ex_check v0.11.0 mix check View Source

One task to efficiently run all code analysis & testing tools in an Elixir project.


Task comes out of the box with a rich predefined set of curated tools that are considered to be reasonable additions for most Elixir and Phoenix projects which care about having bug-free, maintainable and secure code.

Following curated tools are configured by default:

  • :compiler - produces compilation warnings that allow to early detect bugs & typos in the code eg. an attempt to call non-existing or deprecated function

  • :formatter - ensures that all the code follows the same basic formatting rules such as maximum number of chars in a line or function indentation

  • :ex_unit - starts the application in test mode and runs all runtime tests against it (defined as test modules or embedded in docs as doctests)

  • :credo - ensures that all the code follows a further established set of software design, consistency, readability & misc rules and conventions (still statical)

  • :sobelow - performs security-focused static analysis mainly focused on the Phoenix framework, but also detecting vulnerable dependencies in arbitrary Mix projects

  • :dialyzer - performs static code analysis around type mismatches and other issues that are commonly detected by static language compilers

  • :ex_doc - compiles the project documentation in order to ensure that there are no issues that would make it impossible for docs to get collected and assembled

  • :npm_test - runs JavaScript tests in projects with front-end assets embedded in assets directory and package.json in it (default for Phoenix apps)

You can disable or adjust curated tools as well as add custom ones via the configuration file.


  1. :compiler tool is run before others in order to compile the project just once and to avoid reprinting the compilation error multiple times.

  2. If the compilation succeded (even if with warnings), further tools are run in parallel while their output is streamed live one by one for instant insight.

  3. Output from tools that have failed gets reprinted for sake of easily reading into them all at once and identifying all project issues in one go.

  4. Summary is presented with a list of all tools that have failed, succeeded or were skipped due to missing files or project dependencies.

  5. If any of the tools have failed, the Erlang system gets requested to emit exit status 1 upon shutdown in order to make the CI build fail.

Tool order

Tools are run in parallel, but their output is presented one by one in order to avoid mixing it up. You can control the order in which the output is presented for tools that have started at the same time via the :order tool option. You'll probably want to put tools that run quicker and fail more often before the others in order to get useful feedback as soon as possible. Curated tools are ordered in such a way out of the box.

Tool processes and ANSI formatting

Tools are run in separate processes. This has following benefits:

  • allows to run tools in parallel & stream their output
  • catches exit statuses in order to detect failures
  • enables running Mix tasks in multiple envs
  • enables including non-Elixir scripts and tools in the check

The downside is that tools will be run outside of TTY which will usually result in disabling ANSI formatting. This issue is fixed in different ways depending on Elixir version:

  • Elixir 1.9 and newer: patches all Elixir commands and Mix tasks with --erl-config option to load the Erlang configuration provided by ex_check that sets the ansi_enabled flag

  • older versions: patches Mix tasks with --eval option to run Application.put_env/3 that sets the ansi_enabled flag

You may keep your Elixir commands unaffected via the :enable_ansi tool option. It's ignored for non-Elixir tools for which you'll have to enforce ANSI on your own.

Cross-tool dependencies

Even though tools are run in parallel, it's possible to make sure that specific tool will be run only after other(s) are completed via the :run_after tool option. This enables defining complex workflows in which tools may reuse artifacts from ones executed earlier or they may be forced not to run at the same time without giving up on entire parallel execution.

Note that tools will be run regardless of the exit status of their :run_after dependencies, but they'll be skipped if their dependencies won't be run at all e.g. due to using --except command line option or a missing/circular dependency.

Umbrella projects

Task comes with extensive support for umbrella projects. The most notable feature is the ability to run tools recursively for each child app separately. It's similar to flagging Mix tasks as recursive but empowered with following extra benefits:

  • runs recursively not just Mix tasks, but also arbitrary scripts & commands
  • runs tools on child apps in parallel
  • allows tools to target only specific child apps
  • presents failures & run durations for each child app separately
  • detects if curated tools should run for each child app separately
  • builds separate cross-tool dependency chains for each child app

You may want to disable parallel execution of the tool on child apps (parallel: false under :umbrella tool option) if it uses the same resources across tool runs against different child apps. An example of that could be ex_unit that, depending on a project and test dependencies, may involve mutating the same database in test suites belonging to separate child apps.

You may have the tool run only at the root level of the umbrella by disabling the recursive execution (recursive: false under :umbrella tool option) and targeting an empty list of child apps (apps: [] under :umbrella tool option).

Configuration file

Check configuration may be adjusted with the optional .check.exs file. Task will load the configuration in following order:

  1. Default stock configuration.
  2. .check.exs in user home directory.
  3. .check.exs in current project directory (or umbrella root for an umbrella project).

Configuration file should evaluate to keyword list with following options:

  • :parallel - toggles running tools in parallel (default: true)
  • :skipped - toggles printing skipped tools in summary (default: true)
  • :tools - a list of tools to run (default: curated tools)

Each tool is a {:tool_name, opts} tuple where opts is a keyword list with following options:

  • :enabled - enables/disables already defined tools (default: true)
  • :command - command as string or list of strings (executable + arguments)
  • :cd - directory (relative to cwd) to change to before running the command
  • :env - environment variables as map with string keys & values
  • :order - integer that controls the order in which tool output is presented (default: 0)
  • :run_after - list of tool names (atoms) as deps that must finish running before tool start
  • :enable_ansi - toggles extending Elixir/Mix commands to have ANSI enabled (default: true)
  • :umbrella - configures the tool behaviour in an umbrella project

Umbrella configuration under :umbrella key is a keyword list with following options:

  • :recursive - toggles running the tool on each child app separately as opposed to running it once from umbrella root (default: true except for non-recursive Mix tasks)
  • :parallel - toggles running tool in parallel on all child apps (default: true)
  • :apps - list of umbrella child app names targeted by the tool (default: all apps)

You may also use one of the shorthand tool tuple forms:

  • {:tool_name, enabled} where enabled corresponds to the :enabled option
  • {:tool_name, command} where command corresponds to the :command option
  • {:tool_name, command, opts} where command corresponds to the :command option

Use the mix check.gen.config task to generate sample configuration that comes with well-commented examples to help you get started.

Command line options

  • --only dialyzer --only credo ... - run only specified check(s)
  • --except dialyzer --except credo ... - don't run specified check(s)
  • --no-parallel - don't run tools in parallel
  • --no-skipped - don't print skipped tools in summary