Bug 1637883 - Bail on eager eval for same-compartment windows. r=nchevobbe

Differential Revision: https://phabricator.services.mozilla.com/D81382

devtools/server/actors/webconsole/eval-with-debugger.js

@@ -217,6 +217,13 @@ function getEvalResult(
   noSideEffectDebugger
 ) {
   if (noSideEffectDebugger) {
+    // Bug 1637883 demonstrated an issue where dbgWindow was somehow in the
+    // same compartment as the Debugger, meaning it could not be debugged
+    // and thus cannot handle eager evaluation. In that case we skip execution.
+    if (!noSideEffectDebugger.hasDebuggee(dbgWindow.unsafeDereference())) {
+      return null;
+    }
+
     // When a sideeffect-free debugger has been created, we need to eval
     // in the context of that debugger in order for the side-effect tracking
     // to apply.