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https://github.com/Shopify/erb_lint

Lint your ERB or HTML files
https://github.com/Shopify/erb_lint

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Lint your ERB or HTML files

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# ERB Lint [![Build Status](https://github.com/Shopify/erb_lint/workflows/Tests/badge.svg)](https://github.com/Shopify/erb_lint/actions)



`erb_lint` is a tool to help lint your ERB or HTML files using the included linters or by writing your own.



## Requirements



* Ruby 2.3.0+

 - This is due to use of the safe navigation operator (`&.`)

 - This is also due to the use of the tilde-heredoc `<<~` syntax in some tests.



## Installation



```bash

gem install erb_lint

```



...or add the following to your `Gemfile` and run `bundle install`:



```ruby

gem 'erb_lint', require: false

```



## Configuration



Create a `.erb_lint.yml` file in your project, with the following structure:



```yaml

---

EnableDefaultLinters: true

linters:

  ErbSafety:

    enabled: true

    better_html_config: .better-html.yml

  Rubocop:

    enabled: true

    rubocop_config:

      inherit_from:

        - .rubocop.yml

```



See below for linter-specific configuration options.



## Usage



This gem provides a command-line interface which can be run like so:



1. Run `erb_lint [options]` if the gem is installed standalone.

2. Run `bundle exec erb_lint [options]` if the gem is installed as a Gemfile dependency for your app.



For example, `erb_lint --lint-all --enable-all-linters` will run all available

linters on all ERB files in the current directory or its descendants (`**/*.html{+*,}.erb`).



If you want to change the glob & exclude that is used, you can configure it by adding it to your config file as follows:



```yaml

---

glob: "**/*.{html,text,js}{+*,}.erb"

exclude:

  - '**/vendor/**/*'

  - '**/node_modules/**/*'

linters:

  ErbSafety:

    enabled: true

    better_html_config: .better-html.yml

  Rubocop:

    enabled: true

    rubocop_config:

      inherit_from:

        - .rubocop.yml

```



Make sure to add `**/` to exclude patterns; it matches the target files' absolute paths.



## Enable or disable default linters

`EnableDefaultLinters`: enables or disables default linters. [Default linters](#linters) are enabled by default.



## Disable rule at offense-level

You can disable a rule by placing a disable comment in the following format:



Comment on offending lines

```.erb

 <%# erb_lint:disable SelfClosingTag %>

```



To raise an error when there is a useless disable comment, enable `NoUnusedDisable`.



To disable inline comments and report all offenses, set `--disable-inline-configs` option.



## Exclude



You can specify the exclude patterns both of global and lint-local.



```yaml

---

exclude:

  - '**/global-lib/**/*'

linters:

  ErbSafety:

    exclude:

      - '**/local-lib/**/*'

```



## Linters



| Available Linters                                | Default  | Description |

| ------------------------------------------------ |:--------:|-------------|

| [AllowedScriptType](#allowedscripttype)          | Yes      | prevents the addition of `` tags that have `type` attributes that are not in a white-list of allowed values |

| ClosingErbTagIndent                              | Yes      |             |

| [CommentSyntax](#commentsyntax)                  | Yes      | detects bad ERB comment syntax |

| ExtraNewline                                     | Yes      |             |

| [FinalNewline](#finalnewline)                    | Yes      | warns about missing newline at the end of a ERB template |

| [NoJavascriptTagHelper](#nojavascripttaghelper)  | Yes      | prevents the usage of Rails' `javascript_tag` |

| ParserErrors                                     | Yes      |             |

| PartialInstanceVariable                          | No       | detects instance variables in partials |

| [RequireInputAutocomplete](#requireinputautocomplete)        | Yes       | warns about missing autocomplete attributes in input tags |

| [RightTrim](#righttrim)                          | Yes      | enforces trimming at the right of an ERB tag |

| [SelfClosingTag](#selfclosingtag)                | Yes      | enforces self closing tag styles for void elements |

