Now that it only needs to deal with ECMAScriptFunctionObject via
internal_call() / internal_construct(), we can:
- Remove the generic FunctionObject parameter
- Move it from the VM to ECMAScriptFunctionObject
- Make it private
Now that it only needs to deal with ECMAScriptFunctionObject via
internal_call() / internal_construct(), we can:
- Remove the generic FunctionObject parameter
- Move it from the VM to ECMAScriptFunctionObject
- Make it private
This patch implements:
- Spec compliant [[Call]] and [[Construct]] internal slots, as virtual
FunctionObject::internal_{call,construct}(). These effectively replace
the old virtual FunctionObject::{call,construct}(), but with several
advantages:
- Clear and consistent naming, following the object internal methods
- Use of completions
- internal_construct() returns an Object, and not Value! This has been
a source of confusion for a long time, since in the spec there's
always an Object returned but the Value return type in LibJS meant
that this could not be fully trusted and something could screw you
over.
- Arguments are passed explicitly in form of a MarkedValueList,
allowing manipulation (BoundFunction). We still put them on the
execution context as a lot of code depends on it (VM::arguments()),
but not from the Call() / Construct() AOs anymore, which now allows
for bypassing them and invoking [[Call]] / [[Construct]] directly.
Nothing but Call() / Construct() themselves do that at the moment,
but future additions to ECMA262 or already existing web specs might.
- Spec compliant, standalone Call() and Construct() AOs: currently the
closest we have is VM::{call,construct}(), but those try to cater to
all the different function object subclasses at once, resulting in a
horrible mess and calling AOs with functions they should never be
called with; most prominently PrepareForOrdinaryCall and
OrdinaryCallBindThis, which are only for ECMAScriptFunctionObject.
As a result this also contains an implicit optimization: we no longer
need to create a new function environment for NativeFunctions - which,
worth mentioning, is what started this whole crusade in the first place
:^)
This patch introduces the "environment coordinate" concept, which
encodes the distance from a variable access to the binding it ends up
resolving to.
EnvironmentCoordinate has two fields:
- hops: The number of hops up the lexical environment chain we have
to make before getting to the resolved binding.
- index: The index of the resolved binding within its declarative
environment record.
Whenever a variable lookup resolves somewhere inside a declarative
environment, we now cache the coordinates and reuse them in subsequent
lookups. This is achieved via a coordinate cache in JS::Identifier.
Note that non-strict direct eval() breaks this optimization and so it
will not be performed if the resolved environment has been permanently
screwed by eval().
This makes variable access *significantly* faster. :^)
VM::resolve_binding() can now return a Reference that knows the exact
binding index if it's pointing into a DeclarativeEnvironment.
Reading/writing through the Reference will now use direct environment
access when possible.
This will be used by LibWeb to squirrel away the stack while performing
a microtask checkpoint in some cases. VM will simply consider saved
execution context stacks as GC roots as well.
Before this we used an ad-hoc combination of references and 'variables'
stored in a hashmap. This worked in most cases but is not spec like.
Additionally hoisting, dynamically naming functions and scope analysis
was not done properly.
This patch fixes all of that by:
- Implement BindingInitialization for destructuring assignment.
- Implementing a new ScopePusher which tracks the lexical and var
scoped declarations. This hoists functions to the top level if no
lexical declaration name overlaps. Furthermore we do checking of
redeclarations in the ScopePusher now requiring less checks all over
the place.
- Add methods for parsing the directives and statement lists instead
of having that code duplicated in multiple places. This allows
declarations to pushed to the appropriate scope more easily.
- Remove the non spec way of storing 'variables' in
DeclarativeEnvironment and make Reference follow the spec instead of
checking both the bindings and 'variables'.
- Remove all scoping related things from the Interpreter. And instead
use environments as specified by the spec. This also includes fixing
that NativeFunctions did not produce a valid FunctionEnvironment
which could cause issues with callbacks and eval. All
FunctionObjects now have a valid NewFunctionEnvironment
implementation.
- Remove execute_statements from Interpreter and instead use
ASTNode::execute everywhere this simplifies AST.cpp as you no longer
need to worry about which method to call.
- Make ScopeNodes setup their own environment. This uses four
different methods specified by the spec
{Block, Function, Eval, Global}DeclarationInstantiation with the
annexB extensions.
- Implement and use NamedEvaluation where specified.
Additionally there are fixes to things exposed by these changes to eval,
{for, for-in, for-of} loops and assignment.
Finally it also fixes some tests in test-js which where passing before
but not now that we have correct behavior :^).
Also add the internal slot names as comments, and separate them into
groups of spec and non-spec members.
This will make it easier to compare the implementation code with the
spec, as well as identify internal slots currently missing or only
present on FunctionObject.
The old name is the result of the perhaps somewhat confusingly named
abstract operation OrdinaryFunctionCreate(), which creates an "ordinary
object" (https://tc39.es/ecma262/#ordinary-object) in contrast to an
"exotic object" (https://tc39.es/ecma262/#exotic-object).
However, the term "Ordinary Function" is not used anywhere in the spec,
instead the created object is referred to as an "ECMAScript Function
Object" (https://tc39.es/ecma262/#sec-ecmascript-function-objects), so
let's call it that.
The "ordinary" vs. "exotic" distinction is important because there are
also "Built-in Function Objects", which can be either implemented as
ordinary ECMAScript function objects, or as exotic objects (our
NativeFunction).
More work needs to be done to move a lot of infrastructure to
ECMAScriptFunctionObject in order to make FunctionObject nothing more
than an interface for objects that implement [[Call]] and optionally
[[Construct]].
'bindings' is the spec-compliant version of 'variables', but we were
simply not even looking at them, which made things using bindings (such
as named function expressions) break in unexpected ways after the move
to using references in call expressions.
Co-Authored-By: davidot <david.tuin@gmail.com>
This got changed in the spec at some point, replacing the assertion in
step 1 with "... and newTarget (an Object or undefined)" in the
parameter description.
Subsequently, there's now one step less, so the numbers all change.
This is where the spec wants to have it. Requires a couple of hacks as
currently everything that needs a Realm actually has a GlobalObject, so
we need to go via the Interpreter.
Instead of hardcoding the environment's global object as the return
value of GlobalEnvironment::global_this_value(), it now stores an Object
reference which is passed to the constructor for this purpose.
From the spec (https://tc39.es/ecma262/#sec-global-environment-records):
[[GlobalThisValue]] | Object | The value returned by this in global
scope. Hosts may provide any ECMAScript Object value.
The test262 tests under RegExp/property-escapes/generated will invoke
Reflect.apply with up to 10,000 arguments at a time. In LibJS, when the
call stack reached VM::call_internal, we transfer those arguments from
a MarkedValueList to the execution context's arguments Vector.
Because these types differ (MarkedValueList is a Vector<Value, 32>), the
arguments are copied rather than moved. By changing the arguments vector
to a MarkedValueList, we can properly move the passed arguments over.
This shaves about 2 seconds off the following test262 test (from 15sec):
RegExp/property-escapes/generated/General_Category_-_Decimal_Number.js
