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Expose ScriptEnvironmentPreparer to Rust #598

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Expose ScriptEnvironmentPreparer to Rust #598

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19 changes: 19 additions & 0 deletions mozjs-sys/src/jsglue.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -173,6 +173,21 @@ class RustJobQueue : public JS::JobQueue {
}
};

struct RustEnvironmentPreparer : public js::ScriptEnvironmentPreparer {
JSContext* cx;
explicit RustEnvironmentPreparer(JSContext* cx) : cx(cx) {}
void invoke(JS::HandleObject global, Closure& closure) override {
MOZ_ASSERT(JS_IsGlobalObject(global));
MOZ_ASSERT(!JS_IsExceptionPending(cx));

JSAutoRealm ar(cx, global);
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This looks like you're modelling it off of the jsshell version, but I intend to use this to replicate https://searchfox.org/mozilla-central/rev/fcc0cfc7f5b1df957ae29f6b2ccfeb6df47b6be8/xpcom/base/CycleCollectedJSRuntime.cpp#2177 . Since AutoEntryScript is a Servo Rust type, can we make this class implement a hook for Rust code to invoke the closure instead?

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I intend to use this to replicate https://searchfox.org/mozilla-central/rev/fcc0cfc7f5b1df957ae29f6b2ccfeb6df47b6be8/xpcom/base/CycleCollectedJSRuntime.cpp#2177

can you elaborate on this? i’m not sure i follow, did you have existing plans to set up a ScriptEnvironmentPreparer for Servo?

Since AutoEntryScript is a Servo Rust type, can we make this class implement a hook for Rust code to invoke the closure instead?

yeah, that could work. would the idea be that RustEnvironmentPreparer::invoke() just passes the closure to Servo, which would enter the AutoEntryScript and call the closure?

also, what do we do with uncaught exceptions? the jsshell uses a thing called AutoReportException, but i’m not sure what the Servo counterpart is for that.

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can you elaborate on this? i’m not sure i follow, did you have existing plans to set up a ScriptEnvironmentPreparer for Servo?

I didn't know it existed until this PR, but now I want to replicate the way Gecko uses it.

yeah, that could work. would the idea be that RustEnvironmentPreparer::invoke() just passes the closure to Servo, which would enter the AutoEntryScript and call the closure

Yes.

also, what do we do with uncaught exceptions? the jsshell uses a thing called AutoReportException, but i’m not sure what the Servo counterpart is for that.

We have code that calls report_pending_exception in various places right now. Gecko uses AutoJsApi, which is another thing I want to replicate.

// TODO: AutoReportException are(cx);
if (!closure(cx)) {
return;
}
}
};

struct JSExternalStringCallbacksTraps {
void (*latin1Finalize)(const void* privateData, JS::Latin1Char* chars);
void (*utf16Finalize)(const void* privateData, char16_t* chars);
Expand Down Expand Up @@ -1106,6 +1121,10 @@ JS::JobQueue* CreateJobQueue(const JobQueueTraps* aTraps, const void* aQueue,

void DeleteJobQueue(JS::JobQueue* queue) { delete queue; }

void InitScriptEnvironmentPreparer(JSContext* cx) {
js::SetScriptEnvironmentPreparer(cx, new RustEnvironmentPreparer(cx));
}

JSExternalStringCallbacks* CreateJSExternalStringCallbacks(
const JSExternalStringCallbacksTraps* aTraps, void* privateData) {
return new RustJSExternalStringCallbacks(*aTraps, privateData);
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