{expr_copy} [{delim} {expr_copy}]...{f' [{delim}]' if allow_trailing_delim else ''}"
 
     if not combine: