Allow assessment bonus points to account for question score beyond 100%

[jonatanschroeder]

The implementation of assessment bonus points in #4090 was intended to allow some questions to effectively act as "bonus questions", by allowing the assessment score to go above 100% based on question completion (rather than credit for early work, which was already an option). This implementation allows the setting of maxBonusPoints, which allowed the sum of all question points to add up to more than the assessment's maxPoints, and thus the score to more than 100%.

This implementation, though, limited maxPoints+maxBonusPoints to the total points assigned to the questions in the assessment. This assumes that questions are limited to a score of 100%, which is true in most auto-graded contexts, but can be overridden in manual grading questions. A manual grading can provide points that go above the limit of the question. In fact, the rubric settings even have an explicit option to override the maximum number of points in the question.

The example proposed by @firasm was an assessment with a single question that had 20 auto points and 80 manual points, with a rubric on manual points that allowed a question to get up to 82 points. The meant that the question could go up to 102 (out of 100) points. However, since the question is assigned 100 points, this would limit the assessment score to 100. Setting maxBonusPoints to 2, with maxPoints at 100, would be overridden by the assessment instance update sproc to set maxBonusPoints to zero, so the setting would be moot.

The proposal in this issue (as discussed on Slack) is that this limit on maxBonusPoints be removed, allowing the assessment to honour the bonus points assigned in manual grading in the assessment score. This would only affect assessments that set both maxPoints and maxBonusPoints to a specific value, since setting maxBonusPoints without maxPoints has a well-defined behaviour that should remain for backwards compatibility. In essence, this would mean removing the LEAST restriction in this line:

PrairieLearn/apps/prairielearn/src/sprocs/assessment_instances_update.sql

Line 108 in 0fb66e2

assessment_max_bonus_points := GREATEST(LEAST(assessment_max_bonus_points, zones_total_max_points - new_assessment_instance_max_points), 0);

plus updates in documentation.