Avoid reporting errors twice

Author: robertbrignull

extensions/ql-vscode/src/view/common/errors.ts

@@ -1,24 +1,47 @@
 import { getErrorMessage, getErrorStack } from "../../pure/helpers-pure";
 import { vscode } from "../vscode-api";
 
+// Keep track of previous errors that have happened.
+// The listeners for uncaught errors and rejections can get triggered
+// twice for each error. This is believed to be an effect caused
+// by React's error boundaries. Adding an error boundary stops
+// this duplicate reporting for errors that happen during component
+// rendering, but unfortunately errors from event handlers and
+// timeouts are still duplicated and there does not appear to be
+// a way around this.
+const previousErrors: Set<Error> = new Set();
+
+function shouldReportError(error: Error): boolean {
+  const seenBefore = previousErrors.has(error);
+  previousErrors.add(error);
+  setTimeout(() => {
+    previousErrors.delete(error);
+  }, 1000);
+  return !seenBefore;
+}
+
 const unhandledErrorListener = (event: ErrorEvent) => {
-  vscode.postMessage({
-    t: "unhandledError",
-    error: {
-      message: getErrorMessage(event.error),
-      stack: getErrorStack(event.error),
-    },
-  });
+  if (shouldReportError(event.error)) {
+    vscode.postMessage({
+      t: "unhandledError",
+      error: {
+        message: getErrorMessage(event.error),
+        stack: getErrorStack(event.error),
+      },
+    });
+  }
 };
 
 const unhandledRejectionListener = (event: PromiseRejectionEvent) => {
-  vscode.postMessage({
-    t: "unhandledError",
-    error: {
-      message: getErrorMessage(event.reason),
-      stack: getErrorStack(event.reason),
-    },
-  });
+  if (shouldReportError(event.reason)) {
+    vscode.postMessage({
+      t: "unhandledError",
+      error: {
+        message: getErrorMessage(event.reason),
+        stack: getErrorStack(event.reason),
+      },
+    });
+  }
 };
 
 /**