Dialyxir

Mix tasks to simplify use of Dialyzer in Elixir projects.

Changes in 0.4 and 0.5

If you’ve been using earlier versions of Dialyxir there are some changes you may need to make in the configuration of your existing projects. A summary of the most common issues and changes are found in the Wiki pages for 0.4 and 0.5.

Quickstart

If you are planning to use Dialyzer with an application built with the Phoenix Framework, check out the Quickstart wiki.

Installation

Dialyxir is available on hex.pm.

You can either add it as a dependency in your mix.exs, or install it globally as an archive task.

To add it to a mix project, just add a line like this in your deps function in mix.exs:

defp deps do
  [{:dialyxir, "~> 0.5", only: [:dev], runtime: false}]
end

mix do deps.get, deps.compile

To install globally as an archive:

git clone https://github.com/jeremyjh/dialyxir
cd dialyxir
MIX_ENV=prod mix do compile, archive.build, archive.install

Usage

Use dialyxir from the directory of the mix project you want to analyze; a PLT file will be created or updated if required and the project will be automatically compiled.

mix dialyzer

Command line options

--no-compile - do not compile even if needed.
--no-check - do not perform (quick) check to see if PLT needs updated.
--halt-exit-status - exit immediately with same exit status as dialyzer. useful for CI. do not use with mix do.
--plt - only build the required plt(s) and exit.

Warning flags passed to this task are passed on to :dialyzer.

e.g.

`mix dialyzer --unmatched_returns`

With Explaining Stuff

Dialyzer is a static analysis tool for Erlang and other languages that compile to BEAM bytecode for the Erlang VM. It can analyze the BEAM files and provide warnings about problems in your code including type mismatches and other issues that are commonly detected by static language compilers. The analysis can be improved by inclusion of type hints (called specs) but it can be useful even without those. For more information I highly recommend the Success Typings paper that describes the theory behind the tool.

Usage is straightforward but you should be aware of the available configuration settings you may wish to add to your mix.exs file.

PLT

The Persistent Lookup Table (PLT) is basically a cached output of the analysis. This is important because you’d probably stab yourself in the eye with a fork if you had to wait for Dialyzer to analyze all the standard library and OTP modules you are using everytime you ran it. Running the mix task dialyzer by default builds several PLT files:

A core Erlang file in $MIX_HOME/dialyxir_erlang-[OTP Version].plt
A core Elixir file in $MIX_HOME/dialyxir_erlang-[OTP Version]_elixir-[Elixir Version].plt
A project environment specific file in _build/env/dialyze_erlang-[OTP Version]_elixir-[Elixir Version]_deps-dev.plt

The core files are simply copied to your project folder when you run dialyxir for the first time with a given version of Erlang and Elixir. By default, all the modules in the project PLT are checked against your dependencies to be sure they are up to date. If you do not want to use MIX_HOME to store your core Erlang and Elixir files, you can provide a :plt_core_path key with a file path. You can specify a different location for the project PLT file with the :plt_file keyword - this is deprecated because people were using it with the old dialyxir to have project-specific PLTs, which are now the default. To silence the deprecation warning, specify this value as plt_file: {:no_warn, "/myproject/mypltfile"}.

The core PLTs include a basic set of OTP applications, as well as all of the Elixir standard libraries. The apps included by default are [ :erts, :kernel, :stdlib, :crypto].

If you don’t want to include the default apps you can specify a :plt_apps key and list there only the apps you want in the PLT. Using this option will mean dependencies are not added automatically (see below). If you want to just add an application to the list of defaults and dependencies you can use the :plt_add_apps key.

