# 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
```

> [!TIP]
> Creating an `.erb_lint.yml` config file is _not_ mandatory; **the tool works out of the box with default settings**.
> 
>  Please note that the two config files referenced in the examples above and below _must_ exist, or you will get an error. (Of course, you can omit the two config file references (i.e. the `better_html_config` key, and the `rubocop_config` section.)

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
<hr /> <%# 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 `<script>` 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      |             |
| [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`. |
| [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)            |
| PartialInstanceVariable                          | No       | detects instance variables in partials |
| [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 |
| [StrictLocals](#strictlocals)                    | No       | enforces the use of strict locals in Rails view partial templates |

### 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 %>;</script>

Allowed ✅
<script>var myData = <%= some_data.to_json %>;</script>
```

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 `<input>` 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 ❌
<input type="email" ...>
Good ✅
<input type="email" autocomplete="nope" ...>
<input type="email" autocomplete="email" ...>
```

### 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 (1<a || b>1)` 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 ✅
<script defer="true"><%== content %></script>

Bad ❌
<%= javascript_tag do %>
  alert(1)
<% end %>
Good ✅
<script>
  alert(1)
</script>
```

The autocorrection rule adds `//<![CDATA[` and `//]]>` 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 `<script>`, 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)
</script>
Good ✅
<script nonce="<%= request.content_security_policy_nonce %>" >
    alert(1)
</script>
```

```
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 ❌
<link rel="stylesheet" type="text/css" href="styles.css">
Good ✅
<img src="someimage.png" alt="Some Image" />
```

If `enforced_style` is set to `never` (HTML5 style):
```erb
Bad ❌
<hr />
Good ✅
<meta charset="UTF-8">
```

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 `<script>` 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 `</script><script>` 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"></script>
Good ✅
<script type="text/javascript"></script>
```

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

### StrictLocals
This linter enforces the use of [strict locals](https://guides.rubyonrails.org/layouts_and_rendering.html#strict-locals) in Rails view partial templates.

```
# app/views/foo/_bar.html.erb

Bad ❌
<div>
  My name is <%= @name %>
</div>

Good ✅
<%# locals: (name:) %>
<div>
  My name is <%= name %>
</div>
```

**Note**: This linter does not enforce the use of strict locals in view templates (files that don't start with `_`).  
**Note**: This linter does not prevent the use of instance variables. It merely enforces that a strict locals declaration is present. It's recommended to use this linter in conjunction with the `PartialInstanceVariable` linter to enforce the use of locals.

## 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).