handle modifications on lines with an error

when processing a document change, if only a single line is modified,
the line number of the line is checked to see if it has an error and if
it does, the error will be removed from the errors list if the cursor
is within the error or when the cursor and error is at the end of the
line, or the error column is adjusted if the modification occurs before
the error (no action is take if the cursor is after the error)

to support the adjusting of the error column, new functions were added
to the error list and error item classes

editbox.cpp

@@ -433,6 +433,36 @@ void EditBox::documentChanged(int position, int charsRemoved, int charsAdded)
 		}
 		m_lineCount = newLineCount;
 	}
+	else  // single line modified, reset error if line has an error
+	{
+		int errIndex = m_errors.findIndex(changeLine);
+		if (errIndex != -1)
+		{
+			int errCol = m_errors.at(errIndex).column();
+			int errLen = m_errors.at(errIndex).length();
+			int col = cursor.positionInBlock();
+			if (col - charsAdded <= errCol + errLen)
+			{
+				// cursor is within or before error
+				if (cursor.atBlockEnd() && col + charsRemoved >= errCol
+					|| col - charsAdded + charsRemoved > errCol)
+				{
+					// cursor and error at end of line or cursor is within error
+					// remove error
+					m_errors.resetChange();
+					m_errors.removeAt(errIndex);
+				}
+				else  // cursor is before error, update error
+				{
+					m_errors.resetChange();
+					m_errors.moveColumn(errIndex, charsAdded - charsRemoved);
+				}
+				updateErrors(m_errors);
+				// cause error message to be removed from status line
+				emit cursorChanged();
+			}
+		}
+	}
 	m_modifiedLine = m_modifiedLine == -2 ? -1 : cursor.blockNumber();
 }
 

errorlist.cpp

@@ -147,4 +147,12 @@ void ErrorList::setChangeIndex(int index, Operation operation)
 }
 
 
+// function to move the error due to inserted or deleted characters
+void ErrorList::moveColumn(int index, int chars)
+{
+	(*this)[index].moveColumn(chars);
+	setChangeIndex(index, Change_Operation);
+}
+
+
 // end: errorlist.cpp

errorlist.h

@@ -63,6 +63,10 @@ class ErrorItem
 	{
 		m_lineNumber--;
 	}
+	int moveColumn(int chars)
+	{
+		m_column += chars;
+	}
 	int column(void) const
 	{
 		return m_length >= 0 ? m_column : -m_length;
@@ -97,6 +101,7 @@ class ErrorList : public QList<ErrorItem>
 	void replace(int index, const ErrorItem &value);
 	void incrementLineNumber(int index);
 	void decrementLineNumber(int index);
+	void moveColumn(int index, int chars);
 
 	void resetChange(void)
 	{