Having all spec comments verbatim on their own line with no additions
made by us will make it easier to automate comparing said comments to
their current spec counterparts.
While adding spec comments to PerformEval, I noticed we were missing
multiple steps.
Namely, these were:
- Checking if the host will allow us to compile the string
(allowing LibWeb to perform CSP for eval)
- The parser's initial state depending on the environment around us
on direct eval:
- Allowing new.target via eval in functions
- Allowing super calls and super properties via eval in classes
- Disallowing the use of the arguments object in class field
initializers at eval's parse time
- Setting ScriptOrModule of eval's execution context
The spec allows us to apply the additional parsing steps in any order.
The method I have gone with is passing in a struct to the parser's
constructor, which overrides the parser's initial state to (dis)allow
the things stated above from the get-go.
This fixes 2 bugs in our current implementation:
* Properties deleted during iteration were still being iterated
* Properties with the same name in both the object and it's prototype
were iterated twice
The steps for creating a DeclarativeEnvironment for each iteration of a
for-loop can be done equivalently to the spec without following the spec
directly. For each binding creating in the loop's init expression, we:
1. Create a new binding in the new environment.
2. Grab the current value of the binding in the old environment.
3. Set the value in the new environment to the old value.
This can be replaced by initializing the bindings vector in the new
environment directly with the bindings in the old environment (but only
copying the bindings of the init statement).
When the initialization statement of a for-loop uses 'let', we must
create a new environment for each iteration of the for loop. The
bindings of the initialization statement are copied over to the new
environment. Since the bindings are created in the same order each time,
we can use that order to directly initialize the bindings and avoid any
O(n) lookups in this hot loop.
Before this was a mix of different strategies but copy_data_properties
does all of that in a spec way.
This fixes numeric properties in object spreading. And ensures that any
new properties added during spreading are not taken into account.
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.
This removes a number of vm.exception() checks which are now caught
directly by TRY. Make use of these checks in
{Global, Eval}DeclarationInstantiation and while we're here add spec
comments.
It seems the stack search does not find all functions because they are
kept in variants and other structs. This meant some function could be
cleaned up while we were evaluating a class meaning it would fail/crash
when attempting to run the functions.
The hard part of parsing them in import statements and calls was already
done so this is just removing some check which threw before on
assertions. And filtering the assertions based on the result of a new
host hook.
Because we can have arbitrary in- and export names with strings we can
have '*' and '' which means using '*' as an indicating namespace imports
failed / behaved incorrectly for string imports '*'.
We now use more specific types to indicate these special states instead
of these 'magic' string values.
Do note that 'default' is not actually a magic string value but one
specified by the spec. And you can in fact export the default value by
doing: `export { 1 as default }`.
This allows us to load modules from scripts.
This can be dangerous as it can load arbitrary files. Because of that it
fails and throws by default. Currently, only js and JavaScriptTestRunner
enable the default hook.
This also adds tests to test-js which test module code. Because we
form a spec perspective can't "enter" a module this is the easiest way
to run tests without having to modify test-js to have special cases for
modules.
To specify modules in test-js we use the extension '.mjs' this is to
ensure the files are not executed. We do still want to lint these files
so the prettier scripts have changed to look for '.mjs' files as well.
The big changes are:
- Allow strings as Module{Export, Import}Name
- Properly track declarations in default export statements
However, the spec is a little strange in that it allows function and
class declarations without a name in default export statements.
This is quite hard to fully implement without rewriting more of the
parser so for now this behavior is emulated by faking things with
function and class expressions. See the comments in
parse_export_statement for details on the hacks and where it goes wrong.
This also refactors interpreter creation to follow
InitializeHostDefinedRealm, but I couldn't fit it in the title :^)
This allows us to follow the spec much more closely rather than being
completely ad-hoc with just the parse node instead of having all the
surrounding data such as the realm of the parse node.
The interpreter creation refactor creates the global execution context
once and doesn't take it off the stack. This allows LibWeb to take the
global execution context and manually handle it, following the HTML
spec. The HTML spec calls this the "realm execution context" of the
environment settings object.
It also allows us to specify the globalThis type, as it can be
different from the global object type. For example, on the web, Window
global objects use a WindowProxy global this value to enforce the same
origin policy on operations like [[GetOwnProperty]].
Finally, it allows us to directly call Program::execute in perform_eval
and perform_shadow_realm_eval as this moves
global_declaration_instantiation into Interpreter::run
(ScriptEvaluation) as per the spec.
Note that this doesn't evalulate Source Text Modules yet or refactor
the bytecode interpreter, that's work for future us :^)
This patch was originally build by Luke for the environment settings
object change but was also needed for modules. So I (davidot) have
modified it with the new completion changes and setup for that.
Co-authored-by: davidot <davidot@serenityos.org>
Instead of using plain objects as Iterator records, causes confusion
about the object itself actually being its [[Iterator]] slot, and
requires non-standard type conversion shenanigans fpr the [[NextValue]]
and [[Done]] internal slots, implement a proper Iterator record struct
and use it throughout.
Also annotate the remaining Iterator AOs with spec comments while we're
here.
This includes:
- Parsing proper LabelledStatements with try_parse_labelled_statement()
- Removing LabelableStatement
- Implementing the LoopEvaluation semantics via loop_evaluation() in
each IterationStatement subclass; and IterationStatement evaluation
via {For,ForIn,ForOf,ForAwaitOf,While,DoWhile}Statement::execute()
- Updating ReturnStatement, BreakStatement and ContinueStatement to
return the appropriate completion types
- Basically reimplementing TryStatement and SwitchStatement according to
the spec, using completions
- Honoring result completion types in AsyncBlockStart and
OrdinaryCallEvaluateBody
- Removing any uses of the VM unwind mechanism - most importantly,
VM::throw_exception() now exclusively sets an exception and no longer
triggers any unwinding mechanism.
However, we already did a good job updating all of LibWeb and userland
applications to not use it, and the few remaining uses elsewhere don't
rely on unwinding AFAICT.
Instead of slapping 0..N labels on a statement like the current
LabelableStatement does, we need the spec's LabelledStatement for a
proper implementation of control flow using only completions - it always
has one label and one labelled statement - what appears to be 'multiple
labels' on the same statement is actually nested LabelledStatements.
Note that this is unused yet and will fully replace LabelableStatement
in the next commit.
This is another major milestone on our journey towards removing global
VM exception state :^)
Does pretty much exactly what it says on the tin: updating
ASTNode::execute() to return a Completion instead of a plain value. This
will *also* allow us to eventually remove the non-standard unwinding
mechanism and purely rely on the various completion types.
In the end this is a nicer API than having separate has_{value,target}()
and having to check those first, and then making another Optional from
the unwrapped value:
completion.has_value() ? completion.value() : Optional<Value> {}
// ^^^^^^^^^^^^^^^^^^
// Implicit creation of non-empty Optional<Value>
This way we need to unwrap the optional ourselves, but can easily pass
it to something else as well.
This is in anticipation of the AST using completions :^)
The spec has a note stating that resolve binding will always return a
reference whose [[ReferencedName]] field is name. However this is not
correct as the underlying method GetIdentifierReference may throw on
env.HasBinding(name) thus it can throw. However, there are some
scenarios where it cannot throw because the reference is known to exist
in that case we use MUST with a comment.
Exactly like in 99f9609, which fixed the same issue in CallExpression,
the spec tells us to *first* evaluate the arguments, if any, and *then*
check if the provided value is a constructor function.
