Classic Simon Peyton-Jones slide on "the power of the dot". I think everyone realizes on some level that this is the best part of OO, but curiously few acknowledge it explicitly. (source: microsoft.com/en-us/research)
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Lean lets you use `.` for this stuff - not sure how good the autocompletion is like though, although the editor integration is really nice.
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In general FP languages tend to be super great at hole-driven development tooling where you're refining programs with missing parts, based on the expected type. It's a bit different to the OOP approach though. Agda, Haskell, and Idris use this style.
This is something I wish Rust had - the ability to have 'typed holes' in expressions and patterns that you could interact with via your editor. For example interacting with `match` is kind of a chore without it :(