The environment settings object is effectively the context a piece of
script is running under, for example, it contains the origin,
responsible document, realm, global object and event loop for the
current context. This effectively replaces ScriptExecutionContext, but
it cannot be removed in this commit as EventTarget still depends on it.
https://html.spec.whatwg.org/multipage/webappapis.html#environment-settings-object
This commit removes all exception related code:
Remove VM::exception(), VM::throw_exception() etc. Any leftover
throw_exception calls are moved to throw_completion.
The one method left is clear_exception() which is now a no-op. Most of
these calls are just to clear whatever exception might have been thrown
when handling a Completion. So to have a cleaner commit this will be
removed in a next commit.
It also removes the actual Exception and TemporaryClearException classes
since these are no longer used.
In any spot where the exception was actually used an attempt was made to
preserve that behavior. However since it is no longer tracked by the VM
we cannot access exceptions which were thrown in previous calls.
There are two such cases which might have different behavior:
- In Web::DOM::Document::interpreter() the on_call_stack_emptied hook
used to print any uncaught exception but this is now no longer
possible as the VM does not store uncaught exceptions.
- In js the code used to be interruptable by throwing an exception on
the VM. This is no longer possible but was already somewhat fragile
before as you could happen to throw an exception just before a VERIFY.
Previously, AK::Function would accept _any_ callable type, and try to
call it when called, first with the given set of arguments, then with
zero arguments, and if all of those failed, it would simply not call the
function and **return a value-constructed Out type**.
This lead to many, many, many hard to debug situations when someone
forgot a `const` in their lambda argument types, and many cases of
people taking zero arguments in their lambdas to ignore them.
This commit reworks the Function interface to not include any such
surprising behaviour, if your function instance is not callable with
the declared argument set of the Function, it can simply not be
assigned to that Function instance, end of story.