| [SpaceAroundErbTag](#spacearounderbtag)          | Yes      | enforces a single space after `<%` and before `%>`|

| SpaceIndentation                                 | Yes      |             |

| SpaceInHtmlTag                                   | Yes      |             |

| TrailingWhitespace                               | Yes      |             |

| [DeprecatedClasses](#deprecatedclasses)          | No       | warns about deprecated css classes |

| [ErbSafety](#erbsafety)                          | No       | detects unsafe interpolation of ruby data into various javascript contexts and enforce usage of safe helpers like `.to_json`. |

| [Rubocop](#rubocop)                              | No       | runs RuboCop rules on ruby statements found in ERB templates |

| [RequireScriptNonce](#requirescriptnonce)        | No       | warns about missing [Content Security Policy nonces](https://guides.rubyonrails.org/security.html#content-security-policy) in script tags |

| [HardCodedString](#hardcodedstring)              | No       | warns if there is a visible hardcoded string in the DOM (does not check for a hardcoded string nested inside a JavaScript tag)            |



### DeprecatedClasses



DeprecatedClasses will find all classes used on HTML elements and report any classes that violate the rule set that you provide.



A `rule_set` is specified as a list, each with a set of `deprecated` classes and a corresponding `suggestion` to use as an alternative.



Example configuration:



```yaml

---

linters:

  DeprecatedClasses:

    enabled: true

    exclude:

      - 'app/views/shared/deprecated/**'

    addendum: "See UX wiki for help."

    rule_set:

      - deprecated: ['badge[-_\w]*']

        suggestion: "Use the ui_badge() component instead."

```



You can specify an `addendum` to be added to the end of each violation.

The error message format is: `"Deprecated class ... #{suggestion}"`

or `"Deprecated class ... #{suggestion} #{addendum}"` if an `addendum` is present.



Linter-Specific Option | Description

-----------------------|-----------------------------------------------------------------------------------

`rule_set`             | A list of rules, each with a `deprecated` and `suggestion` option.

`deprecated`           | A list of **regular expressions** which specify the classes deprecated by this rule.

`suggestion`           | A string to be included in the rule's error message. Make this informative and specific to the rule that it is contained in.

`addendum`             | A string to be included at the end of every error message of the rule set. (Optional)



### FinalNewline



Files must have a final newline. This results in better diffs when

adding lines to the file, since SCM systems such as git won't think that you

touched the last line.



You can customize whether or not a final newline exists with the `present`

option.



Example configuration:



```yaml

---

linters:

  FinalNewline:

    enabled: true

```



Linter-Specific Option | Description

-----------------------|---------------------------------------------------------

`present`              | Whether a final newline should be present (default **true**)



### ErbSafety



Runs the checks provided by

[better-html's erb safety test helper](https://github.com/Shopify/better-html#testing-for-valid-html-and-erb).



When using ERB interpolations in javascript contexts, this linter enforces the usage of safe helpers such as `.to_json`.

See [better-html's readme](https://github.com/Shopify/better-html#testing-for-valid-html-and-erb) for more information.



Any ERB statement that does not call a safe helper is deemed unsafe and a violation is shown.



For example:

```erb

Not allowed ❌

<a onclick="alert(<%= some_data %>)">



Allowed ✅

<a onclick="alert(<%= some_data.to_json %>)">

```



```erb

Not allowed ❌

<script>var myData = <%= some_data %>;



Allowed ✅

var myData = <%= some_data.to_json %>;

```



Example configuration:



```yaml

---

linters:

  ErbSafety:

    enabled: true

    better_html_config: .better-html.yml

```



Linter-Specific Option | Description

-----------------------|---------------------------------------------------------

`better_html_config`   | Name of the configuration file to use for `better-html`. Optional. Valid options and their defaults are described [in better-html's readme](https://github.com/Shopify/better-html#configuration).



