script/runtime/

script_runtime.rs

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/. */

//! The script runtime contains common traits and structs commonly used by the
//! script thread, the dom, and the worker threads.

#![expect(dead_code)]

use core::ffi::c_char;
use std::cell::{Cell, LazyCell, RefCell};
use std::collections::{HashMap, HashSet};
use std::ffi::{CStr, CString};
use std::io::{Write, stdout};
use std::ops::{Deref, DerefMut};
use std::os::raw::c_void;
use std::ptr::NonNull;
use std::rc::Weak;
use std::time::Instant;
use std::{os, ptr};

use background_hang_monitor_api::ScriptHangAnnotation;
use js::context::JSContext;
use js::conversions::jsstr_to_string;
use js::gc::StackGCVector;
use js::glue::{
    DispatchablePointer, RUST_js_GetErrorMessage, RegisterScriptEnvironmentPreparer,
    RunScriptEnvironmentPreparerClosure, SetBuildId, StreamConsumerConsumeChunk,
    StreamConsumerNoteResponseURLs, StreamConsumerStreamEnd, StreamConsumerStreamError,
};
use js::jsapi::{
    AsmJSOption, BuildIdCharVector, CompilationType, Dispatchable_MaybeShuttingDown, GCDescription,
    GCOptions, GCProgress, GCReason, Handle as RawHandle, HandleObject, HandleString,
    HandleValue as RawHandleValue, Heap, JSContext as RawJSContext, JSGCParamKey, JSGCStatus,
    JSJitCompilerOption, JSObject, JSSecurityCallbacks, JSString, JSTracer, MimeType,
    MutableHandleString, PromiseRejectionHandlingState, RuntimeCode,
    ScriptEnvironmentPreparer_Closure, SetProcessBuildIdOp, StreamConsumer as JSStreamConsumer,
};
use js::jsval::{JSVal, UndefinedValue};
use js::panic::wrap_panic;
use js::realm::CurrentRealm;
pub(crate) use js::rust::ThreadSafeJSContext;
use js::rust::wrappers2::{
    CollectServoSizes, ContextOptionsRef, DispatchableRun, InitConsumeStreamCallback,
    JS_AddExtraGCRootsTracer, JS_GetPromiseResult, JS_InitDestroyPrincipalsCallback,
    JS_InitReadPrincipalsCallback, JS_NewStringCopyUTF8N, JS_SetGCCallback, JS_SetGCParameter,
    JS_SetGlobalJitCompilerOption, JS_SetOffthreadIonCompilationEnabled, JS_SetSecurityCallbacks,
    SetDOMCallbacks, SetGCSliceCallback, SetPreserveWrapperCallbacks,
    SetPromiseRejectionTrackerCallback, SetUpEventLoopDispatch,
};
use js::rust::{
    Handle, HandleObject as RustHandleObject, HandleValue, IntoHandle, ParentRuntime,
    Runtime as RustRuntime, Trace,
};
use malloc_size_of::MallocSizeOfOps;
use malloc_size_of_derive::MallocSizeOf;
use profile_traits::mem::{Report, ReportKind};
use profile_traits::path;
use profile_traits::time::ProfilerCategory;
use script_bindings::reflector::DomObject;
use script_bindings::script_runtime::{mark_runtime_dead, runtime_is_alive, temp_cx};
use script_bindings::settings_stack::run_a_script;
use servo_config::opts::{self, DiagnosticsLoggingOption};
use servo_config::pref;
use servo_url::ServoUrl;
use style::thread_state::{self, ThreadState};

use crate::dom::bindings::codegen::Bindings::ResponseBinding::Response_Binding::ResponseMethods;
use crate::dom::bindings::codegen::Bindings::ResponseBinding::ResponseType as DOMResponseType;
use crate::dom::bindings::codegen::UnionTypes::TrustedScriptOrString;
use crate::dom::bindings::conversions::{
    get_dom_class, private_from_object, root_from_handleobject, root_from_object,
};
use crate::dom::bindings::error::{Error, report_pending_exception, throw_dom_exception};
use crate::dom::bindings::inheritance::Castable;
use crate::dom::bindings::refcounted::{
    LivePromiseReferences, Trusted, TrustedPromise, trace_refcounted_objects,
};
use crate::dom::bindings::reflector::DomGlobal;
use crate::dom::bindings::root::trace_roots;
use crate::dom::bindings::str::DOMString;
use crate::dom::bindings::utils::DOM_CALLBACKS;
use crate::dom::bindings::{principals, settings_stack};
use crate::dom::console::{Console, stringify_handle_value};
use crate::dom::csp::CspReporting;
use crate::dom::event::{Event, EventBubbles, EventCancelable};
use crate::dom::eventtarget::EventTarget;
use crate::dom::globalscope::GlobalScope;
use crate::dom::promise::Promise;
use crate::dom::promiserejectionevent::PromiseRejectionEvent;
use crate::dom::response::Response;
use crate::dom::trustedtypes::trustedscript::TrustedScript;
use crate::dom::window::Window;
use crate::engine::handle::current_js_engine_handle;
use crate::messaging::{CommonScriptMsg, ScriptEventLoopSender};
use crate::modules::script_module::EnsureModuleHooksInitialized;
use crate::realms::enter_auto_realm;
use crate::runtime::job_queue::{JobQueue, job_queue_clear};
use crate::tasks::task_source::TaskSourceName;
use crate::{DomTypeHolder, ScriptThread};

static SECURITY_CALLBACKS: JSSecurityCallbacks = JSSecurityCallbacks {
    contentSecurityPolicyAllows: Some(content_security_policy_allows),
    codeForEvalGets: Some(code_for_eval_gets),
    subsumes: Some(principals::subsumes),
};

#[derive(Clone, Copy, Debug, Eq, Hash, JSTraceable, MallocSizeOf, PartialEq)]
pub(crate) enum ScriptThreadEventCategory {
    SpawnPipeline,
    ConstellationMsg,
    DatabaseAccessEvent,
    DevtoolsMsg,
    DocumentEvent,
    FileRead,
    FontLoading,
    FormPlannedNavigation,
    GeolocationEvent,
    ImageCacheMsg,
    InputEvent,
    NavigationAndTraversalEvent,
    NetworkEvent,
    PortMessage,
    Rendering,
    Resize,
    ScriptEvent,
    SetScrollState,
    SetViewport,
    StylesheetLoad,
    TimerEvent,
    UpdateReplacedElement,
    WebSocketEvent,
    WorkerEvent,
    WorkletEvent,
    ServiceWorkerEvent,
    EnterFullscreen,
    ExitFullscreen,
    PerformanceTimelineTask,
    #[cfg(feature = "webgpu")]
    WebGPUMsg,
}

