Magic property is inferred as mixed after method call

[danog]

https://psalm.dev/r/10eec1df24

This really surprised me, because it looks like Psalm is automatically creating some mistaken assertion on the property assigned in the updateErrors method, because if the assignment is removed from updateErrors the error is fixed: https://psalm.dev/r/4e00eed4c5

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/10eec1df24

<?php

/**
 * @property array<string, string> $errors
 *
 * @psalm-seal-properties
 */
final class OrganizationObject {

	public function __get(string $key): mixed
	{
		return [];
	}

	public function __set(string $key, mixed $a): void
	{
	}

	public function updateErrors(): void {
		/** @var array<string, string> */
		$errors = [];
		$this->errors = $errors;
	}
	public function updateStatus(): void {
		$errors = $this->errors;
		/** @psalm-trace $errors */;
		$this->updateErrors();
		$errors = $this->errors;
		/** @psalm-trace $errors */;
	}
}

Psalm output (using commit 8f39de9):

INFO: Trace - 26:30 - $errors: array<string, string>

INFO: MixedAssignment - 28:3 - Unable to determine the type that $errors is being assigned to

INFO: Trace - 29:30 - $errors: mixed

INFO: UnusedVariable - 25:3 - $errors is never referenced or the value is not used

INFO: UnusedVariable - 28:3 - $errors is never referenced or the value is not used

https://psalm.dev/r/4e00eed4c5

<?php

/**
 * @property array<string, string> $errors
 *
 * @psalm-seal-properties
 */
final class OrganizationObject {

	public function __get(string $key): mixed
	{
		return [];
	}

	public function __set(string $key, mixed $a): void
	{
	}

	public function updateErrors(): void {
		/** @var array<string, string> */
		$errors = [];
		//$this->errors = $errors;
	}
	public function updateStatus(): void {
		$errors = $this->errors;
		/** @psalm-trace $errors */;
		$this->updateErrors();
		$errors = $this->errors;
		/** @psalm-trace $errors */;
	}
}

Psalm output (using commit 8f39de9):

INFO: UnusedVariable - 21:3 - $errors is never referenced or the value is not used

INFO: Trace - 26:30 - $errors: array<string, string>

INFO: Trace - 29:30 - $errors: array<string, string>

INFO: UnusedVariable - 25:3 - $errors is never referenced or the value is not used

INFO: UnusedVariable - 28:3 - $errors is never referenced or the value is not used