Keep track of delayed variance obligations and check them after
linking a class is otherwise finished. Obligations may either be
unresolved method compatibility (because the necessecary classes
aren't available yet) or open parent/interface dependencies. The
latter occur because we allow the use of not fully linked classes
as parents/interfaces now.
An important aspect of the implementation is we do not require
classes involved in variance checks to be fully linked in order for
the class to be fully linked. Because the involved types do have to
exist in the class table (as partially linked classes) and we do
check these for correct variance, we have the guarantee that either
those classes will successfully link lateron or generate an error,
but there is no way to actually use them until that point and as
such no possibility of violating the variance contract. This is
important because it ensures that a class declaration always either
errors or will produce an immediately usable class afterwards --
there are no cases where the finalization of the class declaration
has to be delayed until a later time, as earlier variants of this
patch did.
Because variance checks deal with classes in various stages of
linking, we need to use a special instanceof implementation that
supports this, and also introduce finer-grained flags that tell us
which parts have been linked already and which haven't.
Class autoloading for variance checks is delayed into a separate
stage after the class is otherwise linked and before delayed
variance obligations are processed. This separation is needed to
handle cases like A extends B extends C, where B is the autoload
root, but C is required to check variance. This could end up
loading C while the class structure of B is in an inconsistent
state.
We weren't able to do this in 7.1 because the deprecation notice
may be converted to an exception and __toString() can't throw,
which means that it ultimately become a fatal error. This issue
is resolved now, so we can mark the method as deprecated.
RFC: https://wiki.php.net/rfc/tostring_exceptions
And convert some object to string conversion related recoverable
fatal errors into Error exceptions.
Improve exception safety of internal code performing string
conversions.
Causes build failure on release+zts azure build. I'm rewriting this
code to separate the if/else handling, because they don't really
have anything in common anyway...
Even though we don't need it at runtime, add the BIND_IMPLICIT
flag to BIND_STATIC as well, so we can distinguish this case in
type inference.
This fixes a JIT miscompile in arrow_functions/002.phpt.
This is a minimal variance implementation: It does not support any
cyclic type dependencies. Additionally the preloading requirements
are much more restrictive than necessary. Hopefully we can relax
these in the future.
Fixes bug #76451, and more importantly lays necessary groundwork for
covariant/contravariant types. Bug #76451 is just an edge case, but
once covariance is introduced this will become a common problem instead.
Nikita Popov