From aefe754799655f3fa04cc84f4ea5d110d0289c46 Mon Sep 17 00:00:00 2001
From: dgp <dgp@users.sourceforge.net>
Date: Wed, 15 May 2019 17:30:35 +0000
Subject: Tests and fix for [scale ... -variable].

---
 generic/tkScale.c | 23 ++++++++++++++++++++++-
 tests/scale.test  | 26 ++++++++++++++++++++++++++
 2 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/generic/tkScale.c b/generic/tkScale.c
index ef67630..3920aea 100644
--- a/generic/tkScale.c
+++ b/generic/tkScale.c
@@ -1198,7 +1198,28 @@ ScaleVarProc(
      */
 
     if (flags & TCL_TRACE_UNSETS) {
-	if ((flags & TCL_TRACE_DESTROYED) && !(flags & TCL_INTERP_DESTROYED)) {
+
+        if (!Tcl_InterpDeleted(interp) && scalePtr->varNamePtr) {
+            ClientData probe = NULL;
+
+            do {
+                probe = Tcl_VarTraceInfo(interp,
+                        Tcl_GetString(scalePtr->varNamePtr),
+                        TCL_GLOBAL_ONLY|TCL_TRACE_WRITES|TCL_TRACE_UNSETS,
+                        ScaleVarProc, probe);
+                if (probe == (ClientData)scalePtr) {
+                    break;
+                }
+            } while (probe);
+            if (probe) {
+                /* 
+                 * We were able to fetch the unset trace for our
+                 * varNamePtr, which means it is not unset and not
+                 * the cause of this unset trace. Instead some outdated
+                 * former variable must be, and we should ignore it.
+                 */
+                return NULL;
+            }
 	    Tcl_TraceVar2(interp, Tcl_GetString(scalePtr->varNamePtr),
 		    NULL, TCL_GLOBAL_ONLY|TCL_TRACE_WRITES|TCL_TRACE_UNSETS,
 		    ScaleVarProc, clientData);
diff --git a/tests/scale.test b/tests/scale.test
index 79524eb..ba70285 100644
--- a/tests/scale.test
+++ b/tests/scale.test
@@ -1524,6 +1524,32 @@ test scale-21.2 {Bug [55b95f578a] again - Bignum value for -from/-to with scale
     destroy .s
 } -result {}
 
+test scale-22.1 {Bug [5d991b822e]} {
+    # Want this not to crash
+    set var INIT
+    scale .b -variable var
+    trace add variable var unset {apply {args {
+        .b configure -variable {}
+    }}}
+    pack .b
+    bind .b <Configure> {unset var}
+    update
+    destroy .b
+} {}
+test scale-22.2 {Bug [5d991b822e]} {
+    # Want this not to leak traces
+    set var INIT
+    scale .b -variable var
+    trace add variable var unset {apply {args {
+        .b configure -variable new
+    }}}
+    pack .b
+    bind .b <Configure> {unset -nocomplain var}
+    update
+    destroy .b
+    unset new
+} {}
+
 option clear
 
 # cleanup
-- 
cgit v0.12