If your module A only depends on the struct of a module B, then we will only recompile A if the fields in the struct B change. But we always recompile the whole file the module is at. The beam of a module is always assembled as a unit.

A lot of it still comes from things like plugs and phoenix helpers, which are effectively fixed in the next Phoenix v1.4 version.

I like this talk and I think it’s good but it still doesn’t give me enough insight into our current compilation problems in a Phoenix project. We’ve ended up with a smaller version of the cited issue in the talk and recompilation currently takes 4-5 seconds which is enough to annoy us.

About the struct dependency bit; the speaker says this was changed. Does anyone know exactly how a struct dependency currently behaves in terms of recompilation? Does the Elixir compiler do analysis of struct-only changes or is it simply recompiling the module always regardless?

What I always wondered. If the compiler knows when to recompile which module, couldn’t that information be surfaced to the user? Like a “list me all modules, which are recompiled if module x changes (and why)”. mix xref is alreally nice, but even with all the knowledge about why and when modules depend on each other and need recompiling it’s still quite a lot of work to mitigate things in this space. I’ve had a few shots in a current project of mine and I while sometimes I found the spots to change I also had quite a few times, where I didn’t even find why modules would depend on each other even with the data xref produced. Maybe I should just try updating it to phoenix 1.4 and see how much it helps.

This information is already available via xref, no? So it is a bit unclear what you are asking for.

As I mention xref is already doing much, but I found it still hard to go from two modules being listed as dependant on one another to which part of my code is causing this dependency. Even more so if there’s no direct dependency, but rather up to a handful of intermediate modules in between. I’ve had cases where I sat in front of the xref output and wondered “how the **** are those things related to each other in my code”, where modules were handling totally different domains.