[New Rule] Add declare(strict_types=1) to your PHP files

[lenaorobei]

Rule

All new PHP files MUST have strict type mode enabled by starting with declare(strict_types=1);. All updated PHP files SHOULD have strict type mode enabled. PHP interfaces SHOULD NOT have this declaration.

Reason

Source: Magento Technical Guidelines.

With PHP 7, it is possible to add type hinting to your code. However, this doesn't mean that types are actually enforced, unless strict typing is enabled by adding declare(strict_types=1) to the top of each PHP file.

PHP code becomes more robust when type hinting (argument types, return types) are added. With the declare(strict_types=1) added, there is less chance for bugs that related to type casting.

Implementation

Please refer to ExtDN an generic PHP CodeSniffer (not merged yet) implementations.

Important details

This sniff should be applicable to Magento >=2.2, because older versions of Magento supports PHP 5.5 and 5.6.
Follow the discussion about version specific sniffs for more details.

[larsroettig]

@lenaorobei I can implement this

[lenaorobei]

@larsroettig sounds good, but first we need to discuss the approach for version specific sniffs.

[buskamuza]

When implementing, please remove a static test that cover the same thing.

[lenaorobei]

As per architects discussion we need to determine how strict this rule should be:

• Applicable only to new files?
• Or only to changed files?
• How to check vendors extensions?

[sergeynezbritskiy]

There is a good sniff which checks that your code satisfies php7 styling code (type hints, return types, declaring strict type etc)
https://github.com/slevomat/coding-standard, can we reuse it ?

[tmotyl]

Any progress here? Is there help needed?

[lenaorobei]

@tmotyl
This coding standard is used to check older Magento 2.x versions that are compatible with PHP < 7.0. This is the reason why this rule is not beeng added here. We support only one version of coding standard, so there is no specific branches for separate Magento releases.

[markshust]

Since PHP 8 is now released, is it time to drop support for PHP < 7.0 and merge this in?

[guvra]

It looks like this can be closed. PHP version 8 has this feature enabled and does not require the extra line of code in each file.

This is not true.
You are probably thinking of this.
This has nothing to do with strict types.

[fredden]

This is not true.

Sorry, I was wrong. I've marked my comment as hidden to avoid confusion going forward. Thanks for calling this out.