From ccf857a3db566e41ba8167be6442441cdf92a9e3 Mon Sep 17 00:00:00 2001
From: apnadkarni <apnmbx-wits@yahoo.com>
Date: Sun, 16 Jul 2023 06:15:36 +0000
Subject: Bug [a366c6efee]

---
 generic/tclInt.h     |  4 ++--
 generic/tclListObj.c | 15 ++++++++++-----
 tests/lreplace.test  |  9 +++++++++
 3 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/generic/tclInt.h b/generic/tclInt.h
index ffceb5c..61ad487 100644
--- a/generic/tclInt.h
+++ b/generic/tclInt.h
@@ -2606,8 +2606,8 @@ typedef struct ListRep {
  * (1) No string representation exists which means it will obviously have
  * to be generated from the list representation when needed
  * (2) The ListStore flags is marked canonical. This is done at the time
- * the string representation is generated from the list IF the list
- * representation does not have a span (see comments in UpdateStringOfList).
+ * the string representation is generated from the list under certain
+ * conditions (see comments in UpdateStringOfList).
  * (3) The list representation does not have a span component. This is
  * because list Tcl_Obj's with spans are always created from existing lists
  * and never from strings (see SetListFromAny) and thus their string
diff --git a/generic/tclListObj.c b/generic/tclListObj.c
index 7a8f9ab..2f433c5 100644
--- a/generic/tclListObj.c
+++ b/generic/tclListObj.c
@@ -3448,16 +3448,21 @@ UpdateStringOfList(
      * Mark the list as being canonical; although it will now have a string
      * rep, it is one we derived through proper "canonical" quoting and so
      * it's known to be free from nasties relating to [concat] and [eval].
-     * However, we only do this if this is not a spanned list. Marking the
-     * storage canonical for a spanned list make ALL lists using the storage
-     * canonical which is not right. (Consider a list generated from a
+     * However, we only do this if 
+     * 
+     * (a) the store is not shared as a shared store may be referenced by
+     * multiple lists with different string reps. (see [a366c6efee]), AND
+     *
+     * (b) list does not have a span. Consider a list generated from a
      * string and then this function called for a spanned list generated
-     * from it). On the other hand, a spanned list is always canonical
+     * from the original list. We cannot mark the list store as canonical as
+     * that would also make the originating list canonical, which it may not
+     * be. On the other hand, the spanned list itself is always canonical
      * (never generated from a string) so it does not have to be explicitly
      * marked as such. The ListObjIsCanonical macro takes this into account.
      * See the comments there.
      */
-    if (listRep.spanPtr == NULL) {
+    if (listRep.storePtr->refCount < 2 && listRep.spanPtr == NULL) {
 	LIST_ASSERT(listRep.storePtr->firstUsed == 0);/* Invariant */
 	listRep.storePtr->flags |= LISTSTORE_CANONICAL;
     }
diff --git a/tests/lreplace.test b/tests/lreplace.test
index 009170e..55b3ee3 100644
--- a/tests/lreplace.test
+++ b/tests/lreplace.test
@@ -505,6 +505,15 @@ test ledit-5.2 {compiled lreplace: Bug 47ac84309b} {
     }} {a b c}
 } {a b A c}
 
+test ledit-bug-a366c6efee {Bug [a366c6efee]} -body {
+    apply {{} {
+        set l { }
+        string length [ledit l 1 1]; # Force string generation
+        set result foo
+        append result " " bar
+    }}
+} -result "foo bar"
+
 # Testing for compiled behaviour. Far too many variations to check with
 # spelt-out tests. Note that this *just* checks whether the compiled version
 # and the interpreted version are the same, not whether the interpreted
-- 
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