rustdoc "Aliased Type" view is wrong

[SludgePhD]

In this rustdoc output, rustdoc seems to claim that MatrixView aliases a struct MatrixView.

This is wrong, since no such struct exists. It seems like there was some sort of mistake when implementing this feature that ended up using the wrong name there? It should say Matrix instead.

[aDotInTheVoid]

What crate is this for? Can you give a minimal example that reproduces this behavior?

[SludgePhD]

Any type alias of a struct will reproduce it.

pub type Alias<T> = Vec<T>;

Result:

[fmease]

This works exactly as intended: The “aliased type” shown isn't a real user-written type but a synthetic one.

[fmease]

Of course, we should probably employ some more heuristics and e.g., not show aliased structs whose fields are all private.

[fmease]

I can understand that that feature might be a bit unintuitive at first. If you have suggestions for making it clearer to the reader that this aliased type isn't grounded in source code, please don't hesitate to share them :)

[SludgePhD]

To me, "aliased type" strictly refers to the right-hand side of the type A = B syntax, so I would find this feature much less confusing if it simply used the name of the right-hand type instead.

[Urgau]

To me, "aliased type" strictly refers to the right-hand side of the type A = B syntax, so I would find this feature much less confusing if it simply used the name of the right-hand type instead.

@SludgePhD Except that this wouldn't work in "generic context", take for exemple this type alias:

type NonZeroU128 = NonZero<u128>;

writting it with the "right hand side" would mean:

struct NonZero<u128>(/* ... */);

which is not a valid syntax and is not that what anyone that would use NonZeroU128 would need to know.

Taking a more expressive example:

struct Container<A: Trait>(pub A, pub A);
type MyContainer = Container<MyStruct, MyStruct>;

Here, the aliased type (as seen by the compiler) is:

struct MyContainer(pub MyStruct, pub MyStruct);

and it makes much more sense to write it like this. That way users don't have the irrelevant Trait bound or even the generic in the way.

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You can look at the description of #114855 for a more detailed explanation and motivation for the "aliased type" feature.

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As for how we can improve the reading of this section, what about a tooltip (or small label) with something like this:

This section shows the concrete type (i.e. removing any generics/bounds not present the aliased type) has would been seen by anyone using the aliased type.

[lolbinarycat]

I think the logical change here would be to change the "Aliased Type" heading to something like "Effective Type" or something. This wouldn't be the first time rustdoc has made significant wording changes (see the whole "Trait Object") thing.