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trappings: the outward signs, features, or objects associated with a particular situation, role, or thing.

"It had the trappings of success"

LintTrappings is a Ruby framework for writing static analysis command line tools (a.k.a. "linters"). It provides a large amount of functionality out of the box so that the uninteresting aspects of writing one of these tools (command line argument processing, configuration loading, file exclusion, etc.) are managed by the framework instead of yourself.

Development of LintTrappings was inspired by a number of static analysis tools I've built and maintained over the years, including scss-lint, haml-lint, and slim-lint. A common set of patterns and functionality began to appear, which have been extracted into this framework. It makes it far easier to get started writing your own automated static analysis tool.


  • Ruby 2.0+


Application Configuration

When creating your own application, you need to create a class that inherits LintTrappings::Application:

module MyApp
  class Application < LintTrappings::Application
    name                      'MyApp'
    executable_name           'my-app'
    version                   MyApp::VERSION

    configuration_file_names  %w[.my-app.yaml .my-app.yml]
    file_extensions           %w[txt text]

    # Specify the default configuration that all configurations extend.
    # The example below loads the file from your gem's config/default.yaml
    # (make sure you include it in your gemspec's `files` setting!)
                                  File.join(File.expand_path(File.join(File.dirname(__FILE__), '..', '..'))

    # Shown when an unhandled exception occurs so users know where to file issues
    home_url ''
    issues_url ''

    # Path to the directory in your gem where built-in linters are defined
    linters_directory         File.join(gem_dir, 'lib', 'my_app', 'linter')

    # Class to use when figuring out all registered linters
    # (any subclass of this class is a registered linter).
    # Even if your base linter class has no custom logic, you still need to
    # define one to make sure your linter hierarchy is explorable.
    linter_base_class MyApp::Linter

    # Class to use to parse documents that will be linted.
    # Your implementation needs to define the `process_source` method.
    document_class MyApp::Document

Configuration File

LintTrappings supports a large collection of configuration options in your application's YAML file. These are values that can be tweaked by the users of your application without you having to write any code–they all work out of the box.

# List of configuration files to extend. These files will be loaded and
# merged with each other in order from first to last (last wins if they
# define values for the same configuration key), and finally will be merged
# with this configuration file.
# This is useful if you want to break apart your configuration into separate
# components for organizational purposes.
# The files are loaded relative to the location of this configuration file
# if the paths are not absolute.
  - 'some/config/file.yaml'
  - 'some/other/config/file.yaml'

# The types of severities that can be reported, and whether or not they
# would result in a warning or a failed run. A warning would still result
# in a successful exit status (zero), while a failure would result in
# a non-zero exit status and would thus fail in a test environment or CI.
  refactor: warn
  warning: warn
  error: fail
  fatal: fail

# If no severity is explicitly specified in a linter's configuration, any
# problem reported by the linter is assigned this severity.
default_severity: error

# If a linter raises an exception (which is always a bug), treat the error
# as a lint with this level of severity.
linter_exception_severity: error

# If an error occurs parsing a document (i.e. due to syntax error), treat
# the error as a lint with this level of severity.
parse_exception_severity: error

# Defines the list of extensions of files to include when recursively searching
# under directory paths. This allows you to specify directories in your
# `include`/`exclude` paths without needing the `**/*.ext` glob.
  - txt
  - text

# Define a list of paths to include/exclude from linting.
# A path can be a directory or a file. Matching directories result in a
# recursive scan.
  - 'some-file.txt'
  - 'some/directory/path'
  - 'some/glob/for/files/*.txt'
  - 'some-other-file.txt'
  - 'everything/under/this/directory/excluded'
  - 'every/txt/file/under/this/directory/excluded/**/*.txt'

# AVOID USING THESE (provided for users with weird file names)
# Define an explicit list of literal paths to include/exclude from linting.
# A path can be a directory or a file. Prefer the `include`/`exclude`
# options as those allow you to specify globs. Use these options if
# your files have glob characters in their name which you need to match
# against. (`*`,`{`, etc.)
  - some/directory/path
  - some*file.txt # <- "*" treated as a literal asterisk in this context!
  - 'some/directory/path'
  - 'some*file.txt' # <- "*" treated as a literal asterisk in this context!