Dependencies

OTP application dependencies are (transitively) added to your PLT by default. The applications added are the same as you would see displayed with the command mix app.tree. There is also a :plt_add_deps option you can set to control the dependencies added. The following options are supported:

:project - Direct Mix and OTP dependencies
:apps_direct - Only Direct OTP application dependencies - not the entire tree
:transitive - Include Mix and OTP application dependencies recursively
:app_tree - Transitive OTP application dependencies e.g. mix app.tree (default)

The example below changes the default to include only direct OTP dependencies, and adds another specific dependency to the list. This can be helpful if a large dependency tree is creating memory issues and only some of the transitive dependencies are required for analysis.

def project do
 [ app: :my_app,
   version: "0.0.1",
   deps: deps,
   dialyzer: [plt_add_deps: :apps_direct, plt_add_apps: [:wx]]
 ]
end

Flags

Dialyzer supports a number of warning flags used to enable or disable certain kinds of analysis features. Until version 0.4, dialyxir used by default the additional warning flags shown in the example below. However some of these create warnings that are often more confusing than helpful, particularly to new users of Dialyzer. As of 0.4, there are no longer any flags used by default. To get the old behavior, specify them in your Mix project file. For compatibility reasons you can use eiher the -Wwarning convention of the dialyzer CLI, or (preferred) the WarnOpts atoms supported by the API. e.g.

def project do
 [ app: :my_app,
   version: "0.0.1",
   deps: deps,
   dialyzer: [ flags: ["-Wunmatched_returns", :error_handling, :race_conditions, :underspecs]]
 ]
end

Paths

By default only the ebin in the _build directory for the current mix environment of your project is included in paths to search for BEAM files to perform analysis on. You can specify a list of locations to find BEAMS for analysis with :paths keyword.

def project do
 [ app: :my_app,
   version: "0.0.1",
   deps: deps,
   dialyzer: [plt_add_apps: [:mnesia],
             flags: [:unmatched_returns,:error_handling,:race_conditions, :no_opaque],
             paths: ["_build/dev/lib/my_app/ebin", "_build/dev/lib/foo/ebin"]]
 ]
end

Ignore Warnings

By default dialyxir has always included the :unknown warning option so that warnings about unknown functions are returned. This is usually a clue that the PLT is not complete and it may be best to leave it on, but it can be disabled entirely by specifying remove_defaults: [:unknown] in your config.

A better option is to ignore the specific warnings you can’t fix (maybe due to a bug upstream, or a dependency you just don’t want to include in your PLT due to time/memory in building the PLT file.)

If you want to ignore well-known warnings, you can specify a file path in :ignore_warnings.

def project do
 [ app: :my_app,
   version: "0.0.1",
   deps: deps,
   dialyzer: [ignore_warnings: "dialyzer.ignore-warnings"]
 ]
end

Any line of dialyzer output (partially) matching a line in "dialyzer.ignore-warnings" is filtered.

For example, in project where mix dialyzer outputs:

  Proceeding with analysis...
config.ex:64: The call ets:insert('Elixir.MyApp.Config',{'Elixir.MyApp.Config',_}) might have an unintended effect due to a possible race condition caused by its combination withthe ets:lookup('Elixir.MyApp.Config','Elixir.MyApp.Config') call in config.ex on line 26
config.ex:79: Guard test is_binary(_@5::#{'__exception__':='true', '__struct__':=_, _=>_}) can never succeed
config.ex:79: Guard test is_atom(_@6::#{'__exception__':='true', '__struct__':=_, _=>_}) can never succeed
 done in 0m1.32s
done (warnings were emitted)

If you wanted to ignore the last two warnings about guard tests, you could add to dialyzer.ignore-warnings:

Guard test is_binary(_@5::#{'__exception__':='true', '__struct__':=_, _=>_}) can never succeed
Guard test is_atom(_@6::#{'__exception__':='true', '__struct__':=_, _=>_}) can never succeed

And then run mix dialyzer would output:

  Proceeding with analysis...
config.ex:64: The call ets:insert('Elixir.MyApp.Config',{'Elixir.MyApp.Config',_}) might have an unintended effect due to a possible race condition caused by its combination withthe ets:lookup('Elixir.MyApp.Config','Elixir.MyApp.Config') call in config.ex on line 26
 done in 0m1.32s
done (warnings were emitted)

:ignore_warnings works as you may expect with --halt-exit-status - by resetting the exit status to 0 if all warnings are filtered.

Dialyxir

v0.5.1

Dialyxir

Changes in 0.4 and 0.5

Quickstart

Installation

Usage

Command line options

With Explaining Stuff

PLT

Dependencies

Flags

Paths

Ignore Warnings