This is a huge patch, I know. In hindsight this perhaps could've been
done slightly more incremental, but I started and then fixed everything
until it worked, and here we are. I tried splitting of some completely
unrelated changes into separate commits, however. Anyway.
This is a rewrite of most of Object, and by extension large parts of
Array, Proxy, Reflect, String, TypedArray, and some other things.
What we already had worked fine for about 90% of things, but getting the
last 10% right proved to be increasingly difficult with the current code
that sort of grew organically and is only very loosely based on the
spec - this became especially obvious when we started fixing a large
number of test262 failures.
Key changes include:
- 1:1 matching function names and parameters of all object-related
functions, to avoid ambiguity. Previously we had things like put(),
which the spec doesn't have - as a result it wasn't always clear which
need to be used.
- Better separation between object abstract operations and internal
methods - the former are always the same, the latter can be overridden
(and are therefore virtual). The internal methods (i.e. [[Foo]] in the
spec) are now prefixed with 'internal_' for clarity - again, it was
previously not always clear which AO a certain method represents,
get() could've been both Get and [[Get]] (I don't know which one it
was closer to right now).
Note that some of the old names have been kept until all code relying
on them is updated, but they are now simple wrappers around the
closest matching standard abstract operation.
- Simplifications of the storage layer: functions that write values to
storage are now prefixed with 'storage_' to make their purpose clear,
and as they are not part of the spec they should not contain any steps
specified by it. Much functionality is now covered by the layers above
it and was removed (e.g. handling of accessors, attribute checks).
- PropertyAttributes has been greatly simplified, and is being replaced
by PropertyDescriptor - a concept similar to the current
implementation, but more aligned with the actual spec. See the commit
message of the previous commit where it was introduced for details.
- As a bonus, and since I had to look at the spec a whole lot anyway, I
introduced more inline comments with the exact steps from the spec -
this makes it super easy to verify correctness.
- East-const all the things.
As a result of all of this, things are much more correct but a bit
slower now. Retaining speed wasn't a consideration at all, I have done
no profiling of the new code - there might be low hanging fruits, which
we can then harvest separately.
Special thanks to Idan for helping me with this by tracking down bugs,
updating everything outside of LibJS to work with these changes (LibWeb,
Spreadsheet, HackStudio), as well as providing countless patches to fix
regressions I introduced - there still are very few (we got it down to
5), but we also get many new passing test262 tests in return. :^)
Co-authored-by: Idan Horowitz <idan.horowitz@gmail.com>
Specifically, this now explicitly takes the length, adds missing
exceptions checks to calls with user-supplied lengths, takes and uses
the prototype argument, and fixes some spec non-conformance in
ArrayConstructor and its native functions around the use of ArrayCreate
ResolveBinding now matches the spec, while the non-conforming parts
are moved to GetIdentifierReference.
Implementing this properly requires variable bindings.
This is used by VM::call_internal() and VM::construct() which roughly
map to function objects' [[Call]] and [[Construct]] slots in the spec.
Reorganizing this code revealed something weird: NativeFunction gets
its strictness by checking VM::in_strict_mode(). In other words,
it inherits the strict flag from the caller context. This is quite
weird, but many test-js tests rely on it, so let's preserve it until
we can think of something nicer.
This patch adds a new ArgumentsObject class to represent what the spec
calls "Arguments Exotic Objects"
These are constructed by the new CreateMappedArgumentsObject when the
`arguments` identifier is resolved in a callee context.
The implementation is incomplete and doesn't yet support mapping of
the parameter variables to the indexed properties of `arguments`.
This patch implements the IsSimpleParameterList static semantics for
ordinary function objects.
We now also create an unmapped arguments object for callee contexts
with non-simple parameter lists, instead of only doing it in strict
mode. Covered by test262.
Our Reference class now has the same fields as the spec:
- Base (a non-nullish value, an environment record, or `unresolvable`)
- Referenced Name (the name of the binding)
- Strict (whether the reference originated in strict mode code)
- ThisValue (if non-empty, the reference represents a `super` keyword)
The main difference from before is that we now resolve the environment
record that a reference interacts with. Previously we simply resolved
to either "local variable" or "global variable".
The associated abstract operations are still largely non-conforming,
since we don't yet implement proper variable bindings. But this patch
should at least fix a handful of test262 cases. :^)
There's one minor regression: some TypeError message strings get
a little worse due to doing a RequireObjectCoercible earlier in the
evaluation of MemberExpression.
At the moment these environments are always the same as the lexical
ones, so this didn't cause any trouble. Once we start separating them
we have to make sure both environments are protected.