impl From<ScriptThreadEventCategory> for ProfilerCategory {
    fn from(category: ScriptThreadEventCategory) -> Self {
        match category {
            ScriptThreadEventCategory::SpawnPipeline => ProfilerCategory::ScriptSpawnPipeline,
            ScriptThreadEventCategory::ConstellationMsg => ProfilerCategory::ScriptConstellationMsg,
            ScriptThreadEventCategory::DatabaseAccessEvent => {
                ProfilerCategory::ScriptDatabaseAccessEvent
            },
            ScriptThreadEventCategory::DevtoolsMsg => ProfilerCategory::ScriptDevtoolsMsg,
            ScriptThreadEventCategory::DocumentEvent => ProfilerCategory::ScriptDocumentEvent,
            ScriptThreadEventCategory::EnterFullscreen => ProfilerCategory::ScriptEnterFullscreen,
            ScriptThreadEventCategory::ExitFullscreen => ProfilerCategory::ScriptExitFullscreen,
            ScriptThreadEventCategory::FileRead => ProfilerCategory::ScriptFileRead,
            ScriptThreadEventCategory::FontLoading => ProfilerCategory::ScriptFontLoading,
            ScriptThreadEventCategory::FormPlannedNavigation => {
                ProfilerCategory::ScriptPlannedNavigation
            },
            ScriptThreadEventCategory::GeolocationEvent => ProfilerCategory::ScriptGeolocationEvent,
            ScriptThreadEventCategory::NavigationAndTraversalEvent => {
                ProfilerCategory::ScriptNavigationAndTraversalEvent
            },
            ScriptThreadEventCategory::ImageCacheMsg => ProfilerCategory::ScriptImageCacheMsg,
            ScriptThreadEventCategory::InputEvent => ProfilerCategory::ScriptInputEvent,
            ScriptThreadEventCategory::NetworkEvent => ProfilerCategory::ScriptNetworkEvent,
            ScriptThreadEventCategory::PerformanceTimelineTask => {
                ProfilerCategory::ScriptPerformanceEvent
            },
            ScriptThreadEventCategory::PortMessage => ProfilerCategory::ScriptPortMessage,
            ScriptThreadEventCategory::Resize => ProfilerCategory::ScriptResize,
            ScriptThreadEventCategory::Rendering => ProfilerCategory::ScriptRendering,
            ScriptThreadEventCategory::ScriptEvent => ProfilerCategory::ScriptEvent,
            ScriptThreadEventCategory::ServiceWorkerEvent => {
                ProfilerCategory::ScriptServiceWorkerEvent
            },
            ScriptThreadEventCategory::SetScrollState => ProfilerCategory::ScriptSetScrollState,
            ScriptThreadEventCategory::SetViewport => ProfilerCategory::ScriptSetViewport,
            ScriptThreadEventCategory::StylesheetLoad => ProfilerCategory::ScriptStylesheetLoad,
            ScriptThreadEventCategory::TimerEvent => ProfilerCategory::ScriptTimerEvent,
            ScriptThreadEventCategory::UpdateReplacedElement => {
                ProfilerCategory::ScriptUpdateReplacedElement
            },
            ScriptThreadEventCategory::WebSocketEvent => ProfilerCategory::ScriptWebSocketEvent,
            ScriptThreadEventCategory::WorkerEvent => ProfilerCategory::ScriptWorkerEvent,
            ScriptThreadEventCategory::WorkletEvent => ProfilerCategory::ScriptWorkletEvent,
            #[cfg(feature = "webgpu")]
            ScriptThreadEventCategory::WebGPUMsg => ProfilerCategory::ScriptWebGPUMsg,
        }
    }
}

impl From<ScriptThreadEventCategory> for ScriptHangAnnotation {
    fn from(category: ScriptThreadEventCategory) -> Self {
        match category {
            ScriptThreadEventCategory::SpawnPipeline => ScriptHangAnnotation::SpawnPipeline,
            ScriptThreadEventCategory::ConstellationMsg => ScriptHangAnnotation::ConstellationMsg,
            ScriptThreadEventCategory::DatabaseAccessEvent => {
                ScriptHangAnnotation::DatabaseAccessEvent
            },
            ScriptThreadEventCategory::DevtoolsMsg => ScriptHangAnnotation::DevtoolsMsg,
            ScriptThreadEventCategory::DocumentEvent => ScriptHangAnnotation::DocumentEvent,
            ScriptThreadEventCategory::InputEvent => ScriptHangAnnotation::InputEvent,
            ScriptThreadEventCategory::FileRead => ScriptHangAnnotation::FileRead,
            ScriptThreadEventCategory::FontLoading => ScriptHangAnnotation::FontLoading,
            ScriptThreadEventCategory::FormPlannedNavigation => {
                ScriptHangAnnotation::FormPlannedNavigation
            },
            ScriptThreadEventCategory::GeolocationEvent => ScriptHangAnnotation::GeolocationEvent,
            ScriptThreadEventCategory::NavigationAndTraversalEvent => {
                ScriptHangAnnotation::NavigationAndTraversalEvent
            },
            ScriptThreadEventCategory::ImageCacheMsg => ScriptHangAnnotation::ImageCacheMsg,
            ScriptThreadEventCategory::NetworkEvent => ScriptHangAnnotation::NetworkEvent,
            ScriptThreadEventCategory::Rendering => ScriptHangAnnotation::Rendering,
            ScriptThreadEventCategory::Resize => ScriptHangAnnotation::Resize,
            ScriptThreadEventCategory::ScriptEvent => ScriptHangAnnotation::ScriptEvent,
            ScriptThreadEventCategory::SetScrollState => ScriptHangAnnotation::SetScrollState,
            ScriptThreadEventCategory::SetViewport => ScriptHangAnnotation::SetViewport,
            ScriptThreadEventCategory::StylesheetLoad => ScriptHangAnnotation::StylesheetLoad,
            ScriptThreadEventCategory::TimerEvent => ScriptHangAnnotation::TimerEvent,
            ScriptThreadEventCategory::UpdateReplacedElement => {
                ScriptHangAnnotation::UpdateReplacedElement
            },
            ScriptThreadEventCategory::WebSocketEvent => ScriptHangAnnotation::WebSocketEvent,
            ScriptThreadEventCategory::WorkerEvent => ScriptHangAnnotation::WorkerEvent,
            ScriptThreadEventCategory::WorkletEvent => ScriptHangAnnotation::WorkletEvent,
            ScriptThreadEventCategory::ServiceWorkerEvent => {
                ScriptHangAnnotation::ServiceWorkerEvent
            },
            ScriptThreadEventCategory::EnterFullscreen => ScriptHangAnnotation::EnterFullscreen,
            ScriptThreadEventCategory::ExitFullscreen => ScriptHangAnnotation::ExitFullscreen,
            ScriptThreadEventCategory::PerformanceTimelineTask => {
                ScriptHangAnnotation::PerformanceTimelineTask
            },
            ScriptThreadEventCategory::PortMessage => ScriptHangAnnotation::PortMessage,
            #[cfg(feature = "webgpu")]
            ScriptThreadEventCategory::WebGPUMsg => ScriptHangAnnotation::WebGPUMsg,
        }
    }
}

#[expect(unsafe_code)]
/// <https://html.spec.whatwg.org/multipage/#the-hostpromiserejectiontracker-implementation>
unsafe extern "C" fn promise_rejection_tracker(
    cx: *mut RawJSContext,
    muted_errors: bool,
    promise: HandleObject,
    state: PromiseRejectionHandlingState,
    _data: *mut c_void,
) {
    // Step 1. Let script be the running script.
    // Step 2. If script is a classic script and script's muted errors is true, then return.
    if muted_errors {
        return;
    }

