How to hot reload a Vapor project

One question that gets frequently asked in Vapor’s Slack channel is whether is it possible to not have to recompile the entire project upon the slightest change in the source code. Until recently, I would have told you that this is just the unavoidable reality of compiled languages, but today I have a solution – sort of.

We all know that Swift Package Manager… well, while it works most of the time, it could really use some improvements: it could do more with the Package.swift than just to read it (what about adding new dependencies on-demand?), it could be more developer-friendly (swift package generate-xcodeproj, really? I still can’t believe that’s an actual command name 😱) and in general, it could… just be a little bit more like Ice, actually.

Ice is a much more user-friendly interface to Swift Package Manager while retaining a full compatibility with SPM, meaning you can mix and match SPM commands with Ice commands and your project should safely survive. Its output is clean and colourful^[1], it can add new dependencies to your Package.swift file as well as manage targets and projects. It even has its own small registry for all sorts of packages you can add to your project^[2]!

You are probably wondering why am I talking about some sort of SPM interface when I promised to be talking about hot reload? As it turns out, one of the features that SPM doesn’t have and Ice adds to the mix is watching the filesystem for changes and rebuilding your project anytime it detects one. You can do so by issuing the ice run -w command, where the -w stands for “watch”.

I’ve been playing with this feature on and off for the past few days and… while it’s useful, it’s definitely not perfect. Rebuilding a nearly empty project after a tiny change takes about ~25 seconds on my machine, which can lead to situations in which you expect the API to already include your latest changes when in fact, Swift is still building your project and preparing for relaunching your app.

So while it may not be a “hot reload” per se, it’s at the very least a “lukewarm reload” 🤣