Another Undo/Redo Problem

Now that the program model is keeping a list of errors in the program, the next incremental change is to report changes to this list to the edit box so that the errors can be highlighted.  While testing these changes, another problem was found with the detection of lines changes when using redo.

The problem occurs when the current line is modified (specifically from a redo) and another redo causes a change to occur in another part of the program.  The line that was modified does not get reported.  This can also occur with an undo, but only when going up and down through the undo/redo stack.  The line is not being reported because for undo and redo, the document change signal occurs before the cursor moved signal (where a modified line gets reported).

A check was added towards the beginning of the document change slot after gathering information about the change but before acting upon it.  If there is a modified line and the modified line is not at the line of the change, then the modified line is captured before processing the current change.

A complication occurs when the modified line is after the line of the change.  When reporting the modified line, the capture routine needs to report the line number contained in the modified line variable, however, when retrieving the text of this line, since the document has already been modified by the undo or redo, the number of the line is not necessarily the same if the undo or redo inserted or deleted lines.

Fortunately, the offset of where the actual program line is (after the undo or redo change) is the same as the net line count change caused by the undo or redo.  The capture modified line routine was modified to take an optional offset.  The net line count change is passed if the modified line is after the line of the change, otherwise, no offset is needed if the modified line is before the change.

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