HHVM 4.40 is released! This release marks the end of support for 4.33; hhvm 4.34–4.39 remain supported, as do the 4.8 and 4.32 LTS releases.

Breaking Changes

• specifying the same XHP attribute twice (<foo x="1" x="2" />) is now a syntax error

Future Changes

A change last year unintentionally made the parser accept arbitrary types for XHP children declarations, however:

• this remains unsupported by the XHP class library.
• the typechecker does not validate children.
• this can lead to impossible-to-satisfy children declarations, such as references to undefined types.

We are changing the typechecker to verify that XHP children declarations do not refer to undefined types; in the context of XHP children declarations, the following types will be considered valid by the typechecker:

• the case-sensitive special values pcdata, any, or empty.
• XHP category names, such as %foo.
• a defined, non-aliased, non-generic Hack type, such as a class name, XHP classname, or interface.

We expect this change to be included in 4.41.

There are some additional things to be aware of:

• only the declaration is validated; the typechecker will not verify that provided children actually match the declaration. This will remain a runtime-only check, which must be supported by the XHP class library.
• there are no typechecker checks for XHP categories in children declarations.
• types other than XHP class names - such as standard classes or interfaces - may not be fully supported by the XHP class library.
• type aliases are not permitted.

Additionally, this release includes disabled support for xhp class foo {} as an alternative syntax to class :foo {}; this is to unblock future work on improving interactions between XHP and namespaces - usage is not recommended at this time.