    // Step 3.
    // SAFETY: it is safe to construct a JSContext from engine hook.
    let mut cx = unsafe { JSContext::from_ptr(NonNull::new(cx).unwrap()) };
    let mut realm = CurrentRealm::assert(&mut cx);

    let global = GlobalScope::from_current_realm(&mut realm);
    let cx = &mut realm;

    wrap_panic(&mut || {
        match state {
            // Step 4.
            PromiseRejectionHandlingState::Unhandled => {
                global.add_uncaught_rejection(promise);
            },
            // Step 5.
            PromiseRejectionHandlingState::Handled => {
                // Step 5-1.
                if global
                    .get_uncaught_rejections()
                    .borrow()
                    .contains(&Heap::boxed(promise.get()))
                {
                    global.remove_uncaught_rejection(promise);
                    return;
                }

                // Step 5-2.
                if !global
                    .get_consumed_rejections()
                    .borrow()
                    .contains(&Heap::boxed(promise.get()))
                {
                    return;
                }

                // Step 5-3.
                global.remove_consumed_rejection(promise);

                let target = Trusted::new(global.upcast::<EventTarget>());
                let promise =
                    Promise::new_with_js_promise(cx, unsafe { Handle::from_raw(promise) });
                let trusted_promise = TrustedPromise::from(&promise);

                // Step 5-4.
                global.task_manager().dom_manipulation_task_source().queue(
                task!(rejection_handled_event: move |cx| {
                    let target = target.root();
                    let root_promise = trusted_promise.root(cx);

                    rooted!(&in(cx) let mut reason = UndefinedValue());
                    unsafe {
                        JS_GetPromiseResult(root_promise.reflector().get_jsobject(), reason.handle_mut());
                    }

                    let event = PromiseRejectionEvent::new(
                        cx,
                        &target.global(),
                        atom!("rejectionhandled"),
                        EventBubbles::DoesNotBubble,
                        EventCancelable::Cancelable,
                        &root_promise,
                        reason.handle(),
                    );

                    event.upcast::<Event>().fire(cx, &target);
                })
                );
            },
        };
    })
}

#[expect(unsafe_code)]
fn safely_convert_null_to_string(cx: &JSContext, str_: HandleString) -> DOMString {
    DOMString::from(match std::ptr::NonNull::new(*str_) {
        None => String::new(),
        Some(str_) => unsafe { jsstr_to_string(cx, str_) },
    })
}

#[expect(unsafe_code)]
unsafe extern "C" fn code_for_eval_gets(
    cx: *mut RawJSContext,
    code: HandleObject,
    code_for_eval: MutableHandleString,
) -> bool {
    // SAFETY: We are in SM hook
    let (mut cx, code) = unsafe {
        (
            JSContext::from_ptr(NonNull::new(cx).unwrap()),
            RustHandleObject::from_raw(code),
        )
    };
    let cx = &mut cx;
    if let Ok(trusted_script) = root_from_handleobject::<TrustedScript>(cx, code) {
        let script_str = trusted_script.data().str();
        let s = js::conversions::Utf8Chars::from(&*script_str);
        let new_string = unsafe { JS_NewStringCopyUTF8N(cx, &*s as *const _) };
        code_for_eval.set(new_string);
    }
    true
}

#[expect(unsafe_code)]
unsafe extern "C" fn content_security_policy_allows(
    cx: *mut RawJSContext,
    runtime_code: RuntimeCode,
    code_string: HandleString,
    compilation_type: CompilationType,
    parameter_strings: RawHandle<StackGCVector<*mut JSString>>,
    body_string: HandleString,
    parameter_args: RawHandle<StackGCVector<JSVal>>,
    body_arg: RawHandleValue,
    can_compile_strings: *mut bool,
) -> bool {
    let mut allowed = false;
    // SAFETY: We are in SM hook
    let mut cx = unsafe { JSContext::from_ptr(NonNull::new(cx).unwrap()) };
    let cx = &mut cx;
    wrap_panic(&mut || {
        // SpiderMonkey provides null pointer when executing webassembly.
        let mut realm = CurrentRealm::assert(cx);
        let global = GlobalScope::from_current_realm(&mut realm);
        let csp_list = global.get_csp_list();

        // If we don't have any CSP checks to run, short-circuit all logic here
        allowed = csp_list.is_none() ||
            match runtime_code {
                RuntimeCode::JS => {
                    let parameter_strings = unsafe { Handle::from_raw(parameter_strings) };
                    let parameter_strings_length = parameter_strings.len();
                    let mut parameter_strings_vec =
                        Vec::with_capacity(parameter_strings_length as usize);

                    for i in 0..parameter_strings_length {
                        let Some(str_) = parameter_strings.at(i) else {
                            unreachable!();
                        };
                        parameter_strings_vec.push(safely_convert_null_to_string(cx, str_.into()));
                    }

                    let parameter_args = unsafe { Handle::from_raw(parameter_args) };
                    let parameter_args_length = parameter_args.len();
                    let mut parameter_args_vec = Vec::with_capacity(parameter_args_length as usize);

                    for i in 0..parameter_args_length {
                        let Some(arg) = parameter_args.at(i) else {
                            unreachable!();
                        };
                        let value = arg.into_handle().get();
                        if value.is_object() {
                            if let Ok(trusted_script) =
                                unsafe { root_from_object::<TrustedScript>(cx, value.to_object()) }
                            {
                                parameter_args_vec
                                    .push(TrustedScriptOrString::TrustedScript(trusted_script));
                            } else {
                                // It's not a trusted script but a different object. Treat it
                                // as if it is a string, since we don't need the actual contents
                                // of the object.
                                parameter_args_vec
                                    .push(TrustedScriptOrString::String(DOMString::new()));
                            }
                        } else if value.is_string() {
                            // We don't need to know the specific string, only that it is untrusted
                            parameter_args_vec
                                .push(TrustedScriptOrString::String(DOMString::new()));
                        } else {
                            unreachable!();
                        }
                    }

                    let code_string = safely_convert_null_to_string(cx, code_string);
                    let body_string = safely_convert_null_to_string(cx, body_string);

                    TrustedScript::can_compile_string_with_trusted_type(
                        cx,
                        &global,
                        code_string,
                        compilation_type,
                        parameter_strings_vec,
                        body_string,
                        parameter_args_vec,
                        unsafe { HandleValue::from_raw(body_arg) },
                    )
                },
                RuntimeCode::WASM => global
                    .get_csp_list()
                    .is_wasm_evaluation_allowed(cx, &global),
            };
    });
    unsafe { *can_compile_strings = allowed };
    true
}

#[expect(unsafe_code)]
/// <https://html.spec.whatwg.org/multipage/#notify-about-rejected-promises>
pub(crate) fn notify_about_rejected_promises(cx: &mut JSContext, global: &GlobalScope) {
    // Step 1. Let list be a clone of global's about-to-be-notified rejected promises list.
    let uncaught_rejections: Vec<TrustedPromise> = {
        global
            .get_uncaught_rejections()
            .borrow()
            .iter()
            .map(|promise| {
                let promise =
                    Promise::new_with_js_promise(cx, unsafe { Handle::from_raw(promise.handle()) });

                TrustedPromise::from(&promise)
            })
            .collect()
    };
    global.get_uncaught_rejections().safe_borrow_mut(cx).clear();

    // Step 2. If list is empty, then return.
    if uncaught_rejections.is_empty() {
        return;
    }

    // Step 3. Empty global's about-to-be-notified rejected promises list.
    // NOTE: We did this as part of Step 1. using the "drain(..)" call.