### Rubocop



Runs RuboCop on all ruby statements found in ERB templates. The RuboCop configuration that `erb_lint` uses can inherit from

the configuration that the rest of your application uses. `erb_lint` can be configured independently however, as it will often

be necessary to disable specific RuboCop rules that do not apply to ERB files.



**Note**: Each ruby statement (between ERB tags `<% ... %>`) is parsed and analyzed independently of each other. Any rule that requires a broader context can trigger false positives (e.g. `Lint/UselessAssignment` will complaint for an assignment even if used in a subsequent ERB tag).



Example configuration:



```yaml

---

linters:

  Rubocop:

    enabled: true

    rubocop_config:

      inherit_from:

        - .rubocop.yml

      Layout/InitialIndentation:

        Enabled: false

      Layout/LineLength:

        Enabled: false

      Layout/TrailingEmptyLines:

        Enabled: false

      Layout/TrailingWhitespace:

        Enabled: false

      Naming/FileName:

        Enabled: false

      Style/FrozenStringLiteralComment:

        Enabled: false

      Lint/UselessAssignment:

        Enabled: false

      Rails/OutputSafety:

        Enabled: false

```



The cops disabled in the example configuration above provide a good starting point.



Linter-Specific Option | Description

-----------------------|---------------------------------------------------------

`rubocop_config`       | A valid rubocop configuration hash. Mandatory when this cop is enabled. See [rubocop's manual entry on Configuration](http://rubocop.readthedocs.io/en/latest/configuration/)

`only`                 | Only run cops listed in this array instead of all cops.

`config_file_path`     | A path to a valid rubocop configuration file. When this is provided, `rubocop_config` will be ignored.



### RequireInputAutocomplete

This linter prevents the usage of certain types of HTML `` without an `autocomplete` argument: `color`, `date`, `datetime-local`, `email`, `month`, `number`, `password`, `range`, `search`, `tel`, `text`, `time`, `url`, or `week`.

The HTML autocomplete helps users to complete filling in forms by using data stored in the browser. This is particularly useful for people with **motor disabilities** or **cognitive impairment** who may have difficulties filling out forms online.



```

Bad ❌



Good ✅



```



### RightTrim



Trimming at the right of an ERB tag can be done with either `=%>` or `-%>`, this linter enforces one of these two styles.



Example configuration:



```yaml

---

linters:

  RightTrim:

    enabled: true

    enforced_style: '-'

```



Linter-Specific Option | Description

-----------------------|---------------------------------------------------------

`enforced_style`       | Which style to enforce, can be either `-` or `=`. Optional. Defaults to `-`.



### SpaceAroundErbTag



Enforce a single space after `<%` and before `%>` in the ERB source.

This linter ignores opening ERB tags (`<%`) that are followed by a newline,

and closing ERB tags (`%>`) that are preceded by a newline.



```erb

Bad ❌

<%foo%>

<%=foo-%>



Good ✅

<% foo %>



<%

  foo

%>

```



Example configuration:



```yaml

---

linters:

  SpaceAroundErbTag:

    enabled: true

```



### NoJavascriptTagHelper



This linter prevents the usage of

Rails' [`javascript_tag`](https://apidock.com/rails/ActionView/Helpers/JavaScriptHelper/javascript_tag)

helper in ERB templates.



The html parser used in this gem knows not to look for html tags within certain other tags

like `script`, `style`, and others. The html parser does this to avoid confusing javascript

expressions like `if (11)` for a malformed html tag. Using the `javascript_tag` in

a ERB template prevents the parser from recognizing the change of parsing context and may

fail or produce erroneous output as a result.



```erb

Bad ❌

<%= javascript_tag(content, defer: true) %>

Good ✅

<%== content %>



Bad ❌

<%= javascript_tag do %>

  alert(1)

<% end %>

Good ✅



  alert(1)



```



The autocorrection rule adds `//` markers to the existing script, as this is the default

behavior for `javascript_tag`. This can be disabled by changing the `correction_style` linter option

from `cdata` to `plain`.



