match exhaustiveness diagnostics: show a trailing comma on singleton tuple consructors in witness patterns (and clean up a little) #145234
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By construction, `subpatterns` contains all fields in order. Witness patterns are constructed with all fields in order by `WitnessPat::wild_from_ctor` and `WitnessStack::apply_constructor`, and the order is preserved at `write_struct_like`'s call-site in `print_witness_pat`. It's thus no longer necessary to go looking for fields or handle missing fields.
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Some changes occurred in exhaustiveness checking cc @Nadrieril |
dianne
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Aug 10, 2025
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I haven't added a test specifically for singleton tuple witnesses since this test included them. I could add a separate test if it would be preferable, though, to make sure it's still tested even if this test changes.
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Constructor patterns of type
(T,)are written(pat,), not(pat). However, exhaustiveness/usefulness diagnostics would print them as(pat)when e.g. providing a witness of non-exhaustiveness and suggesting adding arms to make matches exhaustive; this would result in an error when applied.rust-analyzer already prints the trailing comma, so it doesn't need changing.
This also includes some cleanup in the second commit, with justification in the commit message.