The official docs have limited support for it, if you search for i32[0] the default facet is "in names" but you can use the "in parameters" and "in return types" tabs for these. I don't know how well these handle abstract types and it's nowhere near hoogle convenience, but there you are (there were efforts to port/replicate hoogle a few years back but the few I remember seem to have been abandoned, specifying a search syntax is probably non-trivial as well given Rust's signatures are not as convenient as Haskell's there)/
[0] https://doc.rust-lang.org/std/?search=i32