Functions emulator triggers on delete of document that does not exist

[wooliet]

[REQUIRED] Environment info

firebase-tools: 9.1.0

Platform: macOS

[REQUIRED] Test case

A. Cloud function set to trigger on document "write" events:

exports.onDocWrite = functions.firestore.document(
  '/test-collection/{id}'
).onWrite(change => {
  const orig = change.before.data();
  console.log(orig);
  return true;
});

B. Code that deletes a document to trigger onDocWrite

async function main () {
  const ref = admin.firestore().doc(
    '/test-collection/QdfGrVXTYqPqIOxuXpbp'
  );
  await ref.delete();
  process.exit(0);
}

[REQUIRED] Steps to reproduce

1. Create the onDocWrite firestore cloud function and deploy to production environment
2. Manually add a new document to test-collection
3. Run code to delete the document and observe logged output
4. Run code to delete the document again: no logged output
5. Repeat the above steps against the emulated environment

[REQUIRED] Expected behavior

Emulated environment should produce no logged output when deleting a document that does not exist.

[REQUIRED] Actual behavior

Cloud function in emulated environment is triggered on delete of the document that does not exist. It logs "undefined" for the document's before.data().

i  functions: Beginning execution of "onDocWrite"
i  functions: Finished "onDocWrite" in ~1s
>  undefined

[samtstern]

@wooliet good catch and thank you for the detailed issue! I can confirm this:

Functions code:

const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp();

exports.onDocWrite = functions.firestore.document('/test-collection/{id}').onWrite(change => {
  console.log("before:", change.before.data());
  console.log("after:", change.after.data());
  return true;
});

exports.runTest = functions.https.onRequest(async (request, response) => {
  const db = admin.firestore();
  const ref = db.collection('test-collection').doc();

  console.log("Setting...");
  await ref.set({
    hello: 'world'
  });
  console.log("Get 1: ", (await ref.get()).data());

  console.log("Deleting once...");
  await ref.delete();
  console.log("Get 2: ", (await ref.get()).data());

  console.log("Deleting twice...");
  await ref.delete();

  response.json({ status: 'ok' });
});

Logs:

i  functions: Beginning execution of "runTest"
>  Setting...
>  Get 1:  { hello: 'world' }
>  Deleting once...
>  Get 2:  undefined
>  Deleting twice...
i  functions: Finished "runTest" in ~1s
i  functions: Beginning execution of "onDocWrite"
>  before: undefined
>  after: { hello: 'world' }
i  functions: Finished "onDocWrite" in ~1s
i  functions: Beginning execution of "onDocWrite"
i  functions: Finished "onDocWrite" in ~1s
>  before: { hello: 'world' }
>  after: undefined
i  functions: Beginning execution of "onDocWrite"
i  functions: Finished "onDocWrite" in ~1s
>  before: undefined
>  after: undefined

[samtstern]

Assigning to @yuchenshi who is on call for emulator issues this week.

[yuchenshi]

This seems like a bug in Firestore emulator. I've filed b/176544363 internally to track this.