Fix UC Requirements disappearing on plans with fewer than 3 Fall/Spring terms - #1214
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…ring terms The Senior Residence block picked the 3rd-from-last Fall/Spring column as the divider via get_element with a negative index, which yields an undefined Column. findIndex then called get_attr on it and threw, taking the whole UC Requirements group down with it (and, before #1173, the entire panel). There was no way to guard this in BtLL because if_else evaluated both branches. Make if_else and elseifs evaluate only the taken branch, then move the divider lookup into a helper that the UC program only calls when there are at least 3 Fall/Spring terms; otherwise the whole plan is senior year. Add BtLL tests for branch laziness and for the UC program on a two-semester plan.
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Before #1173 this threw and made all course requirements vanish. After #1173, only the UC Requirements group vanished. The root cause is an indexing error, since we get the columns with
get_element(only_spring_fall, length - 3), which breaks when the course plan only has 1-2 semesters. However this is in an if/else block that shouldn't be evaluated with 1-2 course semesters.The root cause is that BtLL evaluates both blocks in if/else statements, rather than lazily like every other language. We need to evaluate only the block that will run to make get_element for this application safe.
Added unit tests that verify that we don't evaluate something that would throw in if/else and elseif blocks. Also added a BtLL test that runs
UC_REQ_BTLLagainst a two-semester plan; fails onmain, passes here.The frontend evaluates
PlanRequirement.codefrom Mongo, so the UC doc needs to be re-seeded (npm run seed:requirementsinpackages/BtLL) for this to take effect.