    // Step 4. Queue a global task on the DOM manipulation task source given global to run the following step:
    let target = Trusted::new(global.upcast::<EventTarget>());
    global.task_manager().dom_manipulation_task_source().queue(
        task!(unhandled_rejection_event: move |cx| {
            let target = target.root();

            // Step 4.1 For each promise p of list:
            for promise in uncaught_rejections {
                let promise = promise.root(cx);

                // 4.1.1 If p.[[PromiseIsHandled]] is true, then continue.
                if promise.get_promise_is_handled() {
                    continue;
                }

                // Step 4.1.2 Let notCanceled be the result of firing an event named unhandledrejection at global,
                // using PromiseRejectionEvent, with the cancelable attribute initialized to true,
                // the promise attribute initialized to p, and the reason attribute initialized to p.[[PromiseResult]].
                rooted!(&in(cx) let mut reason = UndefinedValue());
                unsafe {
                    JS_GetPromiseResult(promise.reflector().get_jsobject(), reason.handle_mut());
                }

                let event = PromiseRejectionEvent::new(
                    cx,
                    &target.global(),
                    atom!("unhandledrejection"),
                    EventBubbles::DoesNotBubble,
                    EventCancelable::Cancelable,
                    &promise,
                    reason.handle(),
                );
                let not_canceled = event.upcast::<Event>().fire(cx, &target);

                // Step 4.1.3 If notCanceled is true, then the user agent may report
                // p.[[PromiseResult]] to a developer console.
                if not_canceled {
                    let message = format!(
                        "Unhandled promise rejection: {}",
                        stringify_handle_value(cx, reason.handle())
                    );
                    Console::internal_error(cx, &target.global(), message);
                }

                // Step 4.1.4 If p.[[PromiseIsHandled]] is false, then append p to global's outstanding
                // rejected promises weak set.
                if !promise.get_promise_is_handled() {
                    target.global().add_consumed_rejection(promise.reflector().get_jsobject().into_handle());
                }
            }
        })
    );
}

/// Data that is sent to SpiderMonkey runtime callbacks as a pointer, which allows access
/// to the `Runtime` state.
#[derive(Default, JSTraceable, MallocSizeOf)]
struct RuntimeCallbackData {
    script_event_loop_sender: Option<ScriptEventLoopSender>,
    #[no_trace]
    #[ignore_malloc_size_of = "ScriptThread measures its own memory itself."]
    script_thread: Option<Weak<ScriptThread>>,
}

#[derive(JSTraceable, MallocSizeOf)]
pub(crate) struct Runtime {
    #[ignore_malloc_size_of = "Type from mozjs"]
    rt: RustRuntime,
    job_queue: JobQueue,
    /// The data that is set on the SpiderMonkey runtime callbacks as a pointer.
    runtime_callback_data: Box<RuntimeCallbackData>,
}

impl Runtime {
    /// Create a new runtime, optionally with the given [`SendableTaskSource`] for networking.
    ///
    /// # Safety
    ///
    /// If panicking does not abort the program, any threads with child runtimes will continue
    /// executing after the thread with the parent runtime panics, but they will be in an
    /// invalid and undefined state.
    ///
    /// This, like many calls to SpiderMoney API, is unsafe.
    #[expect(unsafe_code)]
    pub(crate) fn new(main_thread_sender: Option<ScriptEventLoopSender>) -> Runtime {
        unsafe { Self::new_with_parent(None, main_thread_sender) }
    }

    #[allow(unsafe_code)]
    /// ## Safety
    /// - only one `JSContext` can exist on the thread at a time (see note in [JSContext::from_ptr])
    /// - the `JSContext` must not outlive the `Runtime`
    pub(crate) unsafe fn cx(&self) -> JSContext {
        unsafe { JSContext::from_ptr(RustRuntime::get().unwrap()) }
    }

    /// Create a new runtime, optionally with the given [`ParentRuntime`] and [`SendableTaskSource`]
    /// for networking.
    ///
    /// # Safety
    ///
    /// If panicking does not abort the program, any threads with child runtimes will continue
    /// executing after the thread with the parent runtime panics, but they will be in an
    /// invalid and undefined state.
    ///
    /// The `parent` pointer in the [`ParentRuntime`] argument must point to a valid object in memory.
    ///
    /// This, like many calls to the SpiderMoney API, is unsafe.
    #[expect(unsafe_code)]
    pub(crate) unsafe fn new_with_parent(
        parent: Option<ParentRuntime>,
        script_event_loop_sender: Option<ScriptEventLoopSender>,
    ) -> Runtime {
        let mut runtime = if let Some(parent) = parent {
            unsafe { RustRuntime::create_with_parent(parent) }
        } else {
            RustRuntime::new(current_js_engine_handle())
        };
        let cx = runtime.cx();

        let have_event_loop_sender = script_event_loop_sender.is_some();
        let runtime_callback_data = Box::new(RuntimeCallbackData {
            script_event_loop_sender,
            script_thread: None,
        });
        let runtime_callback_data = Box::into_raw(runtime_callback_data);

        unsafe {
            JS_AddExtraGCRootsTracer(
                cx,
                Some(trace_rust_roots),
                runtime_callback_data as *mut c_void,
            );

            JS_SetSecurityCallbacks(cx, &SECURITY_CALLBACKS);

            JS_InitDestroyPrincipalsCallback(cx, Some(principals::destroy_servo_jsprincipal));
            JS_InitReadPrincipalsCallback(cx, Some(principals::read_jsprincipal));

            // Needed for debug assertions about whether GC is running.
            if cfg!(debug_assertions) {
                JS_SetGCCallback(cx, Some(debug_gc_callback), ptr::null_mut());
            }

            if opts::get()
                .debug
                .is_enabled(DiagnosticsLoggingOption::GcProfile)
            {
                SetGCSliceCallback(cx, Some(gc_slice_callback));
            }
        }

        unsafe extern "C" fn empty_wrapper_callback(_: *mut RawJSContext, _: HandleObject) -> bool {
            true
        }
        unsafe extern "C" fn empty_has_released_callback(_: HandleObject) -> bool {
            // fixme: return true when the Drop impl for a DOM object has been invoked
            false
        }

        unsafe {
            SetDOMCallbacks(cx, &DOM_CALLBACKS);
            SetPreserveWrapperCallbacks(
                cx,
                Some(empty_wrapper_callback),
                Some(empty_has_released_callback),
            );
        }

        unsafe extern "C" fn dispatch_to_event_loop(
            data: *mut c_void,
            dispatchable: *mut DispatchablePointer,
        ) -> bool {
            let runtime_callback_data: &RuntimeCallbackData =
                unsafe { &*(data as *mut RuntimeCallbackData) };
            let Some(script_event_loop_sender) =
                runtime_callback_data.script_event_loop_sender.as_ref()
            else {
                return false;
            };

            let runnable = Runnable(dispatchable);
            let task = task!(dispatch_to_event_loop_message: move |cx| {
                runnable.run(cx, Dispatchable_MaybeShuttingDown::NotShuttingDown);
            });

            script_event_loop_sender
                .send(CommonScriptMsg::Task(
                    ScriptThreadEventCategory::NetworkEvent,
                    Box::new(task),
                    None, /* pipeline_id */
                    TaskSourceName::Networking,
                ))
                .is_ok()
        }

        if have_event_loop_sender {
            unsafe {
                SetUpEventLoopDispatch(
                    cx,
                    Some(dispatch_to_event_loop),
                    None,
                    None,
                    runtime_callback_data as *mut c_void,
                );
            }
        }

        unsafe {
            InitConsumeStreamCallback(cx, Some(consume_stream), Some(report_stream_error));
        }

        let cx_opts;
        let job_queue;
        unsafe {
            let cx = runtime.cx();
            job_queue = JobQueue::new();
            job_queue.set_on_context(cx);
            SetPromiseRejectionTrackerCallback(
                cx,
                Some(promise_rejection_tracker),
                ptr::null_mut(),
            );

