Syntax tweaks

[nikic]

RFC: https://wiki.php.net/rfc/variable_syntax_tweaks

This is a collection of minor syntactic extensions that cover holes left by the original uniform variable syntax RFC:

• "foo$bar" is now treated the same ways as "foobar", e.g. you can write "foo$bar"[0].
• Magic constants are treated the same as normal constants, e.g. __FUNCTION__[0] becomes legal.
• Class constants become fully dereferencable, in particular Foo::CLASS_NAME::$bar becomes legal.
• new (expr) is now accepted. Previously it was not possible to use arbitrary expressions with new.
• Similarly $var instanceof (expr) is now accepted.

These are all edge cases, but things I've received complaints about over the years.

[nikic]

One thing I'm unsure about here is the instanceof syntax. It could also conceivably be $foo instanceof (expr).

Ideally we'd allow $foo instanceof expr, but that doesn't work because of the constant vs class name conflict. We could resolve it by parsing the RHS as a constant and then performing a class bit of fixup to convert a top-level constant access to a class name reference, but I'm afraid that doing this will cause problems in the future, once we add support for generics.