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);
+        }
+    }
+}