Bug 1730426 - Start explicitly throwing uncatchable exceptions. r=jandem

Add Interrupt status to JS::ExceptionStatus and set it when intentionally
throwing an uncatchable exception. This is only a guideline for now, so avoid
excessive asserts for now.

Differential Revision: https://phabricator.services.mozilla.com/D125363

js/public/Exception.h

@@ -39,6 +39,12 @@ extern JS_PUBLIC_API void JS_SetPendingException(
     JSContext* cx, JS::HandleValue v,
     JS::ExceptionStackBehavior behavior = JS::ExceptionStackBehavior::Capture);
 
+// Indicate that we are intentionally raising an interrupt/uncatchable
+// exception. Returning false/nullptr without calling this will still be treated
+// as an interrupt, but in the future the implicit behaviour may no longer be
+// allowed.
+extern JS_PUBLIC_API void JS_SetPendingInterrupt(JSContext* cx);
+
 extern JS_PUBLIC_API void JS_ClearPendingException(JSContext* cx);
 
 /**
@@ -56,7 +62,9 @@ namespace JS {
 // When propagating an exception up the call stack, we store the underlying
 // reason on the JSContext as one of the following enum values.
 //
-// TODO: Track uncatchable exceptions explicitly.
+// NOTE: It is not yet a hard requirement for uncatchable exceptions to set
+//       status to Interrupt so rely on the last return value. If Interrupt is
+//       not set then the status will remain as None.
 enum class ExceptionStatus {
   // No expection status.
   None,
@@ -66,6 +74,12 @@ enum class ExceptionStatus {
   // non-error completion.
   ForcedReturn,
 
+  // An uncatchable exception that functions as an interrupt. This is used for
+  // watchdog mechanisms (like the slow-script notification) or the debugger
+  // API. It cannot be caught be JS catch blocks, but the debugger or event
+  // loops may still capture it.
+  Interrupt,
+
   // Throwing a (catchable) exception. Certain well-known exceptions are
   // explicitly tracked for convenience.
   Throwing,

js/src/builtin/TestingFunctions.cpp

@@ -3680,7 +3680,7 @@ static bool Terminate(JSContext* cx, unsigned arg, Value* vp) {
     fprintf(stderr, "terminate called\n");
   }
 
-  JS_ClearPendingException(cx);
+  cx->setInterrupting();
   return false;
 }
 

js/src/debugger/Debugger.cpp

@@ -300,7 +300,7 @@ static void PropagateForcedReturn(JSContext* cx, AbstractFramePtr frame,
       return false;
 
     case ResumeMode::Terminate:
-      cx->clearPendingException();
+      cx->setInterrupting();
       return false;
 
     case ResumeMode::Return:
@@ -1018,7 +1018,7 @@ NativeResumeMode DebugAPI::slowPathOnNativeCall(JSContext* cx,
       return NativeResumeMode::Abort;
 
     case ResumeMode::Terminate:
-      cx->clearPendingException();
+      cx->setInterrupting();
       return NativeResumeMode::Abort;
 
     case ResumeMode::Return:
@@ -1951,6 +1951,7 @@ Completion Completion::fromJSResult(JSContext* cx, bool ok, const Value& rv) {
   }
 
   if (!cx->isExceptionPending()) {
+    cx->clearInterrupt();
     return Completion(Terminate());
   }
 

js/src/jit/JitFrames.cpp

@@ -524,7 +524,7 @@ again:
     }
 
     // We may be propagating a forced return from a debugger hook function.
-    if (MOZ_UNLIKELY(cx->isPropagatingForcedReturn())) {
+    if (cx->isPropagatingForcedReturn()) {
       cx->clearPropagatingForcedReturn();
       frameOk = true;
     }

js/src/jsapi.cpp

@@ -3685,6 +3685,10 @@ JS_PUBLIC_API void JS_SetPendingException(JSContext* cx, HandleValue value,
   }
 }
 
+JS_PUBLIC_API void JS_SetPendingInterrupt(JSContext* cx) {
+  cx->setInterrupting();
+}
+
 JS_PUBLIC_API void JS_ClearPendingException(JSContext* cx) {
   AssertHeapIsIdle();
   cx->clearPendingException();

js/src/shell/js.cpp

@@ -2617,6 +2617,7 @@ static bool Evaluate(JSContext* cx, unsigned argc, Value* vp) {
                 ? JS_ExecuteScript(cx, script, args.rval())
                 : JS_ExecuteScript(cx, envChain, script, args.rval()))) {
         if (catchTermination && !JS_IsExceptionPending(cx)) {
+          cx->clearInterrupt();
           JSAutoRealm ar1(cx, callerGlobal);
           JSString* str = JS_NewStringCopyZ(cx, "terminated");
           if (!str) {
@@ -3147,6 +3148,8 @@ static bool Quit(JSContext* cx, unsigned argc, Value* vp) {
   js::StopDrainingJobQueue(cx);
   sc->exitCode = code;
   sc->quitting = true;
+
+  cx->setInterrupting();
   return false;
 }
 

js/src/vm/Interpreter.cpp

@@ -1220,7 +1220,7 @@ again:
     UnwindIteratorsForUncatchableException(cx, regs);
 
     // We may be propagating a forced return from a debugger hook function.
-    if (MOZ_UNLIKELY(cx->isPropagatingForcedReturn())) {
+    if (cx->isPropagatingForcedReturn()) {
       cx->clearPropagatingForcedReturn();
       ok = true;
     }

js/src/vm/JSContext.cpp

@@ -837,6 +837,7 @@ void InternalJobQueue::runJobs(JSContext* cx) {
         if (!JS::Call(cx, UndefinedHandleValue, job, args, &rval)) {
           // Nothing we can do about uncatchable exceptions.
           if (!cx->isExceptionPending()) {
+            cx->clearInterrupt();
             continue;
           }
           RootedValue exn(cx);

js/src/vm/JSContext.h

@@ -799,6 +799,18 @@ struct JS_PUBLIC_API JSContext : public JS::RootingContext,
     return JS::IsCatchableExceptionStatus(status);
   }
 
+  void setInterrupting() {
+    MOZ_ASSERT(status == JS::ExceptionStatus::None);
+    status = JS::ExceptionStatus::Interrupt;
+  }
+  void clearInterrupt() {
+    // NOTE: Calling `setInterrupting` is still optional, but certainly there
+    //       should not be any catchable exception pending.
+    MOZ_ASSERT(status == JS::ExceptionStatus::None ||
+               status == JS::ExceptionStatus::Interrupt);
+    status = JS::ExceptionStatus::None;
+  }
+
   [[nodiscard]] bool getPendingException(JS::MutableHandleValue rval);
 
   js::SavedFrame* getPendingExceptionStack();

js/src/vm/Runtime.cpp

@@ -482,6 +482,8 @@ static bool HandleInterrupt(JSContext* cx, bool invokeCallback) {
     chars = u"(stack not available)";
   }
   WarnNumberUC(cx, JSMSG_TERMINATED, chars);
+
+  cx->setInterrupting();
   return false;
 }
 

js/xpconnect/src/XPCShellImpl.cpp

@@ -423,6 +423,7 @@ static bool Quit(JSContext* cx, unsigned argc, Value* vp) {
 
   gQuitting = true;
   //    exit(0);
+  JS_SetPendingInterrupt(cx);
   return false;
 }