XHPAST currently can not parse $x = yield $y;. I suspect this was added to the PHP grammar after XHPAST diverged. I'm hopeful the fix is straightforward.

The full yield syntax is a bit zany:

$data = (yield $key => $value);

This is entangled with T9753.

• macOS ships with Bison 2.3.
• Under Bison 3, with -Wall, the grammar for Bison 2.3 emits a bunch of warnings. The -Wall flag was added in D13970 and the warnings were fixed in D13974.

These Bison 3 fixes are not backward-compatible. Since the only goal of those changes was to improve tidiness, I'm just going to revert them. I think building more easily on macOS is generally a more important goal than building more cleanly on Bison 3.

A future change could do version detection, or require Bison 3 (if this serves some other goal) and version-detect that Bison is too old.

In T13492#251814, @epriestley wrote:

XHPAST currently can not parse $x = yield $y;.

A complication here is that PHP can't either, until PHP7. In PHP 5.5, only $x = (yield $y); is valid.

So this change is somewhat moot. Once xhpast can parse this construction, the linter needs to emit a message forbidding it.

See also T13588. Using static::class to work around changes to the scope of static in PHP 8.1 is also possible now that PHP 5.5 is the minimum version, and some uses of get_class($this) might be replaceable. There's no strong motivator for this, it's just a little cleaner.