Dialyzer (and Dialyxir) were written prior to compiler tracing, and also are based on Erlang's "Typespec" syntax which is a bit lacking.

I still use the Typespec syntax for its documentation benefits, and for catching "dumb" bugs, but as the Elixir compiler has improved I have found Dialyzer to be less relevant as the compiler usually catches things before Dialyzer would as it's not built into the compiler and isn't able to be.

> Does Dialyzer understand Elixir? Last I knew, it could only process Erlang source code and BEAM files.

Once compiled, it boils down to BEAM files that Dialyzer can understand, yes. And the [Dialyxir](https://dialyxir.hexdocs.pm) wrapper helps translating error messages in Elixir. But, there is a significant limitation compared to plain Erlang: Elixir protocols (which are quite used in core parts of the language) are not an Erlang construct, so Dialyzer will be clueless about them, just accepting any term. Enum.map(nil, & &foo/1) or to_string(%{}) will be invisible to it.

There's dialyxir which is wrapper to Dialyzer and I found it work fine on pure (non Phoenix) code.

As for how the problem manifests: even obvious contract violations stops being shown (making it feel like "Dialyzer is useless") but the second tell is very long check times (tens of seconds up to minutes).

  [W]hat happens when you run Dialyzer against BEAM files compiled from Elixir that has circular dependencies? Do its reports become more reliable, or does the reliability of those reports become irrelevant because the transformations the Elixir build system makes to your code make the structure of the BEAM code difficult to trace back to the Elixir source code?