Missing Debug Implementations

[seanmonstar]

The missing_debug_implementations will detect any public type that does not implement Debug. Usually all public types should implement Debug, even if it doesn't share all the internals in its formatting. This allows users to derive(Debug) on their types when they contain a type from std.

I ran the lint against crates that have types exported in std, and I've grouped the results below. I think the eventual goal should be to add #![deny(missing_debug_implementations)] to each crate. Any exceptions should be tagged #[allow(missing_debug_implementations)], though hopefully those should be very few.

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collections

• src/libcollections/binary_heap.rs:672 pub struct Iter<'a, T: 'a>
• src/libcollections/binary_heap.rs:712 pub struct IntoIter<T>
• src/libcollections/binary_heap.rs:744 pub struct Drain<'a, T: 'a>
• src/libcollections/btree/map.rs:188 pub struct Iter<'a, K: 'a, V: 'a>
• src/libcollections/btree/map.rs:195 pub struct IterMut<'a, K: 'a, V: 'a>
• src/libcollections/btree/map.rs:202 pub struct IntoIter<K, V>
• src/libcollections/btree/map.rs:210 pub struct Keys<'a, K: 'a, V: 'a>
• src/libcollections/btree/map.rs:216 pub struct Values<'a, K: 'a, V: 'a>
• src/libcollections/btree/map.rs:221 pub struct Range<'a, K: 'a, V: 'a>
• src/libcollections/btree/map.rs:227 pub struct RangeMut<'a, K: 'a, V: 'a>
• src/libcollections/btree/map.rs:237 pub enum Entry<'a, K: 'a, V: 'a>
• src/libcollections/btree/map.rs:253 pub struct VacantEntry<'a, K: 'a, V: 'a>
• src/libcollections/btree/map.rs:264 pub struct OccupiedEntry<'a, K: 'a, V: 'a>
• src/libcollections/btree/set.rs:49 pub struct Iter<'a, T: 'a>
• src/libcollections/btree/set.rs:55 pub struct IntoIter<T>
• src/libcollections/btree/set.rs:60 pub struct Range<'a, T: 'a>
• src/libcollections/btree/set.rs:66 pub struct Difference<'a, T: 'a>
• src/libcollections/btree/set.rs:73 pub struct SymmetricDifference<'a, T: 'a>
• src/libcollections/btree/set.rs:80 pub struct Intersection<'a, T: 'a>
• src/libcollections/btree/set.rs:87 pub struct Union<'a, T: 'a>
• src/libcollections/enum_set.rs:218 pub struct Iter<E>
• src/libcollections/linked_list.rs:59 pub struct Iter<'a, T: 'a>
• src/libcollections/linked_list.rs:79 pub struct IterMut<'a, T: 'a>
• src/libcollections/linked_list.rs:89 pub struct IntoIter<T>
• src/libcollections/linked_list.rs:1052 pub struct FrontPlace<'a, T: 'a>
• src/libcollections/linked_list.rs:1096 pub struct BackPlace<'a, T: 'a>
• src/libcollections/str.rs:120 pub struct Utf16Units<'a>
• src/libcollections/string.rs:1852 pub struct Drain<'a>
• src/libcollections/vec.rs:1551 pub struct IntoIter<T>
• src/libcollections/vec.rs:1649 pub struct Drain<'a, T: 'a>
• src/libcollections/vec_deque.rs:1739 pub struct Iter<'a, T: 'a>
• src/libcollections/vec_deque.rs:1795 pub struct IterMut<'a, T: 'a>
• src/libcollections/vec_deque.rs:1848 pub struct IntoIter<T>
• src/libcollections/vec_deque.rs:1881 pub struct Drain<'a, T: 'a>

rand

• src/librand/distributions/range.rs:32 pub struct Range<X>
• src/librand/distributions/gamma.rs:42 pub struct Gamma
• src/librand/distributions/gamma.rs:180 pub struct ChiSquared
• src/librand/distributions/gamma.rs:228 pub struct FisherF
• src/librand/distributions/gamma.rs:263 pub struct StudentT
• src/librand/distributions/normal.rs:32 pub struct StandardNormal(pub f64);
• src/librand/distributions/normal.rs:80 pub struct Normal
• src/librand/distributions/normal.rs:118 pub struct LogNormal
• src/librand/distributions/exponential.rs:33 pub struct Exp1(pub f64);
• src/librand/distributions/exponential.rs:62 pub struct Exp
• src/librand/distributions/mod.rs:57 pub struct RandSample<Sup>
• src/librand/distributions/mod.rs:80 pub struct Weighted<T>
• src/librand/distributions/mod.rs:96 pub struct WeightedChoice<'a, T: 'a>
• src/librand/isaac.rs:38 pub struct IsaacRng
• src/librand/isaac.rs:316 pub struct Isaac64Rng
• src/librand/chacha.rs:29 pub struct ChaChaRng
• src/librand/reseeding.rs:22 pub struct ReseedingRng<R, Rsdr>
• src/librand/reseeding.rs:107 pub struct ReseedWithDefault;
• src/librand/lib.rs:282 pub struct Generator<'a, T, R: 'a>
• src/librand/lib.rs:298 pub struct AsciiGenerator<'a, R: 'a>
• src/librand/lib.rs:334 pub struct XorShiftRng
• src/librand/lib.rs:420 pub struct Open01<F>(pub F);
• src/librand/lib.rs:428 pub struct Closed01<F>(pub F);

[nagisa]

What sense it makes to implement Debug for iterators? These can’t really show any useful state.

[seanmonstar]

If it truly doesn't make sense to implement for an iterator, it can be marked #[allow]. Others have suggested useful state they would like see, such as @bluss.

[bluss]

Any value that can end up being part of a user's data structure should have Debug. The slice iterator is the simplest example, but I don't think we can find a good excuse for any iterator.

[GuillaumeGomez]

I'll work on this a bit then.

[frewsxcv]

@seanmonstar Did you automatically generate the list above? If so, could you regenerate it to see what the current state of things is?

[seanmonstar]

@frewsxcv it was generated by setting #![warn(missing_debug_implementations)] in each of those crates, building, and then cleaning up the warning list.

[frewsxcv]

What sense it makes to implement Debug for iterators? These can’t really show any useful state.

From what I've seen, it is not uncommon for structures to have fields that are iterator structures. For me an end user, it's annoying that I can't just print the debug representation or derive Debug because one libstd structure (which the end user has no control over) doesn't implement Debug.

[frewsxcv]

These can’t really show any useful state.

For me, I don't really care if most Debug representations just display the name of the structure. That's plenty more helpful than not implementing Debug at all.