declare statement is not scoped when using curly braces

Description

When writing tests for phpcs sniff using some useful helpers regarding declare statements, I came up with an unusual behavior of the declare statements, when braces are used.

I was testing out a code that looked like this:

<?php
declare(strict_types=1)
echo 'hi!';

{
// Code.
}

that threw a fatal error because you cannot use curly braces with strict_types directive or alternative control structure syntax (declare: ... enddeclare;)

So I tried to see what will happen if I use a directive that allows the use of curly braces, like encoding. So I tried:

<?php

declare(encoding='ISO-8859-15')
echo 'aäaß' . "\n";

{
echo 'aäaß' . "\n";

}

And I got out:

aÀaÃ
aÀaÃ

I thought I'd get a parse error like when you omit the : when using if with endif; statement. Although, when testing the if statement with the curly braces, like in the example above, I can also see the echoed value before the condition, so I guess that's kinda expected.

What was a buggy behavior was this:

<?php

declare(encoding='ISO-8859-15') {
    echo 'aäaß' . "\n";
}

echo 'aäaß' . "\n";

I expected to see

aÀaÃ
aäaß

But I got (again)

aÀaÃ
aÀaÃ

So it seems that the declare statement, no matter if we are using curly braces, or alternative control structure syntax, will be applied throughout the file, instead of being scoped.

PHP Version

PHP 7.4.26

Operating System

Ubuntu 20.04 (on WSL)

El issue no indica ningún archivo fuente ni punto de entrada de pruebas. Empieza reproduciendo los ejemplos de PHP 7.4.26 que involucran declare(encoding=...) y llaves, y luego sigue el manejo de declare en el intérprete de PHP. Se considera terminado cuando la directiva está limitada a la sentencia entre llaves y el comportamiento observado está cubierto por una prueba de regresión.