* generic/tclObj.c (TclContinuationsEnter): [Bug 2895323]: Updated

	comments to describe when the function can be entered for the same
	Tcl_Obj* multiple times. This is a continuation of the 2009-11-10
	entry where a memory leak was plugged, but where not sure if that
	was just a band-aid to paper over some other error. It isn't, this
	is a legal situation.

2 files changed, 28 insertions, 5 deletions

diff --git a/ChangeLog b/ChangeLog
index 894fbd4..2c1bd26 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,12 @@
+2009-12-10  Andreas Kupries  <andreask@activestate.com>
+
+	* generic/tclObj.c (TclContinuationsEnter): [Bug 2895323]: Updated
+	comments to describe when the function can be entered for the same
+	Tcl_Obj* multiple times. This is a continuation of the 2009-11-10
+	entry where a memory leak was plugged, but where not sure if that
+	was just a band-aid to paper over some other error. It isn't, this
+	is a legal situation.
+
 2009-12-10  Miguel Sofer  <msofer@users.sf.net>
 
 	* generic/tclBasic.c:   Reducing the # of moving parts for
diff --git a/generic/tclObj.c b/generic/tclObj.c
index 5913dd1..667fd90 100644
--- a/generic/tclObj.c
+++ b/generic/tclObj.c
@@ -13,7 +13,7 @@
  * See the file "license.terms" for information on usage and redistribution of
  * this file, and for a DISCLAIMER OF ALL WARRANTIES.
  *
- * RCS: @(#) $Id: tclObj.c,v 1.164 2009/11/10 17:57:39 andreas_kupries Exp $
+ * RCS: @(#) $Id: tclObj.c,v 1.165 2009/12/10 19:13:26 andreas_kupries Exp $
  */
 
 #include "tclInt.h"
@@ -584,10 +584,24 @@ TclContinuationsEnter(Tcl_Obj* objPtr,
 
     if (!newEntry) {
 	/*
-	 * Somehow we're entering ContLineLoc data for the same value (objPtr)
-	 * more than one time.  Not sure whether that's expected, or a sign of
-	 * trouble, but at a minimum, we should take care not to leak the old
-	 * entry.
+	 * We're entering ContLineLoc data for the same value more than one
+	 * time. Taking care not to leak the old entry.
+	 *
+	 * This can happen when literals in a proc body are shared. See for
+	 * example test info-30.19 where the action (code) for all branches of
+	 * the switch command is identical, mapping them all to the same
+	 * literal. An interesting result of this is that the number and
+	 * locations (offset) of invisible continuation lines in the literal
+	 * are the same for all occurences.
+	 *
+	 * Note that while reusing the existing entry is possible it requires
+	 * the same actions as for a new entry because we have to copy the
+	 * incoming num/loc data even so. Because we are called from
+	 * TclContinuationsEnterDerived for this case, which modified the
+	 * stored locations (Rebased to the proper relative offset). Just
+	 * returning the stored entry would rebase them a second time, or
+	 * more, hosing the data. It is easier to simply replace, as we are
+	 * doing.
 	 */
 
 	ckfree((char *) Tcl_GetHashValue(hPtr));