Example configuration:



```yaml

---

linters:

  NoJavascriptTagHelper:

    enabled: true

    correction_style: 'plain'

```



Linter-Specific Option | Description

-----------------------|---------------------------------------------------------

`correction_style`     | When configured with `cdata`, adds CDATA markers. When configured with `plain`, don't add makers. Defaults to `cdata`.



### RequireScriptNonce

This linter prevents the usage of HTML ``, Rails `javascript_tag`, `javascript_include_tag` and `javascript_pack_tag` without a `nonce` argument. The purpose of such a check is to ensure that when [content securty policy](https://edgeguides.rubyonrails.org/security.html#content-security-policy) is implemented in an application, there is a means of discovering tags that need to be updated with a `nonce` argument to enable script execution at application runtime.



```

Bad ❌

<script>

    alert(1)



Good ✅



    alert(1)



```



```

Bad ❌

<%= javascript_tag do -%>

  alert(1)

<% end -%>

Good ✅

<%= javascript_tag nonce: true do -%>

  alert(1)

<% end -%>

```



```

Bad ❌

<%= javascript_include_tag "script" %>

Good ✅

<%= javascript_include_tag "script", nonce: true %>

```



```

Bad ❌

<%= javascript_pack_tag "script" %>

Good ✅

<%= javascript_pack_tag "script", nonce: true %>

```



### SelfClosingTag



This linter enforces self closing tag styles for void elements.



The void elements are `area`, `base`, `br`, `col`, `embed`, `hr`, `img`, `input`, `keygen`, `link`, `menuitem`, `meta`, `param`, `source`, `track`, and `wbr`.



If `enforced_style` is set to `always` (XHTML style):



```erb

Bad ❌



Good ✅

Some Image

```



If `enforced_style` is set to `never` (HTML5 style):

```erb

Bad ❌



Good ✅



```



Example configuration:



```yaml

---

linters:

  SelfClosingTag:

    enabled: true

    enforced_style: 'always'

```



Linter-Specific Option | Description

-----------------------|---------------------------------------------------------

`enforced_style`       |  If we should `always` or `never` expect self closing tags for void elements. Defaults to `never`.



### AllowedScriptType



This linter prevent the addition of `` tags that have `type` attributes that are not in a white-list of allowed values.



It is common practice for web developers to use `<script>` tags with non-executable

`type` attributes, such as `application/json` or `text/html` to pass arbitrary data into an html page.

Despite not being executable, these tags are subject to the same parsing quirks as executable script tags, and

it is therefore more difficult to prevent security issues from creeping in. Consider for instance an application

where it is possible to inject the string `` unescaped into a `text/html` tag, the application

would be vulnerable to XSS.



This pattern can easily be replaced by `<div>` tags with `data` attributes that can just as easily be read

from javascript, and have the added benefit of being safer. When `content_tag(:div)` or `tag.div()` is used

to pass arbitrary user data into the html document, it becomes much harder to inadvertently introduce a

security issue.



It may also be desirable to avoid typos in `type` attributes.



```html

Bad ❌

<script type="text/javacsrïpt">

Good ✅



```



By default, this linter allows the `type` attribute to be omitted, as the behavior in browsers is to

consider `` to be the same as `<script type="text/javascript">`. When the linter is configured with

`allow_blank: false`, instances of `<script>` tags without a type will be auto-corrected

to `<script type="text/javascript">`.



It may also be desirable to disallow `<script>` tags from appearing anywhere in your application.

For instance, Rails applications can benefit from serving static javascript code from the asset

pipeline, as well as other security benefits.

The `disallow_inline_scripts: true` config option may be used for that purpose.



