On Wed, Jul 04, 2018 at 11:53:15AM -0400, David T. Lewis wrote:
> On Wed, Jul 04, 2018 at 02:35:59PM +0200, karl ramberg wrote:
> > 
> > On Wed, Jul 4, 2018 at 11:10 AM K K Subbu <kksubbu.ml at gmail.com> wrote:
> > 
> > > On Tuesday 03 July 2018 04:40 AM, Tim Johnson wrote:
> > > > 1. File-in the .cs as attached*.
> > > > 2. In a system browser, click on the class, then click on the [?] button
> > > > to view class comment.
> > > > 3. Notice the styled text in the comment.
> > > > 4. Click around the comment pane a bit.
> > > > 5. Eventually, see "Error: subscript is out of bounds: 71" appear over
> > > > and over until you interrupt.
> > > In step 4, it is sufficient to click once near the bottom of the pane
> > > when the cursor changes from I-bar to arrow and then wait. This will
> > > trigger the error, but the error window triggers itself recursively
> > > around 50 times before stopping and displaying the windows.
> > >
> > > I added an assert to catch it before recursion:
> > >
> > >     self assert: lastIndex < sourceString size.
> > >
> > > The assert window itself throws up another error, but that is a topic
> > > for another thread ;-).
> > >
> > > Regards .. Subbu
> 
> > 
> > Hi,
> > See class comment i NewParagraph for a hint of what happens.
> > A empty lineSpan 71 to: 70 is added to the end of the paragraph, when you
> > double click below the text.
> > When the character scanner looks for characters outside of the string at
> > index 71 it cause a recursion.
> > 
> > Best,
> > Karl
> > 
> 
> Good tiip to look at the NewParagraph class comment, there is apparently
> some left over messiness in here somewhere.
> 
> Another way to trigger the bug using the test case with FooClient is
> to position the cursor in the comment pane and use keyboard right cursor
> to move to the end of the comment. This causes the same bounds error but
> takes a different path through the code leading to the error.
> 
> Looking through the stack in a debugger after triggering the error with
> the mouse, here are a few notes (but no conclusions):
> 
> On mouseUp: we enter Editor>>selectWord then call Editor>>selectWordLeftDelimiters:rightDelimiters:
> which has this:
> 
> 	"Select the whole text when clicking before first or after last character"
> 	(here > string size or: [here < 2]) ifTrue: [^self selectFrom: 1 to: string size].
> 
> where string is the 70 character String derived from the Text.
> 
> At this point we are trying to select from 1 to 70 (the whole string for
> the entire text) in TextEditor>>selectFrom:to:
> 
> This calls Editor>>selectInvisiblyFrom:to: and here the stop index is
> set past the size of the string:
> 
>   selectInvisiblyFrom: start to: stop
>      "Select the designated characters, inclusive.  Make no visual changes."
> 
>      self markIndex: start pointIndex: stop + 1
> 
> From this point we are trying to go from index 1 to index 71 over a string
> of size 70, and eventually end up with the out of bounds exception.
> 
> A clue that this might be accumulation of kludges: Looking at senders of
> selectInvisiblyFrom:to: (such as TextEditor>>addText:event:) shows a number
> of methods that subtract 1 from the stop index when before calling the method
> that adds 1 back to the stop index. This certainly does not have a good smell.
> 
> It is not clear to me why selectInvisiblyFrom:to: would be adding one to the
> stop index, but I see that the method stamp is jmv 5/27/2011, which suggests
> to me that we should take a look at Cuis to figure out how this is intended
> to function. Cuis does not show any cases of senders of selectInvisiblyFrom:to:
> that subtract 1 from the stop index, and the Cuis implementation of
> selectInvisiblyFrom:to: is that same as Squeak.
> 
> Dave
> 

One more note: This is an old bug. It is present in Squeak 4.1 but not in
Squeak 3.9 so whatever the cause, it has been with us for a while.

Dave