Nested templates regression since 5.3

[vudaltsov]

Here's what Psalm v5.2 correctly reports for https://psalm.dev/r/af716b51e1:

ERROR: InvalidReturnType - .stuff/test.php:37:44 - The declared return type 'int' for IntValueProcessor::process is incorrect, got '''' (see https://psalm.dev/011)
    public function process(Value $value): mixed


ERROR: InvalidReturnStatement - .stuff/test.php:39:16 - The inferred type '''' does not match the declared return type 'int' for IntValueProcessor::process (see https://psalm.dev/128)
        return '';

Psalm v5.3 reports No issues!

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/af716b51e1

<?php

declare(strict_types=1);

/**
 * @template T
 */
interface Value
{
}

/**
 * @implements Value<int>
 */
final class IntValue implements Value
{
}

/**
 * @template T
 * @template TValue of Value<T>
 */
interface ValueProcessor
{
    /**
     * @param TValue $value
     * @return T
     */
    public function process(Value $value): mixed;
}

/**
 * @implements ValueProcessor<int, IntValue>
 */
final class IntValueProcessor implements ValueProcessor
{
    public function process(Value $value): mixed
    {
        return '';
    }
}

Psalm output (using commit 4eacb2f):

No issues!

[vudaltsov]

Interestingly the problem disappears if I remove : mixed return type in IntValueProcessor::process.

https://psalm.dev/r/1a20f5a3a4

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/1a20f5a3a4

<?php

declare(strict_types=1);

/**
 * @template T
 */
interface Value
{
}

/**
 * @implements Value<int>
 */
final class IntValue implements Value
{
}

/**
 * @template T
 * @template TValue of Value<T>
 */
interface ValueProcessor
{
    /**
     * @param TValue $value
     * @return T
     */
    public function process(Value $value): mixed;
}

/**
 * @implements ValueProcessor<int, IntValue>
 */
final class IntValueProcessor implements ValueProcessor
{
    public function process(Value $value)
    {
        return '';
    }
}

Psalm output (using commit 4eacb2f):

ERROR: InvalidReturnStatement - 39:16 - The inferred type '''' does not match the declared return type 'int' for IntValueProcessor::process

ERROR: InvalidReturnType - 37:21 - The declared return type 'int' for IntValueProcessor::process is incorrect, got ''''

[vudaltsov]

Regression occurred after #8926 was merged.

Commit da001c4 is the last one, when Psalm reports the problem (correct behavior).

[vudaltsov]

Closing in favor of #9245 which has a simpler example.