Task Execution Dependencies for failed task

[JeremyRand]

Description

It would be useful to make a task depend on another task failing (as opposed to the status quo, where a task dependency can only depend on a task succeeding). Or, alternatively, make a task depend on the build as a whole failing.

Context

I'd like to have a dedicated task that pings my IRC channel when a build fails. Relying on a GitHub Action for this purpose is not an option, because GitHub Actions demand substantially more permissions than are needed for this, and are therefore a security risk for me.

[fkorotkov]

I think it can be a part of https://github.com/cirruslabs/cirrus-cli/issues/143 which will allow to have basically a "lambda" on a build status change. This Starlark "lambda" will be able to send an HTTP request instantaneously or yeild a new set of tasks to schedule.

Right now people workaround it via webhooks and their own apps.