Dialyzex - an alternative Mix task for dialyzer

I was just playing with adding dialyxir to a CI build; now I’m evaluating this instead (for that layered PLT caching)!

QQ: I’m running mix dialyzer --check=false on my project but I’m seeing warnings coming from my Elixir install and project dependencies themselves. I thought the check flag was meant to suppress that behaviour, do I have it wrong?

The thing I think all of these dialyzer packages could use is a “Getting Started” guide that handles a bunch of common issues that show up when using it with Elixir. I’ve tried to use it on various projects before and it raises all kinds of issues about protocols, various functions that are missing, etc.

I can get used to reading the erlang output of the errors themselves, I just don’t know what to do with all the “missing function x” stuff where x definitely exists.

Ah, I just found this behaviour (the persistent dependency warnings despite --check=false being set) explained under the caveats section.

Perhaps an additional mix dialyzer.clean task could assist with this? I’ve wished for a similar task through dialyxir before too. It’d be nice to not have to know how the specific dialyzer package in use has built its plts and where it’s stashed them to get a clean read.

That’s a great idea! Would you file it as a feature request on the Github repo?

Thanks for that comment, Ben. One thing that I personally forget sometimes is that I’ve worked for a long time with Dialyzer and understand most of the warnings. I’ll prepare a guide to them soon.

--check=false disables validation of the existing PLTs. You’ll still have to build them at least once. In a CI build, I would not use that flag.

Done, and cross-referenced!

So should I separate building my PLTs from checking my project in a CI environment, somehow?

My understanding is if I invoke mix dialyzer as a CI job (without the flag), and persist the ~/.cache folder between runs, the first time it will build 3 PLTs: ones for erlang, Elixir, and the deps. Then it will perform checks, but since the PLTs were built without the check flag upstream warnings will fail my build.

When I set this to false it will never fail my build because of issues in upstream PLTs, whether or not this is the first time creating them, which seems like the desired behaviour during CI, is there a more correct way to set this up that you recommend?

That would be incredibly useful, thank you!

I would love this. What do you think about placing such a guide as its own page, alongside the typespec docs, within Elixir docs itself?

It doesn’t seem efficient to have every dialyzer package owner author their own guide, since the warnings are identical across packages; it makes more sense to me if they all could just link to an upstream Elixir guide.

That’s an excellent idea. I will start authoring one myself, but it could ultimately live in the Elixir documentation.