Example configuration:



```yaml

---

linters:

  AllowedScriptType:

    enabled: true

    allowed_types:

      - 'application/json'

      - 'text/javascript'

      - 'text/html'

    allow_blank: false

    disallow_inline_scripts: false

```



Linter-Specific Option    | Description

--------------------------|---------------------------------------------------------

`allowed_types`           | An array of allowed types. Defaults to `["text/javascript"]`.

`allow_blank`             | True or false, depending on whether or not the `type` attribute may be omitted entirely from a `<script>` tag. Defaults to `true`.

`disallow_inline_scripts` | Do not allow inline `<script>` tags anywhere in ERB templates. Defaults to `false`.



### HardCodedString



`HardCodedString` warns if there is a visible hardcoded string in the DOM. It does not check for a hardcoded string nested inside a JavaScript tag.



Example configuration:



```yaml

---

linters:

  HardCodedString:

    enabled: true

    corrector:

      path: path/to/corrector_file.rb

      name: I18nCorrector

      i18n_load_path: config/locales/en.yml

```



To leverage this linter's autocorrect feature, you must define the configuration for its `corrector`, such that its path, class name, and `i18n_load_path` are resolvable.



Linter-Specific Option    | Description

--------------------------|---------------------------------------------------------

path | a string pointing to the path to the corrector file

name | the name of the corrector class (can [either be `I18nCorrector` or `Rubocop::I18nCorrector`](https://github.com/Shopify/erb-lint/blob/19c9ddb94f0ea1d73ac12e18a7ea822d76adeeab/lib/erb_lint/linters/hard_coded_string.rb#L17))

i18n_load_path | a string pointing to the path of the file(s) to be translated



Below is an example corrector file. For your project, the actual details of the `autocorrect` method are left up to how you want to correct those offenses.



```ruby

class I18nCorrector

  attr_reader :node



  def initialize(node, filename, i18n_load_path, range)

  end



  def autocorrect(tag_start:, tag_end:)

    ->(corrector) do

      node

    end

  end

end

```



## CommentSyntax



This linter enforces the use of the correct ERB comment syntax, since Ruby comments (`<% # comment %>` with a space) are not technically valid ERB comments.



```erb

Bad ❌

<% # This is a Ruby comment %>

Good ✅

<%# This is an ERB comment %>



Bad ❌

<% # This is a Ruby comment; it can fail to parse. %>

Good ✅

<%# This is an ERB comment; it is parsed correctly. %>



Good ✅

<%

  # This is a multi-line ERB comment.

%>

```



## Custom Linters



`erb_lint` allows you to create custom linters specific to your project. It will load linters from the `.erb_linters` directory in the root of your

repository. See the [linters directory](lib/erb_lint/linters) for examples of how to write linters.



```ruby

# .erb_linters/custom_linter.rb



module ERBLint

  module Linters

    class CustomLinter < Linter

      include LinterRegistry



      class ConfigSchema < LinterConfig

        property :custom_message, accepts: String

      end

      self.config_schema = ConfigSchema



      def run(processed_source)

        unless processed_source.file_content.include?('this file is fine')

          add_offense(

            processed_source.to_source_range(0 ... processed_source.file_content.size),

            "This file isn't fine. #{@config.custom_message}"

          )

        end

      end

    end

  end

end

```



By default, this linter would be disabled. You can enable it by adding an entry to `.erb_lint.yml`:



```yaml

---

linters:

  CustomLinter:

    enabled: true

    custom_message: We suggest you change this file.

```



Test your linter by running `erb_lint`'s command-line interface:



```bash

bundle exec erb_lint --enable-linters custom_linter --lint-all

```



Running this on a random project might yield this output:



```

Linting 15 files with 1 linters...



This file isn't fine. We suggest you change this file.

In file: app/views/layouts/application.html.erb:1



Errors were found in ERB files

```



To write a linter that can autocorrect offenses it detects, simply add an

`autocorrect` method that returns a callable. The callable is called with an instance of

[`RuboCop::Cop::Corrector`](http://www.rubydoc.info/github/bbatsov/RuboCop/RuboCop/Cop/Corrector)

as argument, and therefore erb_lint correctors work exactly as RuboCop correctors do.



```ruby

def autocorrect(_processed_source, offense)

  lambda do |corrector|

    corrector.insert_after(offense.source_range, "this file is fine")

  end

end

```



## Output formats



You can change the output format of ERB Lint by specifying formatters with the `-f/--format` option.



