Inconsistent PHPDoc and type definitions across Yii2 (for example `BaseYii::$app`).

[terabytesoftw]

Several Yii2 classes contain inconsistent or incomplete PHPDoc annotations that affect static analysis (PHPStan/Psalm) and IDE inference.

A representative example is found in BaseYii.php:

/**
 * @var \yii\console\Application|\yii\web\Application the application instance
 *
 * @phpstan-var \yii\console\Application|\yii\web\Application<TUserIdentity>
 * @psalm-var \yii\console\Application|\yii\web\Application<TUserIdentity>
 */
public static $app;

However, in many parts of the framework, $app can be null (for example, during test teardown or before bootstrap), leading to PHPStan errors like:

Property Yii::$app (yii\web\Application|yii\console\Application) does not accept null.

This specific case also appears in:

tests/TestCase.php
tests/framework/console/controllers/DbMessageControllerTest.php
tests/framework/i18n/DbMessageSourceTest.php

The same pattern occurs elsewhere: properties and return types that are dynamically nullable or polymorphic, but their PHPDoc types don’t reflect that.

A review of the phpstan-baseline.neon file shows multiple suppressions related to:

null assignments to properties without null
mixed or union type mismatches

This indicates a systemic documentation/type inconsistency between runtime behavior and declared PHPDoc types.

[mspirkov]

Yes, many of these issues have been fixed, but many still remain. I plan to fix some of them when updating PHPStan level to 4.

[mspirkov]

It would also be great to include tests in the analysis, but I don't have enough time to fix all the errors yet, as there are many of them.

[terabytesoftw]

It would also be great to include tests in the analysis, but I don't have enough time to fix all the errors yet, as there are many of them.

Once we fix the PHPDoc inconsistencies, then I'll fix the static analysis in the tests.