            RegisterScriptEnvironmentPreparer(
                cx.raw_cx(),
                Some(invoke_script_environment_preparer),
            );

            EnsureModuleHooksInitialized(runtime.rt());

            let cx = runtime.cx();

            set_gc_zeal_options(cx.raw_cx());

            // Enable or disable the JITs.
            cx_opts = &mut *ContextOptionsRef(cx);
            JS_SetGlobalJitCompilerOption(
                cx,
                JSJitCompilerOption::JSJITCOMPILER_BASELINE_INTERPRETER_ENABLE,
                pref!(js_baseline_interpreter_enabled) as u32,
            );
            JS_SetGlobalJitCompilerOption(
                cx,
                JSJitCompilerOption::JSJITCOMPILER_BASELINE_ENABLE,
                pref!(js_baseline_jit_enabled) as u32,
            );
            JS_SetGlobalJitCompilerOption(
                cx,
                JSJitCompilerOption::JSJITCOMPILER_ION_ENABLE,
                pref!(js_ion_enabled) as u32,
            );
        }
        cx_opts.compileOptions_.asmJSOption_ = if pref!(js_asmjs_enabled) {
            AsmJSOption::Enabled
        } else {
            AsmJSOption::DisabledByAsmJSPref
        };
        let wasm_enabled = pref!(js_wasm_enabled);
        cx_opts.set_wasm_(wasm_enabled);
        if wasm_enabled {
            // If WASM is enabled without setting the buildIdOp,
            // initializing a module will report an out of memory error.
            // https://dxr.mozilla.org/mozilla-central/source/js/src/wasm/WasmTypes.cpp#458
            unsafe { SetProcessBuildIdOp(Some(servo_build_id)) };
        }
        cx_opts.set_wasmBaseline_(pref!(js_wasm_baseline_enabled));
        cx_opts.set_wasmIon_(pref!(js_wasm_ion_enabled));

        unsafe {
            let cx = runtime.cx();
            // TODO: handle js.throw_on_asmjs_validation_failure (needs new Spidermonkey)
            JS_SetGlobalJitCompilerOption(
                cx,
                JSJitCompilerOption::JSJITCOMPILER_NATIVE_REGEXP_ENABLE,
                pref!(js_native_regex_enabled) as u32,
            );
            JS_SetOffthreadIonCompilationEnabled(cx, pref!(js_offthread_compilation_enabled));
            JS_SetGlobalJitCompilerOption(
                cx,
                JSJitCompilerOption::JSJITCOMPILER_BASELINE_WARMUP_TRIGGER,
                if pref!(js_baseline_jit_unsafe_eager_compilation_enabled) {
                    0
                } else {
                    u32::MAX
                },
            );
            JS_SetGlobalJitCompilerOption(
                cx,
                JSJitCompilerOption::JSJITCOMPILER_ION_NORMAL_WARMUP_TRIGGER,
                if pref!(js_ion_unsafe_eager_compilation_enabled) {
                    0
                } else {
                    u32::MAX
                },
            );
            // TODO: handle js.discard_system_source.enabled
            // TODO: handle js.asyncstack.enabled (needs new Spidermonkey)
            // TODO: handle js.throw_on_debugee_would_run (needs new Spidermonkey)
            // TODO: handle js.dump_stack_on_debugee_would_run (needs new Spidermonkey)
            // TODO: handle js.shared_memory.enabled
            JS_SetGCParameter(
                cx,
                JSGCParamKey::JSGC_MAX_BYTES,
                in_range(pref!(js_mem_max), 1, 0x100)
                    .map(|val| (val * 1024 * 1024) as u32)
                    .unwrap_or(u32::MAX),
            );

            // Pre-barriers aren't implemented correctly at the moment, so this preference
            // defaults to false.
            JS_SetGCParameter(
                cx,
                JSGCParamKey::JSGC_INCREMENTAL_GC_ENABLED,
                pref!(js_mem_gc_incremental_enabled) as u32,
            );

            JS_SetGCParameter(
                cx,
                JSGCParamKey::JSGC_PER_ZONE_GC_ENABLED,
                pref!(js_mem_gc_per_zone_enabled) as u32,
            );
            if let Some(val) = in_range(pref!(js_mem_gc_incremental_slice_ms), 0, 100_000) {
                JS_SetGCParameter(cx, JSGCParamKey::JSGC_SLICE_TIME_BUDGET_MS, val as u32);
            }
            JS_SetGCParameter(
                cx,
                JSGCParamKey::JSGC_COMPACTING_ENABLED,
                pref!(js_mem_gc_compacting_enabled) as u32,
            );

            if let Some(val) = in_range(pref!(js_mem_gc_high_frequency_time_limit_ms), 0, 10_000) {
                JS_SetGCParameter(cx, JSGCParamKey::JSGC_HIGH_FREQUENCY_TIME_LIMIT, val as u32);
            }
            if let Some(val) = in_range(pref!(js_mem_gc_low_frequency_heap_growth), 0, 10_000) {
                JS_SetGCParameter(cx, JSGCParamKey::JSGC_LOW_FREQUENCY_HEAP_GROWTH, val as u32);
            }
            if let Some(val) = in_range(pref!(js_mem_gc_high_frequency_heap_growth_min), 0, 10_000)
            {
                JS_SetGCParameter(
                    cx,
                    JSGCParamKey::JSGC_HIGH_FREQUENCY_LARGE_HEAP_GROWTH,
                    val as u32,
                );
            }
            if let Some(val) = in_range(pref!(js_mem_gc_high_frequency_heap_growth_max), 0, 10_000)
            {
                JS_SetGCParameter(
                    cx,
                    JSGCParamKey::JSGC_HIGH_FREQUENCY_SMALL_HEAP_GROWTH,
                    val as u32,
                );
            }
            if let Some(val) = in_range(pref!(js_mem_gc_high_frequency_low_limit_mb), 0, 10_000) {
                JS_SetGCParameter(cx, JSGCParamKey::JSGC_SMALL_HEAP_SIZE_MAX, val as u32);
            }
            if let Some(val) = in_range(pref!(js_mem_gc_high_frequency_high_limit_mb), 0, 10_000) {
                JS_SetGCParameter(cx, JSGCParamKey::JSGC_LARGE_HEAP_SIZE_MIN, val as u32);
            }
            if let Some(val) = in_range(pref!(js_mem_gc_empty_chunk_count_min), 0, 10_000) {
                JS_SetGCParameter(cx, JSGCParamKey::JSGC_MIN_EMPTY_CHUNK_COUNT, val as u32);
            }
            if let Some(val) = in_range(pref!(js_mem_gc_malloc_threshold_base_mb), 0, 10_000) {
                JS_SetGCParameter(cx, JSGCParamKey::JSGC_MALLOC_THRESHOLD_BASE, val as u32);
            }
            if let Some(val) = in_range(pref!(js_mem_gc_urgent_threshold_mb), 0, 10_000) {
                JS_SetGCParameter(cx, JSGCParamKey::JSGC_URGENT_THRESHOLD_MB, val as u32);
            }
        }
        Runtime {
            rt: runtime,
            job_queue,
            runtime_callback_data: unsafe { Box::from_raw(runtime_callback_data) },
        }
    }

