Ameba

Code style linter for Crystal

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About

Ameba is a tool for enforcing a consistent Crystal code style, for catching code smells and wrong code constructions. Ameba's rules traverse AST and report bad parts of your code.

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 crystal deps.

You may want also use it on Travis:

language: crystal
install:
  - crystal deps
script:
  - crystal spec
  - bin/ameba

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

It is possible to configure or even disable specific rules using YAML configuration file. By default Ameba is looking for .ameba.yml in a project root directory. Copy and adjust existed example.

Write a new Rule

Adding a new rule is as simple as inheriting from Rule::Base struct and implementing your logic to detect a problem:

struct DebuggerStatement < Rule::Base
  # This is a required method to be implemented by the rule.
  # Source will be passed here. If rule finds an issue in this source,
  # it reports an error: 
  # 
  #   source.error rule, line_number, message
  #
  def test(source)
    # This line deletegates verification to a particular AST visitor.
    AST::Visitor.new self, source
  end

  # This method is called once the visitor finds a required node.
  def test(source, node : Crystal::Call)
    # It reports an error, if there is `debugger` method call
    # without arguments and a receiver. That's it, somebody forgot
    # to remove a debugger statement.
    return unless node.name == "debugger" && node.args.empty? && node.obj.nil?

    source.error self, node.location,
      "Possible forgotten debugger statement detected"
  end
end

Contributors

• veelenga Vitalii Elenhaupt - creator, maintainer