Support search by return type in rustdoc

[mdinger]

The idea came from here. For example, to find types which return Chunks I would expect you would search fn: -> Chunks in the rustdoc search bar.

cc @pornel @tomjakubowski

[kornelski]

It's good to have an advanced option, but in my original case it probably wouldn't have helped me, because I didn't know the search supported advanced syntax at all.

Something more discoverable would have helped me, e.g. if search for "Chunks" by default also matched return types. If that's too noisy, then it could be a sort of faceted search letting me choose whether I want function names, argument types or return types.

[mitaa]

This seems to kind of work currently ("-> box", "-> usize"), though I think this should be improved since the type-name in the search index seems to be very trimmed-down or omitted in most cases for some reason. (i.e. the original example doesn't work; "-> Chunks")

[bluss]

-> Chunks only matches functions with 0 input arguments, because it matches the input arguments exactly too with that search.

[mitaa]

@bluss
Thanks, it seems like it shouldn't be too hard to extend the syntax for this use-case then. Something like ... -> Chunks or * -> Chunks maybe.

[mitaa]

This has now been implemented in #31639 using * -> T

[bluss]

nice, I'll have to try it out.

[bluss]

Fixed in #31639