### Multiline (default)



```sh

$ erb_lint

Linting 8 files with 12 linters...



Remove multiple trailing newline at the end of the file.

In file: app/views/users/show.html.erb:95



Remove newline before `%>` to match start of tag.

In file: app/views/subscriptions/index.html.erb:38



2 error(s) were found in ERB files

```



### Compact



```sh

erb_lint --format compact

Linting 8 files with 12 linters...

app/views/users/show.html.erb:95:0: Remove multiple trailing newline at the end of the file.

app/views/users/_graph.html.erb:27:37: Extra space detected where there should be no space

2 error(s) were found in ERB files

```



### JUnit



```sh

erb_lint --format junit

<?xml version="1.0" encoding="UTF-8"?>

<testsuite name="erb_lint" tests="2" failures="2">

  <properties>

    <property name="erb_lint_version" value="%{erb_lint_version}"/>

    <property name="ruby_engine" value="%{ruby_engine}"/>

    <property name="ruby_version" value="%{ruby_version}"/>

    <property name="ruby_patchlevel" value="%{ruby_patchlevel}"/>

    <property name="ruby_platform" value="%{ruby_platform}"/>

  </properties>

  <testcase name="app/views/subscriptions/_loader.html.erb" file="app/views/subscriptions/_loader.html.erb" lineno="1">

    <failure message="SpaceInHtmlTag: Extra space detected where there should be no space." type="SpaceInHtmlTag">

      <![CDATA[SpaceInHtmlTag: Extra space detected where there should be no space. at app/views/subscriptions/_loader.html.erb:1:7]]>

    </failure>

  </testcase>

  <testcase name="app/views/application/index.html.erb" file="app/views/subscriptions/_menu.html.erb"/>

</testsuite>

```



### GitLab



Used by [GitLab Code

Quality](https://docs.gitlab.com/ee/ci/testing/code_quality.html#implement-a-custom-tool).



```json

[

   {

      "description":"Extra space detected where there should be no space.",

      "check_name":"SpaceInHtmlTag",

      "fingerprint":"5a259c7cafa2c9ca229dfd7d21536698",

      "severity":"info",

      "location":{

         "path":"app/views/subscriptions/_loader.html.erb",

         "lines":{

            "begin":1,

            "end":1

         }

      }

   },

   {

      "description":"Remove newline before `%\u003e` to match start of tag.",

      "check_name":"ClosingErbTagIndent",

      "fingerprint":"60b4ed2120c7abeebebb43fba4a19559",

      "severity":"warning",

      "location":{

         "path":"app/views/subscriptions/_loader.html.erb",

         "lines":{

            "begin":52,

            "end":54

         }

      }

   }

]

```



## Caching



The cache is currently opt-in - to turn it on, use the `--cache` option:



```sh

erb_lint --cache ./app

Cache mode is on

Linting 413 files with 15 linters...

File names pruned from the cache will be logged



No errors were found in ERB files

```



Cached lint results are stored in the `.erb_lint_cache` directory by default, though a custom directory can be provided

via the `--cache-dir` option. Cache filenames are computed with a hash of information about the file and `erb_lint` settings.

These files store instance attributes of the `CachedOffense` object, which only contain the `Offense` attributes

necessary to restore the results of running `erb_lint` for output. The cache also automatically prunes outdated files each time it's run.



You can also use the `--clear-cache` option to delete the cache file directory.



## License



This project is released under the [MIT license](LICENSE.txt).