New lint: unused_enumerate_value
#14443
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Ideally we should also check if the arbitrary type implements impl ExactSizeIterator, the trait isn't very well known. |
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Emm.. I doubt it because |
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In that case, we could just emit a warning if it's not coming from a ExactSizeIterator. I don't think we'll get much use if we limit the lint to just the trait. |
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Updated. Now arbitrary type is covered. |
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@blyxyas does this look good now? |
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| && let Some((DefKind::AssocFn, call_id)) = cx.typeck_results().type_dependent_def(arg.hir_id) | ||
| && cx.tcx.is_diagnostic_item(sym::enumerate_method, call_id) |
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Smart here to check for both Enumerate type and .enumerate(). This would avoid us linting on cases like iter.enumerate().map(), which could use iter in unforeseen ways.
| && let receiver_ty = cx.typeck_results().expr_ty(recv) | ||
| // TODO: Replace with `sym` when it's available | ||
| && let Some(exact_size_iter) = get_trait_def_id(cx.tcx, &paths::ITER_EXACT_SIZE_ITERATOR) | ||
| && implements_trait(cx, receiver_ty, exact_size_iter, &[]) |
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Leaving this as an open question for the FCP, but I still think that we should not only lint for types that implement iter_exact_size_iterator, as len() being an idiomatic standard is practically guaranteed. In fact, len() that does not report exact length as an usize would be considered a very bad practice.
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Checking for len is implemented in remove_trailing_iter because we should only remove the iter call if the iterator is created in this expr.
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Everything is looking great! I opened the FCP on Zulip |
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From the FCP I find it not that reasonable as I initial thought about this lint. I'll close this pr for now. |
for (i, _) in iter.enumerate()can be replaced withfor i in 0..iter.len()if the iterator implementsExactSizeIterator.Closes #14430
changelog: [
unused_enumerate_value]: new lint