# List of directories to load custom linter implementations from. This allows
# developers to easily write their own one-off custom linters for a repository.
# Directories are recursively scanned for `*.rb` files, so make sure you keep
# only linter implementations in that directory, and no other Ruby files!
# If you find yourself needing the same custom linters in multiple projects,
# you should pull them out into a separate gem and load it via the
# `linter_plugins` option.
  - custom-linters
  - path/to/more/linters

# List of paths to load via `require`. Will load any linter implementations
# and also extend any configuration defined in the gem. Note that this allows
# you to ship gems that only contain configuration, allowing you to reuse
# configuration across multiple projects.
# See the documentation on creating a reusable gem for how to create your own.
  - my_custom_linters
  - more_custom_linters

# A collection of all linter configurations. This will be the main point of
# configuration for most users of your application. Linter names must match
# their class name in both spelling and case.

# This can be used to configure built-in linters as well as any custom linters
# loaded via the `linter_directories` or `linter_plugins` options.
# Values specified here will overwrite values specified in configurations
# loaded via `extends` or `linter_plugins`, so this file has the final say.
    enabled: true     # If false, skips running this linter
    severity: warning # If unspecified, defaults to `default_severity`

    # Custom options are set here; run `my-app --show-docs MyLinter` to see
    # documentation of all options available to a given linter.
    some_option: true

    include: # List of file paths to include. The linter will ignore all others.
      - 'some/file.txt'
      - 'some/directory'
    exclude: # List of file paths to exclude. The linter will ignore any of these.
      - 'some/other/file.txt'
      - 'some/nested/**/directory'


# Specifies the command that should be run to transform files before they are
# linted. Command will be passed the content of the file via the standard input
# stream and anything sent to the standard output stream will be passed to the
# linter.
# Remember that if your preprocessing alters the file such that line numbers
# change, then the linter may report line numbers that are different from the
# original file.
preprocess_command: "sed '1,2s/---//'" # Removes Jekyll front matter

# By default `preprocess_command` enables the preprocessor for all files. To
# only preprocess certain files, add paths/glob patterns to this list.
  - 'path/to/files/to/preprocess'
  - 'another/path/**/*.txt'

Command Line Flags

Any LintTrappings-powered application also supports the following flags out of the box:

Flag Description
-c/--config-file path Specify which configuration file to use
-e/--exclude-path path Add a path to be excluded (can use flag multiple times)
-f/--format FormatterName Specify which output format you want. Combine with the --out flag to redirect to a file (can use flags multiple times to write different formats to different output files).
-o/--out path Redirect the last specified formatter (via --format) to a file. If no formatter has been specified, redirects the default format output to the specified file.
--stdin-file-path path When passing a file to the linter via standard input, treat the file as having this path (so relevant configuration can be applied). Only a single file at a time can be linted this way, but it is useful for integrations with text editor plugins.
-r/--require library-path Specify a path to a Ruby library/file to be required via Kernel.require. This allows you to load third-party formatters or other integrations.
-i/--include-linter LinterName Specify a specific linter to run (can use flag multiple times to specify multiple linters). This disregards any linters enabled/disabled by your configuration file.
-x/--exclude-linter LinterName Specify a linter to exclude (can use flag multiple times to exclude multiple linters) in addition to the linters disabled by your configuration file.
-p/--plugin library-path Load a Ruby library containing a third-party linter plugin (typically packaged as a gem).
--linter-dir path Load custom linters from a directory (will load files recursively in subdirectories). Can specify multiple times for different directories.
-C/--concurrency num-workers Configure the number of processes to use when linting files. Must be a non-zero positive integer.
--show-linters Display available/loaded linters and whether or not they are enabled.
--show-formatters Display available/loaded formatters.
--show-docs [LinterName] Display documentation for all linters, including their configurable options. Can optionally specify a linter to show documentation for only that linter.
--[no-]color Whether or not to output colorized text. Color is enabled by default if the standard output stream is a TTY.
-d/--debug Display additional debug information (for example, the stack trace when a linter raises an unhandled exception).
-h/--help Display a list of all command line options.
-v/--version Display the application version.
-V/--verbose-version Display the application version as well as information about the Ruby runtime and LintTrappings gem version.


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We love getting feedback with or without pull requests. If you do add a new feature, please add tests so that we can avoid breaking it in the future.

Change History

If you're interested in seeing the changes and bug fixes between each version of LintTrappings, read the LintTrappings Change History.


This project is released under the MIT license.