script: Create a debugger script for the SpiderMonkey Debugger API (#38331)

to use the [SpiderMonkey Debugger
API](https://firefox-source-docs.mozilla.org/js/Debugger/), we need to
call it from an internal debugger script that we will supply. this
script must run in the same runtime as the debuggee(s), but in a
separate
[compartment](https://udn.realityripple.com/docs/Mozilla/Projects/SpiderMonkey/Compartments)
([more
details](https://hacks.mozilla.org/2020/03/future-proofing-firefoxs-javascript-debugger-implementation/)).

this patch defines a new DebuggerGlobalScope type and a new debugger
script resource. when creating each script thread, we create a debugger
global, load the debugger script from resources/debugger.js, and run
that script in the global to initialise the Debugger API.

subsequent patches will use the debugger script as an RPC mechanism for
the Debugger API.

Testing: no testable effects yet, but will be used in #37667
Fixes: part of #36027

---------

Signed-off-by: Delan Azabani <dazabani@igalia.com>
Co-authored-by: atbrakhi <atbrakhi@igalia.com>

components/script/dom/debuggerglobalscope.rs

@@ -0,0 +1,122 @@
+/* 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/. */
+
+use base::id::PipelineId;
+use constellation_traits::ScriptToConstellationChan;
+use crossbeam_channel::Sender;
+use devtools_traits::ScriptToDevtoolsControlMsg;
+use dom_struct::dom_struct;
+use embedder_traits::resources::{self, Resource};
+use ipc_channel::ipc::IpcSender;
+use js::jsval::UndefinedValue;
+use js::rust::Runtime;
+use js::rust::wrappers::JS_DefineDebuggerObject;
+use net_traits::ResourceThreads;
+use profile_traits::{mem, time};
+use script_bindings::realms::InRealm;
+use script_bindings::reflector::DomObject;
+use servo_url::{ImmutableOrigin, MutableOrigin, ServoUrl};
+
+use crate::dom::bindings::codegen::Bindings::DebuggerGlobalScopeBinding;
+use crate::dom::bindings::error::report_pending_exception;
+use crate::dom::bindings::inheritance::Castable;
+use crate::dom::bindings::root::DomRoot;
+use crate::dom::bindings::trace::CustomTraceable;
+use crate::dom::bindings::utils::define_all_exposed_interfaces;
+use crate::dom::globalscope::GlobalScope;
+#[cfg(feature = "testbinding")]
+#[cfg(feature = "webgpu")]
+use crate::dom::webgpu::identityhub::IdentityHub;
+use crate::messaging::MainThreadScriptMsg;
+use crate::realms::enter_realm;
+use crate::script_module::ScriptFetchOptions;
+use crate::script_runtime::{CanGc, JSContext};
+
+#[dom_struct]
+/// Global scope for interacting with the devtools Debugger API.
+///
+/// <https://firefox-source-docs.mozilla.org/js/Debugger/>
+pub(crate) struct DebuggerGlobalScope {
+    global_scope: GlobalScope,
+    script_chan: Sender<MainThreadScriptMsg>,
+}
+
+impl DebuggerGlobalScope {
+    /// Create a new heap-allocated `DebuggerGlobalScope`.
+    #[allow(unsafe_code, clippy::too_many_arguments)]
+    pub(crate) fn new(
+        runtime: &Runtime,
+        script_chan: Sender<MainThreadScriptMsg>,
+        devtools_chan: Option<IpcSender<ScriptToDevtoolsControlMsg>>,
+        mem_profiler_chan: mem::ProfilerChan,
+        time_profiler_chan: time::ProfilerChan,
+        script_to_constellation_chan: ScriptToConstellationChan,
+        resource_threads: ResourceThreads,
+        #[cfg(feature = "webgpu")] gpu_id_hub: std::sync::Arc<IdentityHub>,
+        can_gc: CanGc,
+    ) -> DomRoot<Self> {
+        let global = Box::new(Self {
+            global_scope: GlobalScope::new_inherited(
+                PipelineId::new(),
+                devtools_chan,
+                mem_profiler_chan,
+                time_profiler_chan,
+                script_to_constellation_chan,
+                resource_threads,
+                MutableOrigin::new(ImmutableOrigin::new_opaque()),
+                ServoUrl::parse_with_base(None, "about:internal/debugger")
+                    .expect("Guaranteed by argument"),
+                None,
+                Default::default(),
+                #[cfg(feature = "webgpu")]
+                gpu_id_hub,
+                None,
+                false,
+            ),
+            script_chan,
+        });
+        let global = unsafe {
+            DebuggerGlobalScopeBinding::Wrap::<crate::DomTypeHolder>(
+                JSContext::from_ptr(runtime.cx()),
+                global,
+            )
+        };
+
+        let realm = enter_realm(&*global);
+        define_all_exposed_interfaces(global.upcast(), InRealm::entered(&realm), can_gc);
+        assert!(unsafe {
+            // Invariants: `cx` must be a non-null, valid JSContext pointer,
+            // and `obj` must be a handle to a JS global object.
+            JS_DefineDebuggerObject(
+                *Self::get_cx(),
+                global.global_scope.reflector().get_jsobject(),
+            )
+        });
+
+        global
+    }
+
+    /// Get the JS context.
+    pub(crate) fn get_cx() -> JSContext {
+        GlobalScope::get_cx()
+    }
+
+    fn evaluate_js(&self, script: &str, can_gc: CanGc) -> bool {
+        rooted!(in (*Self::get_cx()) let mut rval = UndefinedValue());
+        self.global_scope.evaluate_js_on_global_with_result(
+            script,
+            rval.handle_mut(),
+            ScriptFetchOptions::default_classic_script(&self.global_scope),
+            self.global_scope.api_base_url(),
+            can_gc,
+        )
+    }
+
+    pub(crate) fn execute(&self, can_gc: CanGc) {
+        if !self.evaluate_js(&resources::read_string(Resource::DebuggerJS), can_gc) {
+            let ar = enter_realm(self);
+            report_pending_exception(Self::get_cx(), true, InRealm::Entered(&ar), can_gc);
+        }
+    }
+}