    pub(crate) fn set_script_thread(&mut self, script_thread: Weak<ScriptThread>) {
        self.runtime_callback_data
            .script_thread
            .replace(script_thread);
    }

    pub(crate) fn thread_safe_js_context(&self) -> ThreadSafeJSContext {
        self.rt.thread_safe_js_context()
    }
}

impl Drop for Runtime {
    fn drop(&mut self) {
        // Clear our main microtask_queue.
        job_queue_clear(self.rt.cx_no_gc());

        LivePromiseReferences::destruct();
        script_bindings::refcounted::LiveDOMReferences::destruct();
        mark_runtime_dead();
    }
}

impl Deref for Runtime {
    type Target = RustRuntime;
    fn deref(&self) -> &RustRuntime {
        &self.rt
    }
}

impl DerefMut for Runtime {
    fn deref_mut(&mut self) -> &mut RustRuntime {
        &mut self.rt
    }
}

fn in_range<T: PartialOrd + Copy>(val: T, min: T, max: T) -> Option<T> {
    if val < min || val >= max {
        None
    } else {
        Some(val)
    }
}

thread_local!(static MALLOC_SIZE_OF_OPS: Cell<*mut MallocSizeOfOps> = const { Cell::new(ptr::null_mut()) });

#[derive(Default)]
struct InterfaceSizeData {
    /// How many live instances of this interface exist.
    count: usize,
    /// The total number of bytes allocated for instances of this interface.
    bytes: usize,
}

struct GlobalSizeData {
    /// The URL associated with this global.
    url: ServoUrl,
    /// A map of WebIDL interface names to size information.
    interface_sizes: HashMap<&'static str, InterfaceSizeData>,
    /// Is this global considered dead?
    is_zombie: bool,
}

#[derive(Default)]
/// A map of globals to size information for those globals.
/// The key is the global's JS reflector pointer as an integer.
pub(crate) struct PerGlobalInterfaceSizes(HashMap<usize, GlobalSizeData>);

thread_local!(
    static DOM_OBJECT_SIZES: LazyCell<RefCell<PerGlobalInterfaceSizes>> = const {
        LazyCell::new(Default::default)
    }
);

#[expect(unsafe_code)]
unsafe extern "C" fn get_size(obj: *mut JSObject) -> usize {
    let ops = MALLOC_SIZE_OF_OPS.get();
    ALREADY_COMPUTED_OBJECTS.with(|objects| {
        let ignored = objects.borrow();
        DOM_OBJECT_SIZES.with(|dom_sizes| {
            let mut per_global_interface_sizes = dom_sizes.borrow_mut();
            compute_size(
                obj,
                unsafe { &mut *ops },
                &ignored,
                Some(&mut per_global_interface_sizes),
            )
        })
    })
}

thread_local!(static GC_CYCLE_START: Cell<Option<Instant>> = const { Cell::new(None) });
thread_local!(static GC_SLICE_START: Cell<Option<Instant>> = const { Cell::new(None) });

#[expect(unsafe_code)]
unsafe extern "C" fn gc_slice_callback(
    _cx: *mut RawJSContext,
    progress: GCProgress,
    desc: *const GCDescription,
) {
    match progress {
        GCProgress::GC_CYCLE_BEGIN => GC_CYCLE_START.with(|start| {
            start.set(Some(Instant::now()));
            println!("GC cycle began");
        }),
        GCProgress::GC_SLICE_BEGIN => GC_SLICE_START.with(|start| {
            start.set(Some(Instant::now()));
            println!("GC slice began");
        }),
        GCProgress::GC_SLICE_END => GC_SLICE_START.with(|start| {
            let duration = start.get().unwrap().elapsed();
            start.set(None);
            println!("GC slice ended: duration={:?}", duration);
        }),
        GCProgress::GC_CYCLE_END => GC_CYCLE_START.with(|start| {
            let duration = start.get().unwrap().elapsed();
            start.set(None);
            println!("GC cycle ended: duration={:?}", duration);
        }),
    };
    if !desc.is_null() {
        let desc: &GCDescription = unsafe { &*desc };
        let options = match desc.options_ {
            GCOptions::Normal => "Normal",
            GCOptions::Shrink => "Shrink",
            GCOptions::Shutdown => "Shutdown",
        };
        println!("  isZone={}, options={}", desc.isZone_, options);
    }
    let _ = stdout().flush();
}

#[expect(unsafe_code)]
unsafe extern "C" fn debug_gc_callback(
    _cx: *mut RawJSContext,
    status: JSGCStatus,
    _reason: GCReason,
    _data: *mut os::raw::c_void,
) {
    match status {
        JSGCStatus::JSGC_BEGIN => thread_state::enter(ThreadState::IN_GC),
        JSGCStatus::JSGC_END => thread_state::exit(ThreadState::IN_GC),
    }
}

#[expect(unsafe_code)]
unsafe extern "C" fn trace_rust_roots(tr: *mut JSTracer, data: *mut os::raw::c_void) {
    if !runtime_is_alive() {
        return;
    }
    trace!("starting custom root handler");

    let runtime_callback_data = unsafe { &*(data as *const RuntimeCallbackData) };
    if let Some(script_thread) = runtime_callback_data
        .script_thread
        .as_ref()
        .and_then(Weak::upgrade)
    {
        trace!("tracing fields of ScriptThread");
        unsafe { script_thread.trace(tr) };
    };

    unsafe {
        trace_roots(tr);
        trace_refcounted_objects(tr);
        settings_stack::trace(tr);
    }
    trace!("done custom root handler");
}

#[expect(unsafe_code)]
unsafe extern "C" fn servo_build_id(build_id: *mut BuildIdCharVector) -> bool {
    let servo_id = b"Servo\0";
    unsafe { SetBuildId(build_id, servo_id[0] as *const c_char, servo_id.len()) }
}

#[expect(unsafe_code)]
#[cfg(feature = "debugmozjs")]
unsafe fn set_gc_zeal_options(cx: *mut RawJSContext) {
    use js::jsapi::SetGCZeal;

    let level = match pref!(js_mem_gc_zeal_level) {
        level @ 0..=14 => level as u8,
        _ => return,
    };
    let frequency = match pref!(js_mem_gc_zeal_frequency) {
        frequency if frequency >= 0 => frequency as u32,
        // https://searchfox.org/mozilla-esr128/source/js/public/GCAPI.h#1392
        _ => 5000,
    };
    unsafe {
        SetGCZeal(cx, level, frequency);
    }
}

