The language server has code actions for adding and update the signatures (see https://github.com/julia-vscode/LanguageServer.jl/pull/1084 and https://github.com/julia-vscode/LanguageServer.jl/pull/1094).
Here is what this looks like in neovim:
If you are using VS Code I think these actions show up as a 
when you hover over the function signature.