elvis-core Build Status Stories in Ready

Erlang style reviewer core library.

This library includes the mechanism to apply rules to your code and their implementation.

Contributing & Reporting Bugs

If you find any bugs or have a problem while using this library, please open an issue in this repo (or a pull request :)).

The elvis repository is where all elvis_core related work is coordinated.


As a library

This library implements all the core functionality for analyzing files and applying the styles rules defined here or custom ones defined by its users.

The elvis command-line tool uses it extensively, so please check that project for a concrete example on how you could use for your own purposes.

Erlang Shell

After adding elvis_core as a dependency to your project and starting a shell, you will need to make sure the application is started:

{ok, _} = application:ensure_all_started(elvis_core).
%%= {ok,[ zipper, katana_code, elvis_core]}

Once this is done you can run the style rules in the following ways.

Load configuration from a file

ElvisConfig = elvis_config:from_file("elvis.config").
%%+ # src/elvis_core.erl [OK]
%%+ # src/elvis_result.erl [OK]
%%+ # src/elvis_style.erl [OK]
%%+ # src/elvis_utils.erl [OK]
%%= ok

This will try to load the configuration specified in an elvis.config located in the current directory. If no configuration is found invalid_config will be thrown.

Provide configuration as a value

Another option for using elvis_core from the shell is explicitly providing a configuration as an argument to rock/1:

ElvisConfig = [#{dirs => ["src"], filter => "*.erl", rules => []}],
%%+ # src/elvis_core.erl [OK]
%%+ # src/elvis_result.erl [OK]
%%+ # src/elvis_style.erl [OK]
%%+ # src/elvis_utils.erl [OK]
%%= ok

IMPORTANT: Config should have a valid format, but since this is a project under development the definition for valid format is still a work in progress. If the configuration format changes though, the example configuration files and the documentation in this README will be updated.

Output for failing rules

We have only presented results where all files were well-behaved (respect all the rules), so here's an example of how it looks when files break some of the rules:

# ../../test/examples/fail_line_length.erl [FAIL]
  - line_length
    - Line 14 is too long: "    io:format(\"This line is 81 characters long and should be detected, yeah!!!\").".
    - Line 20 is too long: "    io:format(\"This line is 90 characters long and should be detected!!!!!!!!!!!!!!!!!!\").".
# ../../test/examples/fail_no_tabs.erl [FAIL]
  - no_tabs
    - Line 6 has a tab at column 0.
    - Line 15 has a tab at column 0.
# ../../test/examples/small.erl [OK]


An elvis.config configuration file should look like this:

[ { elvis
  , [ { config
      , [ #{ dirs    => ["src"]
           , filter  => "*.erl"
           , ruleset => erl_files
        , #{ dirs    => ["."]
           , filter  => "Makefile"
           , ruleset => makefiles
        , #{ dirs    => ["."]
           , filter  => "rebar.config"
           , ruleset => rebar_config
        , #{ dirs    => ["."]
           , filter  => "elvis.config"
           , ruleset => elvis_config
      %% output_format (optional): how to format the output.
      %% Possible values are 'plain', 'colors' or 'parsable' (default='colors').
    , {output_format, colors}
      %% verbose (optional): when 'true' more information will
      %% be printed (default=false).
    , {verbose, true}
      %% no_output (optional): when 'true' nothing will be printed
      %% (default=false).
    , {no_output, false}
      %% parallel: determine how many files in parallel will be
      %% analyzed (default=1).
    , {parallel, 1}

Files, Rules & Rulesets

The dirs key is a list that indicates where elvis should look for the files that match filter, which will be run through each of the default rules in the specified ruleset, which is an atom.

If you want to override the default rules for a given ruleset you need to specify them in a rules key which is a list of items with the following structure {Module, Function, RuleConfig} or {Module, Function} if the rule takes no configuration values. You can also disable certain rules if you want to just by specifying the rule in the rules key and passing disable as its third parameter.

Disabling Rules

IMPORTANT: disable will only work if you also provided a ruleset as shown above.

Let's say you like your files to have a maximum of 90 characters per line and also you like to use tabs instead of spaces, so you need to override erl_files ruleset default rules as follows:

#{dirs => ["src"],
  filter => "*.erl",
  rules => [{elvis_style, line_length, #{limit => 90}}, %% change default line_length limit from 100 to 90
            {elvis_style, no_tabs, disable}], %% disable no_tabs rule
  ruleset => erl_files

Ignoring Modules

You can also ignore modules at a check level or at a ruleset (group of checks) level:

  • at check level by setting the ignore parameter in the rule you want to skip, e.g:

    {elvis_style, no_debug_call, #{ignore => [elvis, elvis_utils]}}

    There we are telling elvis to ignore elvis and elvis_utils modules when running no_debug_call check.

  • at ruleset level by setting the ignore group level option for the group you want to skip, e.g:

    #{dirs => ["src"],
      filter => "*.erl",
      ruleset => erl_files,
      ignore => [module1, module4]

    With this configuration, none of the checks for erl_files would be applied to module1.erl and module4.erl files.


output_format is used to configure the output format. Possible values are colors, plain and parsable. The latter could be use for the automated parsing and has a format very close to dialyzer in a form FILE:LINE:RULE:MESSAGE:

src/example.erl:1:god_modules:This module has too many functions (56). Consider breaking it into a number of modules.
src/example_a.erl:341:no_debug_call:Remove the debug call to io:format/2 on line 341.
src/example_a.erl:511:used_ignored_variable:Ignored variable is being used on line 511 and column 54.
src/example_a.erl:1252:used_ignored_variable:Ignored variable is being used on line 1252 and column 21.


It is possible to indicate elvis_core to produce more information in its output with the verbose option. The value provided should be a boolean, either true or false.

The default value for verbose is false.

On the other hand if no output is desired then the value for the no_output option should be true.

The default value for no_output is false.


In order to speed up the analysis of files, the parallel option can be used.

Its value indicates how many processes to use at the same time to apply the style rules to all the files gathered. The number provided should be less than or equal to the available CPUs, since any value higher than that won't report any speedup benefits.

The default value for parallel is 1.

Configuration Examples

You can find examples for configuration files in this project's config directory.

Implemented Rules

A reference of all rules implemented in Elvis can be found in this wiki page: Rules.

Custom Rules

The implementation of a rule is just a function that takes 3 arguments: elvis's config entry from its configuration; the file to be analyzed; and a configuration map specified for the rule. This means you can define rules of your own as long as the functions that implement them respect this arity.


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