#[expect(unsafe_code)]
#[cfg(not(feature = "debugmozjs"))]
unsafe fn set_gc_zeal_options(_: *mut RawJSContext) {}

thread_local!(static ALREADY_COMPUTED_OBJECTS: LazyCell<RefCell<HashSet<*const JSObject>>> = const {
    LazyCell::new(Default::default)
});

#[expect(unsafe_code)]
pub(crate) fn compute_size(
    obj: *mut JSObject,
    ops: &mut MallocSizeOfOps,
    ignored: &HashSet<*const JSObject>,
    per_global_interface_sizes: Option<&mut PerGlobalInterfaceSizes>,
) -> usize {
    if ignored.contains(&(obj as *const JSObject)) {
        return 0;
    }

    match unsafe { get_dom_class(obj) } {
        Ok(v) => {
            let dom_object = unsafe { private_from_object(obj) as *const c_void };

            if dom_object.is_null() {
                return 0;
            }
            let size = unsafe { (v.malloc_size_of)(&mut *ops, dom_object) };

            let Some(per_global_interface_sizes) = per_global_interface_sizes else {
                return size;
            };

            let global = unsafe { js::jsapi::GetNonCCWObjectGlobal(obj) };
            let interface = v.interface_chain[v.depth as usize];
            let interface_size = per_global_interface_sizes
                .0
                .entry(global as usize)
                .or_insert_with(|| {
                    let global = unsafe { GlobalScope::from_object(obj) };
                    GlobalSizeData {
                        url: global.get_url(),
                        interface_sizes: HashMap::new(),
                        is_zombie: global
                            .downcast::<Window>()
                            .is_some_and(|window| !window.is_alive()),
                    }
                })
                .interface_sizes
                .entry(interface.into())
                .or_default();
            interface_size.count += 1;
            interface_size.bytes += size;
            // Always report a size of zero, since we report this value
            // in a separate tree from the main JS heap.
            0
        },
        Err(_e) => 0,
    }
}

#[expect(unsafe_code)]
pub(crate) fn get_reports(
    cx: &mut JSContext,
    path_seg: String,
    ops: &mut MallocSizeOfOps,
    already_computed_objects: HashSet<*const JSObject>,
) -> Vec<Report> {
    MALLOC_SIZE_OF_OPS.with(|ops_tls| ops_tls.set(ops));
    ALREADY_COMPUTED_OBJECTS.with(|objects| {
        *objects.borrow_mut() = already_computed_objects;
    });

    let stats = unsafe {
        let mut stats = ::std::mem::zeroed();
        if !CollectServoSizes(cx, &mut stats, Some(get_size)) {
            return vec![];
        }
        stats
    };
    MALLOC_SIZE_OF_OPS.with(|ops| ops.set(ptr::null_mut()));
    ALREADY_COMPUTED_OBJECTS.with(|objects| {
        let mut objects = objects.borrow_mut();
        objects.clear();
        objects.shrink_to_fit();
    });

    let mut reports = vec![];
    let mut report = |mut path_suffix, kind, size| {
        let mut path = path![path_seg, "js"];
        path.append(&mut path_suffix);
        reports.push(Report { path, kind, size })
    };

    DOM_OBJECT_SIZES.with(|sizes| {
        let mut sizes = sizes.borrow_mut();
        let mut known_globals = HashMap::new();
        for global_size_data in sizes.0.values() {
            let url = global_size_data.url.as_str();
            let suffix = if global_size_data.is_zombie {
                "-zombie"
            } else {
                ""
            };
            let index = known_globals.entry(url).or_insert(0);
            *index += 1;
            for (interface, interface_data) in &global_size_data.interface_sizes {
                report(
                    path![
                        "dom",
                        "out-of-tree",
                        format!("url({url}){suffix}-{}", *index),
                        format!("{interface} [{}]", interface_data.count)
                    ],
                    ReportKind::ExplicitJemallocHeapSize,
                    interface_data.bytes,
                );
            }
        }
        sizes.0.clear();
    });

    // A note about possibly confusing terminology: the JS GC "heap" is allocated via
    // mmap/VirtualAlloc, which means it's not on the malloc "heap", so we use
    // `ExplicitNonHeapSize` as its kind.
    report(
        path!["gc-heap", "used"],
        ReportKind::ExplicitNonHeapSize,
        stats.gcHeapUsed,
    );

    report(
        path!["gc-heap", "unused"],
        ReportKind::ExplicitNonHeapSize,
        stats.gcHeapUnused,
    );

    report(
        path!["gc-heap", "admin"],
        ReportKind::ExplicitNonHeapSize,
        stats.gcHeapAdmin,
    );

    report(
        path!["gc-heap", "decommitted"],
        ReportKind::ExplicitNonHeapSize,
        stats.gcHeapDecommitted,
    );

    // SpiderMonkey uses the system heap, not jemalloc.
    report(
        path!["malloc-heap"],
        ReportKind::ExplicitSystemHeapSize,
        stats.mallocHeap,
    );

    report(
        path!["non-heap"],
        ReportKind::ExplicitNonHeapSize,
        stats.nonHeap,
    );
    reports
}

pub(crate) struct StreamConsumer(*mut JSStreamConsumer);

#[expect(unsafe_code)]
impl StreamConsumer {
    pub(crate) fn consume_chunk(&self, stream: &[u8]) -> bool {
        unsafe {
            let stream_ptr = stream.as_ptr();
            StreamConsumerConsumeChunk(self.0, stream_ptr, stream.len())
        }
    }

    pub(crate) fn stream_end(&self) {
        unsafe {
            StreamConsumerStreamEnd(self.0);
        }
    }

    pub(crate) fn stream_error(&self, error_code: usize) {
        unsafe {
            StreamConsumerStreamError(self.0, error_code);
        }
    }

    pub(crate) fn note_response_urls(
        &self,
        maybe_url: Option<String>,
        maybe_source_map_url: Option<String>,
    ) {
        unsafe {
            let maybe_url = maybe_url.map(|url| CString::new(url).unwrap());
            let maybe_source_map_url = maybe_source_map_url.map(|url| CString::new(url).unwrap());

            let maybe_url_param = match maybe_url.as_ref() {
                Some(url) => url.as_ptr(),
                None => ptr::null(),
            };
            let maybe_source_map_url_param = match maybe_source_map_url.as_ref() {
                Some(url) => url.as_ptr(),
                None => ptr::null(),
            };

            StreamConsumerNoteResponseURLs(self.0, maybe_url_param, maybe_source_map_url_param);
        }
    }
}

/// Implements the steps to compile webassembly response mentioned here
/// <https://webassembly.github.io/spec/web-api/#compile-a-potential-webassembly-response>
#[expect(unsafe_code)]
unsafe extern "C" fn consume_stream(
    cx: *mut RawJSContext,
    obj: HandleObject,
    _mime_type: MimeType,
    _consumer: *mut JSStreamConsumer,
) -> bool {
    let mut cx = unsafe {
        // SAFETY: We are in SM hook
        JSContext::from_ptr(NonNull::new(cx).expect("JSContext should not be null in SM hook"))
    };
    let cx = &mut cx;
    let mut realm = CurrentRealm::assert(cx);
    let global = GlobalScope::from_current_realm(&mut realm);