This matches what ECMAScript calls it. Also make it a JS::Function*
instead of a generic Value, since it will always either be a function
object or null.
We had a cached shape for environment records to make instantiating
them fast. Now that environment records don't inherit from JS::Object,
we can just get rid of this. :^)
These represent the outermost scope in the environment record
hierarchy. The spec says they should be a "composite" of two things:
- An ObjectEnvironmentRecord wrapping the global object
- A DeclarativeEnvironmentRecord for other declarations
It's not yet clear to me how this should work, so this patch only
implements the first part, an object record wrapping the global object.
To better follow the spec, we need to distinguish between the current
execution context's lexical environment and variable environment.
This patch moves us to having two record pointers, although both of
them point at the same environment records for now.
This patch adds FunctionEnvironmentRecord as a subclass of the existing
DeclarativeEnvironmentRecord. Things that are specific to function
environment records move into there, simplifying the base.
Most of the abstract operations related to function environment records
are rewritten to match the spec exactly. I also had to implement
GetThisEnvironment() and GetSuperConstructor() to keep tests working
after the changes, so that's nice as well. :^)
This patch makes the following renames:
- get_from_scope() => get_from_environment_record()
- put_to_scope() => put_into_environment_record()
- delete_from_scope() => delete_from_environment_record()
This patch makes the following name changes:
- ScopeObject => EnvironmentRecord
- LexicalEnvironment => DeclarativeEnvironmentRecord
- WithScope => ObjectEnvironmentRecord
This now matches the spec's OrdinaryObjectCreate() across the board:
instead of implicitly setting the created object's prototype to
%Object.prototype% and then in many cases setting it to a nullptr right
away, it now has an 'Object* prototype' parameter with _no default
value_. This makes the code easier to compare with the spec, very clear
in terms of what prototype is being used as well as avoiding unnecessary
shape transitions.
Also fixes a couple of cases were we weren't setting the correct
prototype.
There's no reason to assume that the object would not be empty (as in
having own properties), so let's follow our existing pattern of
Type::create(...) and simply call it 'create'.
We were doing a *lot* of string-to-int conversion while creating a new
global object. This happened because Object::put() would try to convert
the property name (string) to an integer to see if it refers to an
indexed property.
Sidestep this issue by using PropertyName for the CommonPropertyNames
struct on VM (vm.names.foo), and giving PropertyName a flag that tells
us whether it's a string that *may be* a number.
All CommonPropertyNames are set up so they are known to not be numbers.
As mentioned on Discord earlier, we'll add these to all new functions
going forward - this is the backfill. Reasons:
- It makes you look at the spec, implementing based on MDN or V8
behavior is a no-go
- It makes finding the various functions that are non-compliant easier,
in the future everything should either have such a comment or, if it's
not from the spec at all, a comment explaining why that is the case
- It makes it easier to check whether a certain abstract operation is
implemented in LibJS, not all of them use the same name as the spec.
E.g. RejectPromise() is Promise::reject()
- It makes it easier to reason about vm.arguments(), e.g. when the
function has a rest parameter
- It makes it easier to see whether a certain function is from a
proposal or Annex B
Also:
- Add arguments to all functions and abstract operations that already
had a comment
- Fix some outdated section numbers
- Replace some ecma-international.org URLs with tc39.es
This was creating a ton of pointless busywork for the garbage collector
and can be avoided simply by tolerating that the current call frame has
a null scope object for the duration of a NativeFunction activation.
This is just a simple helper that dumps the current VM call stack
to the debug console. I find myself rewriting this function over and
over, so let's just have it in the tree.
There's no reason at all for this to be a string or to accept arbitrary
values - just because it's displayed as strings in the spec doesn't mean
we have to do the same :^)
In HackStudio's Debugger a custom GlobalObject is used to reflect
debugger variables into the JS scope by overriding GlobalObject's
get method. However, when throwing a custom error during that lookup
it was replaced with the generic "not found" js exception. This patch
makes it instead pass along the custom error.
LibWeb is now responsible for logging unhandled exceptions itself,
which means set_should_log_exceptions() is no longer used and can be
removed. It turned out to be not the best option for web page exception
logging, as we would have no indication regarding whether the exception
was later handled of not.
This is very similar to AK::TemporaryChange (and in fact replaces one
use of it), but since we can't directly set VM's m_exception from
outside of the VM, we need something more sophisticated.
Sometimes we need to temporarily remove the stored exception for some
other operation to succeed (e.g. anything that uses call(), as well as
get_without_side_effects()) and later restore it - the boilerplate code
required for this is annoying enough to justify a helper.
