assert: use stricter stack frame detection in .ifError()

This makes sure arbitrary stack traces are not handled as stack
frames.

Signed-off-by: Ruben Bridgewater <ruben@bridgewater.de>

lib/assert.js

@@ -966,21 +966,23 @@ assert.ifError = function ifError(err) {
       // This will remove any duplicated frames from the error frames taken
       // from within `ifError` and add the original error frames to the newly
       // created ones.
-      const tmp2 = StringPrototypeSplit(origStack, '\n');
-      ArrayPrototypeShift(tmp2);
-      // Filter all frames existing in err.stack.
-      let tmp1 = StringPrototypeSplit(newErr.stack, '\n');
-      for (const errFrame of tmp2) {
-        // Find the first occurrence of the frame.
-        const pos = ArrayPrototypeIndexOf(tmp1, errFrame);
-        if (pos !== -1) {
-          // Only keep new frames.
-          tmp1 = ArrayPrototypeSlice(tmp1, 0, pos);
-          break;
+      const origStackStart = origStack.indexOf('\n    at');
+      if (origStackStart !== -1) {
+        const originalFrames = StringPrototypeSplit(origStack.slice(origStackStart + 1), '\n');
+        // Filter all frames existing in err.stack.
+        let newFrames = StringPrototypeSplit(newErr.stack, '\n');
+        for (const errFrame of originalFrames) {
+          // Find the first occurrence of the frame.
+          const pos = ArrayPrototypeIndexOf(newFrames, errFrame);
+          if (pos !== -1) {
+            // Only keep new frames.
+            newFrames = ArrayPrototypeSlice(newFrames, 0, pos);
+            break;
+          }
         }
+        newErr.stack =
+          `${ArrayPrototypeJoin(newFrames, '\n')}\n${ArrayPrototypeJoin(originalFrames, '\n')}`;
       }
-      newErr.stack =
-        `${ArrayPrototypeJoin(tmp1, '\n')}\n${ArrayPrototypeJoin(tmp2, '\n')}`;
     }
 
     throw newErr;

test/parallel/test-assert-if-error.js

@@ -39,6 +39,18 @@ const stack = err.stack;
   })();
 })();
 
+assert.throws(
+  () => {
+    const error = new Error();
+    error.stack = 'Error: containing weird stack\nYes!\nI am part of a stack.';
+    assert.ifError(error);
+  },
+  (error) => {
+    assert(!error.stack.includes('Yes!'));
+    return true;
+  }
+);
+
 assert.throws(
   () => assert.ifError(new TypeError()),
   {