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LibJS: Introduce NativeJavaScriptBackedFunction

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This hosts the ability to compile and run JavaScript to implement
native functions. This is particularly useful for any native function
that is not a normal function, for example async functions such as
Array.fromAsync, which require yielding.

These functions are not allowed to observe anything from outside their
environment. Any global identifiers will instead be assumed to be a
reference to an abstract operation or a constant. The generator will
inject the appropriate bytecode if the name of the global identifier
matches a known name. Anything else will cause a code generation error.
This commit is contained in:
Luke Wilde 2025-11-06 19:00:36 +00:00 • committed by Andreas Kling
parent 899c6ebffc
commit a63b0cfaba
Notes: github-actions[bot] 2025-11-30 10:56:11 +00:00
21 changed files with 412 additions and 52 deletions
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32
Libraries/LibJS/Runtime/GeneratorObject.cpp
View file

@ -13,30 +13,50 @@
#include <LibJS/Runtime/GeneratorResult.h>
#include <LibJS/Runtime/GlobalObject.h>
#include <LibJS/Runtime/Iterator.h>
#include <LibJS/Runtime/NativeJavaScriptBackedFunction.h>
namespace JS {
GC_DEFINE_ALLOCATOR(GeneratorObject);
GC::Ref<GeneratorObject> GeneratorObject::create(Realm& realm, Value initial_value, ECMAScriptFunctionObject* generating_function, NonnullOwnPtr<ExecutionContext> execution_context)
GC::Ref<GeneratorObject> GeneratorObject::create(Realm& realm, Value initial_value, Variant<GC::Ref<ECMAScriptFunctionObject>, GC::Ref<NativeJavaScriptBackedFunction>> generating_function, NonnullOwnPtr<ExecutionContext> execution_context)
{
auto& vm = realm.vm();
// This is "g1.prototype" in figure-2 (https://tc39.es/ecma262/img/figure-2.png)
Value generating_function_prototype;
if (generating_function->kind() == FunctionKind::Async) {
auto kind = generating_function.visit(
[](auto function) {
return function->kind();
});
if (kind == FunctionKind::Async) {
// We implement async functions by transforming them to generator function in the bytecode
// interpreter. However an async function does not have a prototype and should not be
// changed thus we hardcode the prototype.
generating_function_prototype = realm.intrinsics().generator_prototype();
} else {
static Bytecode::PropertyLookupCache cache;
generating_function_prototype = MUST(generating_function->get(vm.names.prototype, cache));
generating_function_prototype = MUST(generating_function.visit([&vm](auto function) {
static Bytecode::PropertyLookupCache cache;
return function->get(vm.names.prototype, cache);
}));
}
GC::Ptr<Object> generating_function_prototype_object = nullptr;
if (!generating_function_prototype.is_nullish())
generating_function_prototype_object = MUST(generating_function_prototype.to_object(vm));
auto generating_executable = generating_function.visit(
[](GC::Ref<ECMAScriptFunctionObject> function) -> GC::Ref<Bytecode::Executable> {
return function->bytecode_executable().as_nonnull();
},
[](GC::Ref<NativeJavaScriptBackedFunction> function) -> GC::Ref<Bytecode::Executable> {
return function->bytecode_executable();
});
auto object = realm.create<GeneratorObject>(realm, generating_function_prototype_object, move(execution_context));
object->m_generating_function = generating_function;
object->m_generating_executable = generating_executable;
object->m_previous_value = initial_value;
return object;
}
@ -51,7 +71,7 @@ GeneratorObject::GeneratorObject(Realm& realm, Object* prototype, NonnullOwnPtr<
void GeneratorObject::visit_edges(Cell::Visitor& visitor)
{
Base::visit_edges(visitor);
visitor.visit(m_generating_function);
visitor.visit(m_generating_executable);
visitor.visit(m_previous_value);
m_execution_context->visit_edges(visitor);
}
@ -110,7 +130,7 @@ ThrowCompletionOr<GeneratorObject::IterationResult> GeneratorObject::execute(VM&
// We should never enter `execute` again after the generator is complete.
VERIFY(next_block.has_value());
auto result_value = bytecode_interpreter.run_executable(vm.running_execution_context(), *m_generating_function->bytecode_executable(), next_block, completion_cell);
auto result_value = bytecode_interpreter.run_executable(vm.running_execution_context(), *m_generating_executable, next_block, completion_cell);
vm.pop_execution_context();