FR: Filter functions to emulate, write out rules coverage to file

[SamyPesse]

Right now there is no way to do only start the emulator with a subset of functions enabled instead of all. It requires a custom build or filter the exports ourself.

It'd be great if the firebase emulators:exec and firebase emulators:start would accept an argument like --functions a,b or maybe the same syntax as firebase deploy: --only functions:a,functions:b (this is what I was expecting at first)

[samtstern]

@SamyPesse this is a reasonable feature request and should be feasible to implement. Can you explain the reason that you don't want to emulate all functions though? Curious if there's an underyling emulator improvement we could make.

[SamyPesse]

I'm basically running a script generate-tests-data to prepare the dataset for unit testing:

export CF_IS_PREPARING_DATASET="true"

firebase emulators:exec --only firestore,functions \
    "yarn node write-to-emulator.ts && \
    sleep 60 && \
    curl http://localhost:8080/emulator/v1/projects/$PROJECT_ID:ruleCoverage.html > tests/coverages/firestore.html && \
    firebase emulators:export ./dump/tests --force"

To explain this code:

• We start the functions emulator because some documents are "computed" in cloud functions
• We use CF_IS_PREPARING_DATASET to have different exports and not run all functions, because only a few are used to compute those data, and most other functions depend on external services
• We use sleep 60 to wait for the end of the CF executions 🙃
• We use the curl to access the coverage after executing the command

The improvements I'd like from Firebase are:

• Specify functions to run in firebase emulators:exec to avoid the use of an env CF_IS_PREPARING_DATASET to return a different set of functions
• A command firebase emulators:functions:wait to wait for all cloud functions executions to be finished (similar to https://github.com/firebase/firebase-tools/issues/1813)

[samtstern]

@SamyPesse I just sent a PR to fix #1813 which will be included in the next release. We'll now wait up to 60s for any functions to finish when the emulators are stopped.

[SamyPesse]

Thanks @samtstern, but we'll probably have to keep using the bash script with the sleep 60 because we want to run curl http://localhost:8080/emulator/v1/projects/$PROJECT_ID:ruleCoverage.html > tests/coverages/firestore.html to download the rules coverage before the emulator is killed

[samtstern]

@SamyPesse makes sense I actually end up in this situation a lot. Would it be useful for you if the emulator always wrote the rules coverage report to a file on exiting? Or do you prefer to have more control over when/where that happens?

[SamyPesse]

@samtstern yes it'll fix it 👍