Coding Guidelines

More information is found in the Coding Guidelines section of the "TYPO3 Explained" manual (formerly known as "Core API").

This is just a very brief overview.

PHP

Make sure you are using the correct PHP code style. It is based on the TYPO3 Coding Standards, (which follows PER-CS1.0 / PSR-12 and transition into PER-CS2.0 at the time of this writing), and covered in the TYPO3 Coding Guidelines.

See PhpStorm setup: CGL for information on how to configure the correct coding style.

The Appendix contains information on scripts to check / fix coding guideline issues: CGL check and fix

Most PHP coding guidelines can be automatically applied with the command:

Build/Scripts/runTests.sh -s cgl

JavaScript

The following rules should be applied for JavaScript: Airbnb JavaScript Style Guide

TypeScript

The following rules should be applied for TypeScript: Excel Micro TypeScript Style Guide.

Xliff files

Language files are usually stored in a Folder Resources/Private/Language in files with the ending .xlf. Xliff files are indented using 2 spaces. The following command normalizes your XLIFF files:

Build/Scripts/runTests.sh -s normalizeXliff

Please also check Xliff / language files for Xliff-specific things to pay attention to.

XLIFF file naming

XLIFF files have historically been named with file names starting with locallang_. Newly introduced XLIFF files should drop the locallang_ prefix and only be named according to their purpose, for example clipboard.xlf or db/tt_content.xlf. Newly introduced file names should use snake_case.

TCA-related XLIFF files should either be called db.xlf or be stored in a folder named db, for example db/tt_content.xlf.

Label reference naming

Newly introduced label references should use snake case. Different parts of a label reference can be separated by dots, for example:

<trans-unit id="my_field.title">
    <source>My title</source>
</trans-unit>
<trans-unit id="my_field.description">
    <source>My description</source>
</trans-unit>

Existing labels should not be mass-changed to snake case, as each changed label must be retranslated into all languages.

Utilizing "translation domain syntax"

With Feature: #93334 - Translation Domain Mapping and Feature: #107759 - TranslateViewHelper supports translation domain syntax the label localization within Fluid template files and PHP code can be shortened:

<f:translate key="form.legend" domain="core.messages" />
<f:translate key="module.title" domain="core.module" />

$languageService->sL('backend.toolbar:save');

This syntax is preferred and should be utilized for any new code committed to TYPO3 v14+ because of these reasons:

It is shorter, easier to read, has no odd LLL:EXT: magic notation
Applies conventions of Symfony translation usage in other frameworks
Allows better automatic extraction and analysis (CLI commands)
Allows for better deprecations and usage analysis

Detailed reasons are found in the mentioned changelogs.