j2lint

Jinja2-Linter

AVD Ecosystem - Jinja2 Linter

Project Goals

Build a Jinja2 linter that will provide the following capabilities:

• Validate syntax according to AVD style guide.
• Capability to run as part of a CI pipeline to enforce j2lint rules.
• Develop an extension that works with VSCode and potentially other IDEs i.e PyCharm.

Syntax and code style issues

Code	Short Description	Description
S0	jinja-syntax-error	Jinja2 syntax should be correct
S1	single-space-decorator	A single space should be added between Jinja2 curly brackets and a variable's name
S2	operator-enclosed-by-spaces	When variables are used in combination with an operator, the operator shall be enclosed by space
S3	jinja-statements-indentation	Nested jinja code block should follow next rules: - All J2 statements must be enclosed by 1 space - All J2 statements must be indented by 4 more spaces within jinja delimiter - To close a control, end tag must have same indentation level
S4	jinja-statements-single-space	Jinja statement should have at least a single space after '{%' and a single space before '%}'
S5	jinja-statements-no-tabs	Indentation should not use tabulation but 4 spaces
S6	jinja-statements-delimiter	Jinja statements should not have {%- or {%+ or -%} as delimiters
S7	single-statement-per-line	Jinja statements should be on separate lines
V1	jinja-variable-lower-case	All variables should use lower case
V2	jinja-variable-format	If variable is multi-words, underscore _ should be used as a separator

Getting Started

Requirements

Python version 3.8+

Install with pip

To get started, you can use Python pip to install j2lint:

Install the latest stable version:

pip3 install j2lint

Install the latest development version:

pip3 install git+https://github.com/aristanetworks/j2lint.git

Running the linter

j2lint <path-to-directory-of-templates>

Running the linter on a specific file

j2lint <path-to-directory-of-templates>/template.j2

Listing linting rules

j2lint --list

Running the linter with verbose linter error output

j2lint <path-to-directory-of-templates> --verbose

Running the linter with logs enabled. Logs saved in jinja2-linter.log in the current directory

j2lint <path-to-directory-of-templates> --log

To enable debug logs, use both options:

j2lint <path-to-directory-of-templates> --log --debug

Running the linter with JSON format for linter error output

j2lint <path-to-directory-of-templates> --json

Ignoring rules

1. The --ignore option can have one or more of these values: syntax-error, single-space-decorator, filter-enclosed-by-spaces, jinja-statement-single-space, jinja-statements-indentation, no-tabs, single-statement-per-line, jinja-delimiter, jinja-variable-lower-case, jinja-variable-format.

2. If multiple rules are to be ignored, use the --ignore option along with rule descriptions separated by space.

   j2lint <path-to-directory-of-templates> --ignore <rule_description1> <rule_desc>
   

Note This runs the custom linting rules in addition to the default linting rules. When using the -i/--ignore or -w/--warn options, the arguments MUST either:

• Be entered at the end of the CLI as in the example above
• Be entered as the last options before the <path-to-directory-of-templates> with -- separator. e.g.

  j2lint --ignore <rule_description1> <rule_desc> -- <path-to-directory-of-templates>
  

1. If one or more linting rules are to be ignored only for a specific jinja template file, add a Jinja comment at the top of the file. The rule can be disabled using the short description of the rule or the id of the rule.

   {# j2lint: disable=S6}
   
   # OR
   {# j2lint: disable=jinja-delimiter #}
   

2. Disabling multiple rules

   {# j2lint: disable=jinja-delimiter j2lint: disable=S1 #}
   

Adding custom rules

1. Create a new rules directory under j2lint folder.

2. Add custom rule classes which are similar to classes in j2lint/rules directory: The file name of rules should be in snake_case and the class name should be the PascalCase version of the file name. For example:

   • File name: jinja_operator_has_spaces_rule.py
   • Class name: JinjaOperatorHasSpacesRule

3. Run the jinja2 linter using --rules-dir option

   j2lint <path-to-directory-of-templates> --rules-dir <custom-rules-directory>
   

Note This runs the custom linting rules in addition to the default linting rules.

Running jinja2 linter help command

j2lint --help

Running jinja2 linter on STDIN template. This option can be used with VS Code.

j2lint --stdin

Using j2lint as a pre-commit-hook

1. Add j2lint pre-commit hook inside your repository in .pre-commit-config.yaml.

   - repo: https://github.com/aristanetworks/j2lint.git
       rev: <release_tag/sha>
       hooks:
       - id: j2lint
   

2. Run pre-commit -> pre-commit run --all-files

Note When using -i/--ignore or -w/--warn argument in pre-commit, use the following syntax

- repo: https://github.com/aristanetworks/j2lint.git
    rev: <release_tag/sha>
    hooks:
    - id: j2lint
    # Using -- to separate the end of ignore from the positional arguments
    # passed to j2lint
      args: [--ignore, S3, jinja-statements-single-space, --]

Acknowledgments

This project is based on salt-lint and jinjalint