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Estimated hours taken: 20 Branches: main When creating a new backtrackable reference that uses choicepoint ids to avoid redundant trailing, set the initial value of the id using MR_null_choicepoint_id() rather than MR_current_choicepoint_id(). If the current id is used, any updates that are performed before the next choicepoint is created will not be trailed since the code for updating the reference checks the stored id against the id that is current at the time of the update, and only adds a trail entry if they differ. Normally this wouldn't be a problem because if execution ever does backtrack to that initial choicepoint then it means it has backtracked to a point before the reference was created, hence the reference should no longer be live and it wouldn't matter that the reference was not untrailed back to its initial value. In this case the only effect of this change is that at most one unnecessary entry may be added to the trail. However, if a predicate that creates such a reference is tabled, then the reference will still exist in the table even after backtracking, and will be produced again if that predicate is later called. At this point the reference will not necessarily have its correct initial value. doc/reference_manual.texi: In the section on avoiding redundant trailing, advise users to use MR_null_choicepoint_id() if a mutable data structure is created by a predicate or function that is tabled. extras/references/reference.m: Use MR_null_choicepoint_id() in the implementation of new_reference/2, and document the reason. extras/references/tests/Mmakefile: extras/references/tests/glob_test_2.m: extras/references/tests/glob_test_2.exp: A test case that fails in grade asm_fast.gc.tr with the previous version of reference.m, but succeeds now.
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