Ameba

Code style linter for Crystal

^{(a single-celled animal that catches food and moves about by extending fingerlike projections of protoplasm)}

About

Ameba is a static code analysis tool for the Crystal language. It enforces a consistent Crystal code style, also catches code smells and wrong code constructions.

How it works

Ameba's "fingerlike projections" are rules. Each rule makes the inspection for that or another problem in the source code. Currently rules are able to:

• simply validate lines of source code
• traverse AST using Crystal::Visitor
• tokenize sources using Crystal::Lexer and iterate through tokens
• do semantics analysis using Crystal::SemanticVisitor

Installation

As a project dependency:

Add this to your application's shard.yml:

development_dependencies:
  ameba:
    github: veelenga/ameba

Build bin/ameba binary within your project directory while running shards install.

You may also want to use it on Travis:

# .travis.yml
language: crystal
install:
  - shards install
script:
  - crystal spec
  - bin/ameba

Using this config Ameba will inspect files just after the specs run. Travis will also fail the build if some problems detected.

OS X

$ brew tap veelenga/tap
$ brew install ameba

From sources

$ git clone https://github.com/veelenga/ameba && cd ameba
$ make install

Usage

Run ameba binary within your project directory to catch code issues:

$ ameba
Inspecting 52 files.

.........................F.......F........F.........

src/ameba/ast/traverse.cr:27:5
PredicateName: Favour method name 'node?' over 'is_node?'

src/ameba/rules/empty_expression.cr:42:7
LiteralInCondition: Literal value found in conditional

src/ameba/rules/empty_expression.cr:30:7
UnlessElse: Favour if over unless with else

Finished in 10.53 milliseconds

52 inspected, 3 failures.

Configuration

Default configuration file is .ameba.yml. It allows to configure rule properties, disable specific rules and exclude sources from the rules.

Generate new file by running ameba --gen-config.

Inline disabling

One or more rules can't be disabled using inline directives:

# ameba:disable LargeNumbers
time = Time.epoch(1483859302)

time = Time.epoch(1483859302) # ameba:disable LargeNumbers

Writing a new Rule

Adding a new rule is as simple as inheriting from Ameba::Rule::Base struct and implementing a logic to detect a problem in the source file:

struct MySuperRule < Ameba::Rule::Base
  # This is a required method to be implemented by the rule.
  # Source will be passed here. If rule detects an issue in the source,
  # it reports an error:
  #
  #   source.error rule, location, message
  #
  def test(source)
    # TODO: test source
  end
end

As soon as a custom rule is defined, it becomes available in a full set of rules executed by default and also can be configured via config file:

MySuperRule:
  Enabled: false

Editor integration

• Vim: vim-crystal (via Syntastic)
• Emacs: ameba.el

Credits & inspirations

• Crystal Language
• Rubocop
• Credo
• Dogma

Contributors

• veelenga Vitalii Elenhaupt - creator, maintainer