Bug 1791292 - Expose nsresult for file-not-found error. r=jonco

Differential Revision: https://phabricator.services.mozilla.com/D157700

js/xpconnect/loader/ComponentModuleLoader.cpp

@@ -9,6 +9,9 @@
 #include "nsISupportsImpl.h"
 
 #include "js/loader/ModuleLoadRequest.h"
+#include "js/RootingAPI.h"          // JS::Rooted
+#include "js/PropertyAndElement.h"  // JS_SetProperty
+#include "js/Value.h"               // JS::Value, JS::NumberValue
 #include "mozJSModuleLoader.h"
 
 using namespace JS::loader;
@@ -125,6 +128,17 @@ nsresult ComponentModuleLoader::StartFetch(ModuleLoadRequest* aRequest) {
       return NS_ERROR_OUT_OF_MEMORY;
     }
 
+    if (mLoadException.isObject()) {
+      // Expose `nsresult`.
+      JS::Rooted<JS::Value> resultVal(cx, JS::NumberValue(uint32_t(rv)));
+      JS::Rooted<JSObject*> exceptionObj(cx, &mLoadException.toObject());
+      if (!JS_SetProperty(cx, exceptionObj, "result", resultVal)) {
+        // Ignore the error and keep reporting the exception without the result
+        // property.
+        JS_ClearPendingException(cx);
+      }
+    }
+
     return rv;
   }
 

js/xpconnect/tests/unit/test_import_es6_modules.js

@@ -26,6 +26,7 @@ add_task(async function() {
     stack: "testFailure",
     lineNumber: "*",
     columnNumber: "*",
+    result: Cr.NS_ERROR_FILE_NOT_FOUND,
   });
 
   // Test load failure in import.
@@ -36,6 +37,7 @@ add_task(async function() {
     stack: "testFailure",
     lineNumber: "*",
     columnNumber: "*",
+    result: Cr.NS_ERROR_FILE_NOT_FOUND,
   });
 
   // Test parse error.
@@ -172,4 +174,7 @@ function checkException(exception, expected, importLine, importColumn) {
     }
     Assert.equal(exception.columnNumber, expectedColumn, "columnNumber");
   }
+  if ("result" in expected) {
+    Assert.equal(exception.result, expected.result, "result");
+  }
 }