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Introduce eslint on vue admin

This document represents an architecture decision record (ADR) and has been mirrored from the ADR section in our Shopware 6 repository. You can find the original version here

Context

We want to support ESLint of the administration vue app to keep and increase code quality.
By adding ESLint to the administration app, every developer will get instant feedback and best practices on his code by writing.

Decision

For the *.js linting, we want to get pretty close to a standard vue2 app linting. In the *.js linting chapter, we explain where and why we choose to leave the common way.
For the *.html.twig linting, we need to create a custom solution, which can handle or circumstance the twig syntax in our templates. We decided to convert all twig syntax to HTML comments within the linting process. This way, the linter ignores the twig parts and can handle the twig files like typical vue templates. The most significant tradeoff with this solution is that the linter cannot take the twig blocks into account on computing indentation levels.

*.js linting

For the *.js files we try to follow a standard vue cli linting way, with this adjustments:

*.spec.js linting

During writing unit test files, we do not want to get a max-len warning. A max-len rule may lead to hard understandable output in test names only to suit the max-len rules. In a test itself, you sometimes have selector phrases or something else where you exceed the max-len rule without a chance to solve it.

*.html.twig linting

Besides the twig-to-html-comment tradeoff, these exceptions are also made:
  • 'vue/component-name-in-template-casing': ['error', 'kebab-case'] - write vue component names in kebab-case in templates
  • 'vue/no-multiple-template-root': 'off', - due to external template files and component inheritance
  • 'vue/attribute-hyphenation': 'error' - write hello-word="" attributes instead of helloWorld=""
  • 'vue/no-parsing-error': ['error', {'nested-comment': false}] - ignore nested html comments, which may be a result of the twig-to-html-comment workflow
  • 'vue/valid-template-root': 'off' - @see vue/no-multiple-template-root
  • 'vue/valid-v-slot': ['error', { allowModifiers: true }] - allow .s in template slot names
  • 'vue/no-unused-vars': 'off' - the twig parser cannot understand if a scoped slot value is used or not used properly
  • 'vue/no-template-shadow': 'off' - for providing scoped values into another template scope
  • 'vue/no-lone-template': 'off' - in some composition cases lone template tags are used
  • 'vue/no-v-html': 'off' - for i18n and other reasons v-html is often used

twig block indentation

To accomplish the twig syntax being able to be linted, we needed to create a custom eslint-twig-vue-plugin and to accept the following changes in template writing:
before
<div>
<div data-gb-custom-block data-tag="block"></div>
<div>
now
<div>
<div data-gb-custom-block data-tag="block"></div>
<div>
To be able to lint the twig templates, we replace the twig syntax with HTML comments during the lint process, and thus every twig syntax is treated as an HTML comment and not recognised for indentation.

self-closing components

before
<sw-language-switcher></sw-language-switcher>
now
<sw-language-switcher />

attribute alignment

As soon as more than 1 attribute exists, every attribute gets its own line:
before
<div v-for="strategy in strategies" class="sw-app-app-url-changed-modal__content-choices">
<sw-icon small color="#189eff" name="default-basic-shape-circle-filled"></sw-icon>
now
<div
v-for="strategy in strategies"
class="sw-app-app-url-changed-modal__content-choices"
>
<sw-icon
small
color="#189eff"
name="default-basic-shape-circle-filled"
/>

Linting Pitfalls

invalid-x-end-tag

If you stumble upon a very red marked file from your linter, please check first that your twig syntax follows this pattern:
<div data-gb-custom-block data-tag="block"></div><!-- whitespace after and before twig syntax `{% ` and ` %}`. -->
<div data-gb-custom-block data-tag="block"></div><!-- missing whitespace after or before twig syntax `{%` or `%}` -->

disabling eslint rules in templates

It is possible to disable a specific linting rule in the template by using this syntax:
<!-- eslint-disable vue/eslint-rule-to-be-disabled -->
<div>
Please follow the know the rules, break the rules approach and not the dont bug me linter approach.

ESLint IDE setup

The *.js linting should run out of the box with PHPStorm or VSCode. For *.html.twig linting have a look at the next chapter.
ESLint is part of the CI pipeline, so a running ESLint environment is mandatory.

Twig Linting Setup

VSCode

Should work out of the box @see .vscode/settings.json.

PHPStorm

Add html,twig to eslint.additional.file.extensions list in Registry (Help > Find Action..., type registry... to locate it) and re-start the IDE.