Short story: it was a source of bugs, there was only one handcrafted message over 650, and, to quote François Pottier, "you seem to have misunderstood what the various commands do". Long story: the proper steps to update the error messages after modifying the parser are 1. update the old states with --update-errors 2. generate the new states with --list-errors 3. compare the old and new states with --compare-errors 4. manually reconcile the differences between the old and new states 5. write error messages for the new states 6. add %on_error_reduce and go back to step 1, if step 5 is too hard 7. check that the error messages for the old states are still meaningful 8. check that the set of states is both correct (--compile-errors) and complete (--compare-errors) We were doing only step 1 and half of step 8. Doing the other half of step 8 would have prevented issue #172 from occurring. But that would have meant doing step 4 after each parser modification, which was never done. Note that step 2 is so expensive that it is impossible to perform step 8 during continuous integration. Given the work needed to update the error messages after a syntax change, I don't think we can reliably use them until WhyML no longer evolves.
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