    // Step 2.1 Upon fulfillment of source, store the Response with value unwrappedSource.
    if let Ok(unwrapped_source) =
        unsafe { root_from_handleobject::<Response>(cx, RustHandleObject::from_raw(obj)) }
    {
        // Step 2.2 Let mimeType be the result of extracting a MIME type from response’s header list.
        let mimetype = unwrapped_source.Headers(cx).extract_mime_type();

        // Step 2.3 If mimeType is not `application/wasm`, return with a TypeError and abort these substeps.
        if !&mimetype[..].eq_ignore_ascii_case(b"application/wasm") {
            throw_dom_exception(
                cx,
                &global,
                Error::Type(c"Response has unsupported MIME type".to_owned()),
            );
            return false;
        }

        // Step 2.4 If response is not CORS-same-origin, return with a TypeError and abort these substeps.
        match unwrapped_source.Type() {
            DOMResponseType::Basic | DOMResponseType::Cors | DOMResponseType::Default => {},
            _ => {
                throw_dom_exception(
                    cx,
                    &global,
                    Error::Type(c"Response.type must be 'basic', 'cors' or 'default'".to_owned()),
                );
                return false;
            },
        }

        // Step 2.5 If response’s status is not an ok status, return with a TypeError and abort these substeps.
        if !unwrapped_source.Ok() {
            throw_dom_exception(
                cx,
                &global,
                Error::Type(c"Response does not have ok status".to_owned()),
            );
            return false;
        }

        // Step 2.6.1 If response body is locked, return with a TypeError and abort these substeps.
        if unwrapped_source.is_locked() {
            throw_dom_exception(
                cx,
                &global,
                Error::Type(c"There was an error consuming the Response".to_owned()),
            );
            return false;
        }

        // Step 2.6.2 If response body is alreaady consumed, return with a TypeError and abort these substeps.
        if unwrapped_source.is_disturbed() {
            throw_dom_exception(
                cx,
                &global,
                Error::Type(c"Response already consumed".to_owned()),
            );
            return false;
        }
        unwrapped_source.set_stream_consumer(Some(StreamConsumer(_consumer)));
    } else {
        // Step 3 Upon rejection of source, return with reason.
        throw_dom_exception(
            cx,
            &global,
            Error::Type(c"expected Response or Promise resolving to Response".to_owned()),
        );
        return false;
    }
    true
}

#[expect(unsafe_code)]
unsafe extern "C" fn report_stream_error(_cx: *mut RawJSContext, error_code: usize) {
    error!("Error initializing StreamConsumer: {:?}", unsafe {
        RUST_js_GetErrorMessage(ptr::null_mut(), error_code as u32)
    });
}

#[expect(unsafe_code)]
unsafe extern "C" fn invoke_script_environment_preparer(
    global: HandleObject,
    closure: *mut ScriptEnvironmentPreparer_Closure,
) {
    // SAFETY: always safe from a JS engine hook.
    let mut cx = unsafe { temp_cx() };
    let global = unsafe { GlobalScope::from_object(global.get()) };
    let mut realm = enter_auto_realm(&mut cx, &*global);
    let cx = &mut realm.current_realm();

    run_a_script::<DomTypeHolder, _, _>(cx, &global, |cx| {
        if unsafe { !RunScriptEnvironmentPreparerClosure(cx.raw_cx(), closure) } {
            report_pending_exception(cx);
        };
    });
}

pub(crate) struct Runnable(*mut DispatchablePointer);

#[expect(unsafe_code)]
unsafe impl Sync for Runnable {}
#[expect(unsafe_code)]
unsafe impl Send for Runnable {}

#[expect(unsafe_code)]
impl Runnable {
    fn run(&self, cx: &mut JSContext, maybe_shutting_down: Dispatchable_MaybeShuttingDown) {
        unsafe {
            DispatchableRun(cx, self.0, maybe_shutting_down);
        }
    }
}

/// `introductionType` values in SpiderMonkey TransitiveCompileOptions.
///
/// Value definitions are based on the SpiderMonkey Debugger API docs:
/// <https://firefox-source-docs.mozilla.org/js/Debugger/Debugger.Source.html#introductiontype>
// TODO: squish `scriptElement` <https://searchfox.org/mozilla-central/rev/202069c4c5113a1a9052d84fa4679d4c1b22113e/devtools/server/actors/source.js#199-201>
pub(crate) struct IntroductionType;
impl IntroductionType {
    /// `introductionType` for code passed to `eval`.
    pub const EVAL: &CStr = c"eval";
    pub const EVAL_STR: &str = "eval";

    /// `introductionType` for code evaluated by debugger.
    /// This includes code run via the devtools repl, even if the thread is not paused.
    pub const DEBUGGER_EVAL: &CStr = c"debugger eval";
    pub const DEBUGGER_EVAL_STR: &str = "debugger eval";

    /// `introductionType` for code passed to the `Function` constructor.
    pub const FUNCTION: &CStr = c"Function";
    pub const FUNCTION_STR: &str = "Function";

    /// `introductionType` for code loaded by worklet.
    pub const WORKLET: &CStr = c"Worklet";
    pub const WORKLET_STR: &str = "Worklet";

    /// `introductionType` for code assigned to DOM elements’ event handler IDL attributes as a string.
    pub const EVENT_HANDLER: &CStr = c"eventHandler";
    pub const EVENT_HANDLER_STR: &str = "eventHandler";

    /// `introductionType` for code belonging to `<script src="file.js">` elements.
    /// This includes `<script type="module" src="...">`.
    pub const SRC_SCRIPT: &CStr = c"srcScript";
    pub const SRC_SCRIPT_STR: &str = "srcScript";

    /// `introductionType` for code belonging to `<script>code;</script>` elements.
    /// This includes `<script type="module" src="...">`.
    pub const INLINE_SCRIPT: &CStr = c"inlineScript";
    pub const INLINE_SCRIPT_STR: &str = "inlineScript";

    /// `introductionType` for code belonging to scripts that *would* be `"inlineScript"` except that they were not
    /// part of the initial file itself.
    /// For example, scripts created via:
    /// - `document.write("<script>code;</script>")`
    /// - `var s = document.createElement("script"); s.text = "code";`
    pub const INJECTED_SCRIPT: &CStr = c"injectedScript";
    pub const INJECTED_SCRIPT_STR: &str = "injectedScript";

    /// `introductionType` for code that was loaded indirectly by being imported by another script
    /// using ESM static or dynamic imports.
    pub const IMPORTED_MODULE: &CStr = c"importedModule";
    pub const IMPORTED_MODULE_STR: &str = "importedModule";

    /// `introductionType` for code presented in `javascript:` URLs.
    pub const JAVASCRIPT_URL: &CStr = c"javascriptURL";
    pub const JAVASCRIPT_URL_STR: &str = "javascriptURL";

    /// `introductionType` for code passed to `setTimeout`/`setInterval` as a string.
    pub const DOM_TIMER: &CStr = c"domTimer";
    pub const DOM_TIMER_STR: &str = "domTimer";

    /// `introductionType` for web workers.
    /// FIXME: only documented in older(?) devtools user docs
    /// <https://firefox-source-docs.mozilla.org/devtools-user/debugger-api/debugger.source/index.html>
    pub const WORKER: &CStr = c"Worker";
    pub const WORKER_STR: &str = "Worker";
}