[PATCH] Fix "bad text index 4" error

[PATCH] Fix "bad text index 4" error

[Keith Seitz]

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Hi,

After seeing this bug reported for /ages/, I think I finally developed a 
reproducible test case or at least one of them.

I can reproduce this error by changing a previously executable line (at 
which insight had a saved breakpoint) to a comment and recompiling. Now 
the line was no longer executable, but we had a breakpoint in the 
session that said that it was. That combined with a bogus text index 
("4" is not a valid text widget index) caused the infamous "bad text 
index '4'" error.

The solution is to search for the next nearest executable line, and use 
that line number for subsequent deductions/operations/indices. This 
appears to work on the test case that I developed.

Insight inserts the breakpoint at the next executable line it finds, and 
when gdb actually breaks at the breakpoint, it and insight are in sync 
as to where we stopped.

My hope is that this is the last of this accursed bug that I'll see, but 
if you do see it again, and you can reproduce it, PLEASE let me know.

Keith

ChangeLog
2009-10-08  Keith Seitz  <keiths@redhat.com>

	* library/srctextwin.ith (ExecutableLineLimit): Define.
	* library/srctextwin.itb (insertBreakTag): Search for next
	executable line, just in case they changed.
	When there are no tags on a line, the proper index is
	line.4, not just 4.

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Index: library/srctextwin.ith
===================================================================
RCS file: /cvs/src/src/gdb/gdbtk/library/srctextwin.ith,v
retrieving revision 1.14
diff -u -p -r1.14 srctextwin.ith
--- library/srctextwin.ith	23 Dec 2005 18:26:50 -0000	1.14
+++ library/srctextwin.ith	9 Oct 2009 02:51:11 -0000
@@ -1,5 +1,5 @@
 # SrcTextWin class definition, for Insight
-# Copyright (C) 1997, 1998, 1999, 2001 Red Hat, Inc.
+# Copyright (C) 1997, 1998, 1999, 2001, 2009 Red Hat, Inc.
 #
 # This program is free software; you can redistribute it and/or modify it
 # under the terms of the GNU General Public License (GPL) as published by
@@ -160,4 +160,8 @@ itcl::class SrcTextWin {
 
   protected common TimeOut 100 ;# The timeout value for variable balloon help
 
+  # Executabe line search limit: When an executable changes, we might
+  # have a breakpoint at a location that is no longer valid.  This variable
+  # limits the search for the "nearest" (next) executable line.
+  protected common ExecutableLineLimit 100
 }
Index: library/srctextwin.itb
===================================================================
RCS file: /cvs/src/src/gdb/gdbtk/library/srctextwin.itb,v
retrieving revision 1.44
diff -u -p -r1.44 srctextwin.itb
--- library/srctextwin.itb	16 Dec 2008 09:07:57 -0000	1.44
+++ library/srctextwin.itb	9 Oct 2009 02:51:11 -0000
@@ -1,5 +1,5 @@
 # Paned text widget for source code, for Insight
-# Copyright (C) 1997, 1998, 1999, 2001, 2002, 2008 Red Hat, Inc.
+# Copyright (C) 1997, 1998, 1999, 2001, 2002, 2008, 2009 Red Hat, Inc.
 #
 # This program is free software; you can redistribute it and/or modify it
 # under the terms of the GNU General Public License (GPL) as published by
@@ -1362,6 +1362,14 @@ itcl::body SrcTextWin::insertBreakTag {w
   # tag.  We will query the length of the previous tag, so we don't have
   # to hard code it here.
   
+  # Find the nearest executable line
+  for {set i 0} {$i < $ExecutableLineLimit} {incr i} {
+    if {[line_is_executable $win [expr {$linenum + $i}]]} {
+      incr linenum $i
+      break
+    }
+  }
+
   set tag_list [$win tag names $linenum.0]
   set img_name [string range $tag 0 [expr [string length $tag] - 5]]
   
@@ -1378,7 +1386,7 @@ itcl::body SrcTextWin::insertBreakTag {w
     set other_tag [lindex $tag_list \
 		     [lsearch -glob $tag_list {*[bt]p_tag}]]
     if {$other_tag == ""} {
-      set stop 4
+      set stop "$linenum.4"
     } else {
       set stop [lindex [$win tag nextrange $other_tag \
 			  $linenum.0 "$linenum.0 lineend"] 1]