merlin VS cargo-up

Merlin: Context sensitive completion for OCaml in Vim and Emacs\ (0 comments)

Instead of searching functions based on their type structure (like Hoogle), you could search for functions that "consume"/"produce" values of given types (like OCaml's Merlin). I think Rust already computes variance of type constructors, so such a tool just would have to obtain this information.

However, after posting this question I stumbled upon this Github issue where they say it isn't supposed to work out of the box and you're supposed to bind a key to it by editing your .emacs file. Turns out the default .emacs file binds auto-complete to "backtab" which means Shift+Tab but that didn't work. I did eventually discover that I can get some kind of completion by binding backtab to completion-at-point like this:

Self-advertising: I partcipated to the writing of Merlin: A Language Server for OCaml (Experience Report), which explains the overall design of Merlin, a language server for OCaml. A key idea of Merlin are that classic lexing-parsing-typing pipelines can easily be adapted to be incremental for a Language Server, especially when they are using immutable data structures.

It should be possible. I've only tinkered around with ra for a project similar to cargo-up. But the API provides the needed entrypoints to do that kind of analysis IIRC.