erb-lint is a tool to help lint your ERB or HTML files using the included linters or by writing your own.
- 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.
gem install erb_lint...or add the following to your Gemfile and run bundle install:
gem 'erb_lint', require: falseCreate a .erb-lint.yml file in your project, with the following structure:
---
EnableDefaultLinters: true
linters:
ErbSafety:
enabled: true
better_html_config: .better-html.yml
Rubocop:
enabled: true
rubocop_config:
inherit_from:
- .rubocop.ymlSee below for linter-specific configuration options.
This gem provides a command-line interface which can be run like so:
- Run
erblint [options]if the gem is installed standalone. - Run
bundle exec erblint [options]if the gem is installed as a Gemfile dependency for your app.
For example, erblint --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 that is used, you can configure it by adding it to your config file as follows:
---
glob: "**/*.{html,text,js}{+*,}.erb"
linters:
ErbSafety:
enabled: true
better_html_config: .better-html.yml
Rubocop:
enabled: true
rubocop_config:
inherit_from:
- .rubocop.ymlEnableDefaultLinters: enables or disables default linters. Default linters are enabled by default.
| Available Linters | Default | Description |
|---|---|---|
| AllowedScriptType | Yes | prevents the addition of <script> tags that have type attributes that are not in a white-list of allowed values |
| ClosingErbTagIndent | Yes | |
| ExtraNewline | Yes | |
| FinalNewline | Yes | warns about missing newline at the end of a ERB template |
| NoJavascriptTagHelper | Yes | prevents the usage of Rails' javascript_tag |
| ParserErrors | Yes | |
| RightTrim | Yes | enforces trimming at the right of an ERB tag |
| SelfClosingTag | Yes | enforces self closing tag styles for void elements |
| SpaceAroundErbTag | Yes | enforces a single space after <% and before %> |
| SpaceIndentation | Yes | |
| SpaceInHtmlTag | Yes | |
| TrailingWhitespace | Yes | |
| DeprecatedClasses | No | warns about deprecated css classes |
| ErbSafety | No | detects unsafe interpolation of ruby data into various javascript contexts and enforce usage of safe helpers like .to_json. |
| Rubocop | No | runs RuboCop rules on ruby statements found in ERB templates |
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:
---
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) |
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:
---
linters:
FinalNewline:
enabled: true| Linter-Specific Option | Description |
|---|---|
present |
Whether a final newline should be present (default true) |
Runs the checks provided by better-html's erb safety test helper.
When using ERB interpolations in javascript contexts, this linter enforces the usage of safe helpers such as .to_json.
See better-html's readme for more information.
Any ERB statement that does not call a safe helper is deemed unsafe and a violation is shown.
For example:
Not allowed ❌
<a onclick="alert(<%= some_data %>)">
Allowed ✅
<a onclick="alert(<%= some_data.to_json %>)">Not allowed ❌
<script>var myData = <%= some_data %>;</script>
Allowed ✅
<script>var myData = <%= some_data.to_json %>;</script>Example configuration:
---
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. |
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:
---
linters:
Rubocop:
enabled: true
rubocop_config:
inherit_from:
- .rubocop.yml
Layout/InitialIndentation:
Enabled: false
Layout/TrailingEmptyLines:
Enabled: false
Layout/TrailingWhitespace:
Enabled: false
Naming/FileName:
Enabled: false
Style/FrozenStringLiteralComment:
Enabled: false
Metrics/LineLength:
Enabled: false
Lint/UselessAssignment:
Enabled: false
Rails/OutputSafety:
Enabled: falseThe 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 |
only |
Only run cops listed in this array instead of all cops. |
Trimming at the right of an ERB tag can be done with either =%> or -%>, this linter enforces one of these two styles.
Example configuration:
---
linters:
RightTrim:
enabled: true
enforced_style: '-'| Linter-Specific Option | Description |
|---|---|
enforced_style |
Which style to enforce, can be either - or =. Optional. Defaults to -. |
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.
Bad ❌
<%foo%>
<%=foo-%>
Good ✅
<% foo %>
<%
foo
%>Example configuration:
---
linters:
SpaceAroundErbTag:
enabled: trueThis linter prevents the usage of
Rails' 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.
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:
---
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. |
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):
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):
Bad ❌
<hr />
Good ✅
<meta charset="UTF-8">Example configuration:
---
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. |
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.
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:
---
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. |
disallow_inline_scripts |
Do not allow inline <script> tags anywhere in ERB templates. Defaults to false. |
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 for examples of how to write linters.
# .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 offenses(processed_source)
errors = []
unless processed_source.file_content.include?('this file is fine')
errors << Offense.new(
self,
processed_source.to_source_range(0 ... processed_source.file_content.size),
"This file isn't fine. #{@config.custom_message}"
)
end
errors
end
end
end
endBy default, this linter would be disabled. You can enable it by adding an entry to .erb-lint.yml:
---
linters:
CustomLinter:
enabled: true
custom_message: We suggest you change this file.Test your linter by running erblint's command-line interface:
bundle exec erblint --enable-linters custom_linter --lint-allRunning 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
as argument, and therefore erb-lint correctors work exactly as RuboCop correctors do.
def autocorrect(_processed_source, offense)
lambda do |corrector|
corrector.insert_after(offense.source_range, "this file is fine")
end
endYou can change the output format of ERB Lint by specifying formatters with the -f/--format option.
$ erblint
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 fileserblint --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 filesThis project is released under the MIT license.