components/script/dom/globalscope.rs

@@ -114,7 +114,7 @@ use crate::dom::reportingobserver::ReportingObserver;
 use crate::dom::serviceworker::ServiceWorker;
 use crate::dom::serviceworkerregistration::ServiceWorkerRegistration;
 use crate::dom::trustedtypepolicyfactory::TrustedTypePolicyFactory;
-use crate::dom::types::MessageEvent;
+use crate::dom::types::{DebuggerGlobalScope, MessageEvent};
 use crate::dom::underlyingsourcecontainer::UnderlyingSourceType;
 #[cfg(feature = "webgpu")]
 use crate::dom::webgpu::gpudevice::GPUDevice;
@@ -2530,6 +2530,9 @@ impl GlobalScope {
             // https://drafts.css-houdini.org/worklets/#script-settings-for-worklets
             return worklet.base_url();
         }
+        if let Some(_debugger_global) = self.downcast::<DebuggerGlobalScope>() {
+            return self.creation_url.clone();
+        }
         unreachable!();
     }
 
@@ -2545,6 +2548,9 @@ impl GlobalScope {
             // TODO: is this the right URL to return?
             return worklet.base_url();
         }
+        if let Some(_debugger_global) = self.downcast::<DebuggerGlobalScope>() {
+            return self.creation_url.clone();
+        }
         unreachable!();
     }
 

components/script/dom/mod.rs

@@ -289,6 +289,7 @@ pub(crate) mod customevent;
 pub(crate) mod datatransfer;
 pub(crate) mod datatransferitem;
 pub(crate) mod datatransferitemlist;
+pub(crate) mod debuggerglobalscope;
 pub(crate) mod dedicatedworkerglobalscope;
 pub(crate) mod defaultteereadrequest;
 pub(crate) mod defaultteeunderlyingsource;

components/script/script_thread.rs

@@ -133,6 +133,7 @@ use crate::dom::htmlslotelement::HTMLSlotElement;
 use crate::dom::mutationobserver::MutationObserver;
 use crate::dom::node::{Node, NodeTraits, ShadowIncluding};
 use crate::dom::servoparser::{ParserContext, ServoParser};
+use crate::dom::types::DebuggerGlobalScope;
 #[cfg(feature = "webgpu")]
 use crate::dom::webgpu::identityhub::IdentityHub;
 use crate::dom::window::Window;
@@ -348,6 +349,8 @@ pub struct ScriptThread {
     /// itself is managing animations the the timer fired triggering a [`ScriptThread`]-based
     /// animation tick.
     has_pending_animation_tick: Arc<AtomicBool>,
+
+    debugger_global: Dom<DebuggerGlobalScope>,
 }
 
 struct BHMExitSignal {
@@ -928,6 +931,30 @@ impl ScriptThread {
             content_process_shutdown_sender: state.content_process_shutdown_sender,
         };
 
+        let microtask_queue = runtime.microtask_queue.clone();
+        let js_runtime = Rc::new(runtime);
+        #[cfg(feature = "webgpu")]
+        let gpu_id_hub = Arc::new(IdentityHub::default());
+
+        let pipeline_id = PipelineId::new();
+        let script_to_constellation_chan = ScriptToConstellationChan {
+            sender: senders.pipeline_to_constellation_sender.clone(),
+            pipeline_id,
+        };
+        let debugger_global = DebuggerGlobalScope::new(
+            &js_runtime.clone(),
+            senders.self_sender.clone(),
+            senders.devtools_server_sender.clone(),
+            senders.memory_profiler_sender.clone(),
+            senders.time_profiler_sender.clone(),
+            script_to_constellation_chan,
+            state.resource_threads.clone(),
+            #[cfg(feature = "webgpu")]
+            gpu_id_hub.clone(),
+            CanGc::note(),
+        );
+        debugger_global.execute(CanGc::note());
+
         ScriptThread {
             documents: DomRefCell::new(DocumentCollection::default()),
             last_render_opportunity_time: Default::default(),
@@ -942,8 +969,8 @@ impl ScriptThread {
             background_hang_monitor,
             closing,
             timer_scheduler: Default::default(),
-            microtask_queue: runtime.microtask_queue.clone(),
-            js_runtime: Rc::new(runtime),
+            microtask_queue,
+            js_runtime,
             topmost_mouse_over_target: MutNullableDom::new(Default::default()),
             closed_pipelines: DomRefCell::new(HashSet::new()),
             mutation_observer_microtask_queued: Default::default(),
@@ -967,12 +994,13 @@ impl ScriptThread {
             pipeline_to_node_ids: Default::default(),
             is_user_interacting: Cell::new(false),
             #[cfg(feature = "webgpu")]
-            gpu_id_hub: Arc::new(IdentityHub::default()),
+            gpu_id_hub,
             inherited_secure_context: state.inherited_secure_context,
             layout_factory,
             relative_mouse_down_point: Cell::new(Point2D::zero()),
             scheduled_script_thread_animation_timer: Default::default(),
             has_pending_animation_tick: Arc::new(AtomicBool::new(false)),
+            debugger_global: debugger_global.as_traced(),
         }
     }