From 45b7c8a7643c1ccb4268653e962709300c237d85 Mon Sep 17 00:00:00 2001
From: dgp <dgp@users.sourceforge.net>
Date: Mon, 26 Jun 2017 19:17:12 +0000
Subject: Try to make good stack trace. Fallback to making not-so-good stack
 trace. Stop failing altogether. Test in test suite, not program fragility.

---
 library/init.tcl | 50 ++++++++++++++++++++++++++++----------------------
 tests/init.test  |  2 +-
 2 files changed, 29 insertions(+), 23 deletions(-)

diff --git a/library/init.tcl b/library/init.tcl
index a202054..6173b86 100644
--- a/library/init.tcl
+++ b/library/init.tcl
@@ -284,14 +284,9 @@ proc unknown args {
 		    }
 		    append cinfo ...
 		}
-		append cinfo "\"\n    (\"uplevel\" body line 1)"
-		append cinfo "\n    invoked from within"
-		append cinfo "\n\"uplevel 1 \$args\""
-		#
-		# Try each possible form of the stack trace
-		# and trim the extra contribution from the matching case
-		#
-		set expect "$msg\n    while executing\n\"$cinfo"
+		set tail "\n    (\"uplevel\" body line 1)\n    invoked\
+			from within\n\"uplevel 1 \$args\""
+		set expect "$msg\n    while executing\n\"$cinfo\"$tail"
 		if {$errInfo eq $expect} {
 		    #
 		    # The stack has only the eval from the expanded command
@@ -305,21 +300,32 @@ proc unknown args {
 		# Stack trace is nested, trim off just the contribution
 		# from the extra "eval" of $args due to the "catch" above.
 		#
-		set expect "\n    invoked from within\n\"$cinfo"
-		set exlen [string length $expect]
-		set eilen [string length $errInfo]
-		set i [expr {$eilen - $exlen - 1}]
-		set einfo [string range $errInfo 0 $i]
-		#
-		# For now verify that $errInfo consists of what we are about
-		# to return plus what we expected to trim off.
-		#
-		if {$errInfo ne "$einfo$expect"} {
-		    error "Tcl bug: unexpected stack trace in \"unknown\"" {} \
-			[list CORE UNKNOWN BADTRACE $einfo $expect $errInfo]
+		set last [string last $tail $errInfo]
+		if {$last + [string length $tail] != [string length $errInfo]} {
+		    # Very likely cannot happen
+		    return -options $opts $msg
 		}
-		return -code error -errorcode $errCode \
-			-errorinfo $einfo $msg
+		set errInfo [string range $errInfo 0 $last-1]
+		set tail "\"$cinfo\""
+		set last [string last $tail $errInfo]
+		if {$last + [string length $tail] != [string length $errInfo]} {
+		    return -code error -errorcode $errCode \
+			    -errorinfo $errInfo $msg
+		}
+		set errInfo [string range $errInfo 0 $last-1]
+		set tail "\n    invoked from within\n"
+		set last [string last $tail $errInfo]
+		if {$last + [string length $tail] == [string length $errInfo]} {
+		    return -code error -errorcode $errCode \
+			    -errorinfo [string range $errInfo 0 $last-1] $msg
+		}
+		set tail "\n    while executing\n"
+		set last [string last $tail $errInfo]
+		if {$last + [string length $tail] == [string length $errInfo]} {
+		    return -code error -errorcode $errCode \
+			    -errorinfo [string range $errInfo 0 $last-1] $msg
+		}
+		return -options $opts $msg
 	    } else {
 		dict incr opts -level
 		return -options $opts $msg
diff --git a/tests/init.test b/tests/init.test
index 3a5197a..639389f 100644
--- a/tests/init.test
+++ b/tests/init.test
@@ -176,7 +176,7 @@ test init-4.$count {[Bug 46f801ed5a]} -setup {
 } -cleanup {
     array unset auto_index demo
     rename demo {}
-} -match glob -result *
+} -returnCodes error -result foo
 
 test init-5.0 {return options passed through ::unknown} -setup {
     catch {rename xxx {}}
-- 
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