Note that not all checks refer to the source code.
For these the result will be NULL.
failed_positions(gp)gp output.
A list of lists of positions. See details below.
For the ones that do, the results is a list, one for each failure.
Since the same check can fail multiple times. A single failure
is a list with entries: filename, line_number,
column_number, ranges. ranges is a list of
pairs of start and end positions for each line involved in the
check.