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 crystal deps.

You may also want to use it on Travis:

# .travis.yml
language: crystal
install:
  - crystal deps
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 or even disable specific rules. Simply copy and adjust existed sample. Each rule is enabled by default, even if you remove it from the config file.

Writing 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 callback in the AST visitor.
    AST::Visitor.new self, source
  end

  # This method is called once the visitor finds a needed 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

Credits & inspirations

• Crystal Language
• Rubocop
• Credo
• Dogma

Contributors

• veelenga Vitalii Elenhaupt - creator, maintainer